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  • Sustainable intensification in agricultural systems
    reserved For Permissions please email journals permissions oup com Related articles ContentSnapshots Content Snapshots Ann Bot 2014 114 8 i iii doi 10 1093 aob mcu241 Extract Full Text HTML Full Text PDF Previous Next Article Table of Contents This Article Ann Bot 2014 114 8 1571 1596 doi 10 1093 aob mcu205 First published online October 28 2014 Abstract Free Free Figures Free Full Text HTML Free Full Text PDF Free All Versions of this Article mcu205v1 114 8 1571 most recent Classifications Invited Review Services Article metrics Alert me when cited Alert me if corrected Alert me if commented Find similar articles Similar articles in Web of Science Similar articles in PubMed Add to my archive Download citation Request Permissions Responses Submit a response No responses published Citing Articles Load citing article information Citing articles via CrossRef Citing articles via Scopus Citing articles via Web of Science Citing articles via Google Scholar Google Scholar Articles by Pretty J Articles by Bharucha Z P Search for related content PubMed PubMed citation Articles by Pretty J Articles by Bharucha Z P Agricola Articles by Pretty J Articles by Bharucha Z P Related Content Related articles in this journal Ecology Load related web page information Share Email this article CiteULike Delicious Facebook Google Mendeley Twitter What s this Search this journal Advanced Current Issue February 2016 117 2 Alert me to new issues The Journal About this journal Annals of Botany Collections AoB article attracts media coverage We are mobile find out more Journals Career Network Published on behalf of The Annals of Botany Company Impact factor 3 654 5 Yr impact factor 4 338 Eigenfactor 0 02603 Rank 10 200 SCImago Score 1 461 Rank 124 1873 Chief Editor Professor J S Pat Heslop Harrison View full editorial board International

    Original URL path: https://aob.oxfordjournals.org/content/114/8/1571.figures-only?sid=b5a6bc25-5f3c-4c5f-a5e2-76b73d864083 (2016-02-18)
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  • Ecophysiology of gelatinous Nostoc colonies: unprecedented slow growth and survival in resource-poor and harsh environments
    limited by diffusion at low concentrations for all species although they exhibit efficient HCO 3 uptake accumulation of respiratory DIC within the colonies and very low CO 2 compensation points Long light paths and light attenuation by structural substances in large Nostoc colonies cause lower quantum efficiency and assimilation number and higher light compensation points than in unicells and other aquatic macrophytes Extremely low growth and mortality rates of N zetterstedtii reflect stress selected adaptation to nutrient and DIC poor temperate lakes while N pruniforme exhibits a mixed ruderal and stress selected strategy with slow growth and year long survival prevailing in sub Arctic lakes and faster growth and shorter longevity in temperate lakes Nostoc commune and its close relative N flagelliforme have a mixed stress disturbance strategy not found among higher plants with stress selection to limiting water and nutrients and disturbance selection in quiescent dry or frozen stages Despite profound ecological differences between species active growth of temperate specimens is mostly restricted to the same temperature range 0 35 C maximum at 25 C Future studies should aim to unravel the processes behind the extreme persistence and low metabolism of Nostoc species under ambient resource supply on sediment and soil surfaces Key words Gelatinous colonies cyanobacteria Nostoc commune Nostoc flagelliforme Nostoc pruniforme Nostoc zetterstedtii carbon use carbon concentrating mechanisms photosynthesis light use growth long lived survival desiccation tolerance nutrient poor The Author 2014 Published by Oxford University Press on behalf of the Annals of Botany Company All rights reserved For Permissions please email journals permissions oup com Related articles ContentSnapshots Content Snapshots Ann Bot 2014 114 1 i iii doi 10 1093 aob mcu136 Extract Full Text HTML Full Text PDF Previous Next Article Table of Contents This Article Ann Bot 2014 114 1 17 33 doi 10 1093 aob mcu085 Abstract Free Free Figures Free Full Text HTML Free Full Text PDF Free Classifications Invited Review Services Article metrics Alert me when cited Alert me if corrected Alert me if commented Find similar articles Similar articles in Web of Science Similar articles in PubMed Add to my archive Download citation Request Permissions Responses Submit a response No responses published Citing Articles Load citing article information Citing articles via CrossRef Citing articles via Scopus Citing articles via Web of Science Citing articles via Google Scholar Google Scholar Articles by Sand Jensen K Search for related content PubMed PubMed citation Articles by Sand Jensen K Agricola Articles by Sand Jensen K Related Content Related articles in this journal Ecology Load related web page information Share Email this article CiteULike Delicious Facebook Google Mendeley Twitter What s this Search this journal Advanced Current Issue February 2016 117 2 Alert me to new issues The Journal About this journal Annals of Botany Collections AoB article attracts media coverage We are mobile find out more Journals Career Network Published on behalf of The Annals of Botany Company Impact factor 3 654 5 Yr impact factor 4 338 Eigenfactor 0 02603 Rank 10

    Original URL path: https://aob.oxfordjournals.org/content/114/1/17.abstract?sid=b5a6bc25-5f3c-4c5f-a5e2-76b73d864083 (2016-02-18)
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  • Ecophysiology of gelatinous Nostoc colonies: unprecedented slow growth and survival in resource-poor and harsh environments
    b though higher concentrations can occur at the sediment surface For a DIP gradient of 0 3 m m across a 1 mm thick DBL the estimated influx was 0 22 nmol P cm 2 h 1 for small colonies radius 1 mm and 0 12 nmol P cm 2 h 1 for large colonies radius 10 mm These fluxes should permit a turnover time of the P pool within 6 d for small and 72 d for large colonies of N zetterstedtii supporting the hypothesis that growth is more likely to be constrained by the supply rate of DIC across gradients of 0 1 m m HCO 3 These calculations agreed with the observation that growth was unaffected by P richness in the sediments of soft water Lake Värsjö Sand Jensen and Møller 2011 DIC supply is also important in dense epilithic communities growing on inert substrata and covered by relatively thick boundary layers Sand Jensen 1983 Thus short epilithic algal communities in marine waters have DBL thicknesses similar to those applied for Nostoc colonies and they appear to be constrained by the DIC flux to photosynthesis despite high HCO 3 concentration 2 m m in seawater Larkum et al 2003 showed that DBLs of epilithic algal communities covering dead coral surfaces were 0 18 0 59 mm thick under moderate flow 8 cm s 1 and 2 mm under quasi stagnant conditions and they generated high resistance to DIC influx limiting primary production Independent experiments with epilithic algal communities in other coral reef environments appeared to support the conclusion that DIC is a main limiting factor as elevated nutrient levels had no effect on primary production and growth Larkum and Koop 1997 Miller et al 1999 while large macroalgae in such nutrient poor waters were stimulated by nutrient amendment Lapointe et al 1987 Resource supply solely by diffusion The flux to Nostoc colonies may be controlled entirely by diffusion in a stagnant water layer overlying the sediment A stagnant surface layer may exist almost permanently in deep water with restricted turbulence and periodically in shallow water during calm weather The colonies could be buried in a viscous boundary layer a few centimetres thick overlying the sediment Boudreau and Jørgensen 2001 When the surrounding water is virtually stagnant and the solute concentration is reduced to zero at the colony surface the flux per unit surface area is inversely scaled to colony radius emphasizing the immense advantage of being small eqn 3 in Table 3 The calculated flux is 720 nmol C cm 2 h 1 for small colonies radius 1 mm in water containing 2 m m HCO 3 or half the flux that occurs when DBL is 1 mm thick eqn 1 For large colonies radius 10 mm however the flux in stagnant water is only 72 nmol C cm 2 h 1 or 11 fold lower than in stirred water with a DBL of 1 mm The potential biomass turnover time for large colonies as described above would then be 120 d for N pruniforme under stagnant conditions in hard water lakes and 32 350 d 89 years for N zetterstedtii in soft water lakes Both values are very high stressing that the water overlying the sediment is either not entirely stagnant or is enriched with DIC CO 2 and HCO 3 from sediment decomposition Maberly s 1985 measurements 10 cm above the sediments in a shallow bay covered by the moss Fontinalis antipyretica showed elevated CO 2 concentrations relative to surface waters between 0 05 and 0 26 m m on 14 different dates Concentrations are higher directly on the sediment surface and a near bed CO 2 concentration of for example 0 3 m m CO 2 could permit a 6 fold higher influx of CO 2 than a HCO 3 gradient of 0 1 m m because the diffusion coefficient of CO 2 is approximately twice that of HCO 3 Denny 1993 The resulting turnover time could then be 6 3 years for large colonies of N zetterstedtii if we assume that the granulated surface doubles the influx and 3 2 years if the inward flux continues in both light and darkness Thus we cannot exclude that large colonies of N zetterstedtii could survive in an entirely diffusive environment provided available concentrations of CO 2 and HCO 3 were markedly higher than 0 1 m m Small colonies a few millimetres in diameter can perform well by diffusive fluxes alone and are likely to be fully embedded in a diffusive boundary above the sediment surface Resource supply by diffusion relative to colony volume The diffusive flux through stagnant water to a smooth spherical colony follows the well known formula often used for bacteria eqn 4 in Table 3 Fenchel et al 1998 because the colonies are usually so small relative to the thickness of DBL that the supply rate is entirely determined by diffusion When metabolic activity and the demand for external resources are evenly distributed throughout the colony volume the flux relative to unit volume F v will be inversely scaled to the second power of radius emphasizing the likelihood of extreme limitation as the organisms grow in size eqn 5 in Table 3 The solutions to cope with this rapidly increasing risk of resource limitation with larger size would be either to reduce volume specific requirements for metabolism in the case of N zetterstedtii or develop a hollow sphere where all activity is restricted to an outer shell of thickness L s and volume 4 3π r 3 r L s 3 4π r 0 5 L s 2 L s When r is large relative to L s volume is close to 4π r 2 L s and the flux relative to volume of the outer shell F vs declines linearly with colony radius eqn 6 in Table 3 Thus a 10 fold increase in colony radius will reduce the flux relative to the surface area and volume of a hollow spherical colony by the same order of magnitude while the flux relative to the volume of a homogeneous solid spherical colony declines 100 fold emphasizing that if large colonies are indeed solid then their central parts must be composed of recalcitrant matrix material and either have no cells or cells of low metabolism Because N zetterstedtii colonies with a diameter of 10 20 mm absorb 96 of incident irradiance from the surface to the centre Sand Jensen et al 2009 b there is no scope for photosynthesis of Nostoc trichomes in the centre but there is organic matter present here that could potentially be used by heterotrophic bacteria The colony matrix is persistent and protected by bactericides Sand Jensen et al 2009 a however implying that there are no or very few active heterotrophic bacteria living within N zetterstedtii colonies The year long persistence and low respiration rates of the colonies in complete darkness support this implication see below Efflux of solutes While the large size of gelatinous Nostoc colonies constrains the influx of external resources it will also limit the efflux of valuable dissolved products derived from metabolism within the colonies The possible implications of variations in this efflux have been overlooked so far When the diffusive loss of respiratory CO 2 and inorganic nutrients e g phosphate from the colony is constrained they can better be retained and recycled within the colony see section Size effects diffusive supply and loss of solutes Organic compounds that are produced and to a great extent released from the trichomes to form the extensive colony matrix can also be lost to the surrounding water and this loss can presumably be reduced in large colonies Perhaps more importantly antibiotics and toxins produced by Nostoc to reduce the risks of being attacked by harmful bacteria viruses mixotrophic algae and animals can be retained within the colony and here reach highly effective concentrations for a limited rate of production Thus with increasing colony size a constant production rate of the protective substance per colony volume will lead to increasing internal concentrations or a constant internal concentration can be attained despite a declining production rate of the protective substance The formal analysis shows that a solute produced by a massive spherical organism at a uniform specific rate per unit volume P v and lost by diffusion to stagnant surrounding water with a zero background concentration will have an effective concentration right at the surface of the colony that increases by the second power of the radius eqn 7 in Table 3 If the concentration is kept constant the production rate can decline by the second power of the radius The mathematical formulas have been derived from Denny 1993 who treated an analogue biological example Photosynthetic production is constant relative to the surface area of N pruniforme and N zetterstedtii Raun et al 2009 Sand Jensen et al 2009 b in accordance with the fact that photosynthesis is confined to a surface shell of thickness L sh and an approximate volume of 4π r 2 L sh Because protective substances derive from photosynthetic products they could have the same scaling properties Thus inserting shell volume instead of total colony volume in eqn 7 predicts that the concentration on the colony surface would increase in proportion to colony radius eqn 8 in Table 3 Alternatively the concentration would remain constant if the production rate of protective substances declined in proportion to increasing colony radius Therefore the incorporation rate of inorganic carbon into new cells colony matrix and extracellular products should all be determined as a function of colony size This would permit direct determination of turnover rates of cells and colony matrix and evaluation of the relative cost of producing and releasing extracellular products Despite extensive and elaborate work on the biochemistry of Nostoc colonies this analysis has not been performed as yet Previous Section Next Section FUNCTIONAL CONSEQUENCES OF THE USE OF LIGHT AND INORGANIC CARBON Nostoc concentrates and circulates inorganic carbon efficiently within the large colonies while the use of light suffers from extensive self shading and absorption by non photosynthetic elements Use of light The large size long internal light paths and high densities of trichomes within Nostoc colonies imply that light absorptance and internal self shading are high Mean light absorptance ranged from 55 in N commune to 96 in N zetterstedtii Table 4 Moreover because the cells experience high O 2 and low CO 2 concentrations within the colonies during photosynthesis maximum photosynthesis relative to cell chlorophyll i e the assimilation number maximum quantum efficiency of photosynthesis and the ratio of photosynthesis to respiration should be much lower than among free living unicells To the extent that photons are absorbed by non photosynthetic pigments and other coloured substances inside the colonies maximum quantum efficiency will decline further View this table In this window In a new window Table 4 Photosynthesis light variables of three Nostoc species at 15 C Quantum efficiency was indeed low for N commune average 19 1 mmol O 2 mol absorbed photon 1 and N zetterstedtii 11 2 39 9 in three series Table 4 A similarly low efficiency 27 mmol O 2 mol photon 1 was calculated for the thick walled balloon like green macroalga Codium bursa Geertz Hansen et al 1994 and microbial mats with extensive absorption 40 80 by structural components Al Najjar et al 2012 In contrast quantum efficiencies are much higher for free living microalgae 70 120 mmol O 2 mol photon 1 macroalgae and submerged plants 37 79 mmol O 2 mol photon 1 Frost Christensen and Sand Jensen 1992 Nostoc zetterstedtii had particularly low light saturated photosynthesis relative to chlorophyll average 0 5 0 7 mg O 2 mg 1 chlorophyll a h 1 and values were also low for N commune average 2 4 and N pruniforme average 2 1 Likewise photosynthesis relative to dark respiration NP R was low for N zetterstedtii 2 0 5 8 and N commune average 2 5 but not for N pruniforme average 10 Again free living unicells have higher rates of photosynthesis relative to chlorophyll typically between 2 and 20 Harris 1978 and NP R ratios from 5 to 20 Harris 1978 Geider and Osborne 1992 High self shading within Nostoc colonies is an important constraint because photosynthesis at high irradiance increased 4 fold and NP R increased 3 fold when self shading was reduced by cutting colonies of N zetterstedtii into 1 2 mm pieces Sand Jensen et al 2009 b Light attenuation by coloured substances structural substances and dead or senescent cells within the colonies competes with photosynthetic pigments for photons and thereby lowers quantum efficiency and increases the light compensation point where photosynthesis outweighs respiration compared with free living unicells Krause Jensen and Sand Jensen 1998 Al Najjar et al 2012 Thus light compensation points of N zetterstedtii and N commune 9 5 19 3 μmol photon m 2 s 1 exceeded those of most unicells typically 0 8 9 μmol m 2 s 1 Langdon 1988 and thin thalli and leaves of macroalgae and submerged plants typically 2 12 μmol m 2 s 1 Sand Jensen and Madsen 1991 This comparison supports the hypothesis that inefficient light use in Nostoc colonies combined with higher respiratory costs of producing and maintaining the colony should lead to higher minimum light requirements for survival than for unicells characeans and plants with thin photosynthetic tissues Observations of lower light availability at the maximum depth limits of characeans filamentous algae and mosses 3 1 7 8 of surface light than of N pruniforme and N zetterstedtii 9 4 12 5 of surface light in two Danish lakes support this hypothesis Table 7 in Sand Jensen et al 2009 b Use of inorganic carbon The diffusive supply of DIC from outside is constrained by the large size low SA V ratio and high density of filaments in the 1 3 mm thick outer shells of gelatinous Nostoc colonies without direct contact with the surrounding medium The effective diffusion path involves both the diffusive boundary layer surrounding the colony and the path through the gel to the sites of fixation in the Nostoc filaments but the internal resistance has not been accounted for While increasing the resistance to influx of gas and solutes the gel will also slow effluxes and contribute to the retention of night time respiratory CO 2 and facilitate accumulation of internal DIC pools To ameliorate carbon limitation of photosynthesis and prevent excessive photorespiration Nostoc colonies like other cyanobacteria Badger and Price 1992 2003 must attain reasonably high quotients of CO 2 to O 2 at the site of Rubisco activity within the cells To achieve this Nostoc colonies must be able to extract high proportions of the DIC pool in the water and have low compensation points of CO 2 and HCO 3 Sültemeyer et al 1998 The ability to accumulate DIC pools within the colony above immediate needs for photosynthesis and to retain respiratory CO 2 from night time respiration for later use during daytime photosynthesis could assist the carbon supply even further Such efficient extraction and accumulation of carbon are known for free living cyanobacteria Kaplan et al 1980 Sültemeyer et al 1998 and phototrophs in lichen photosynthesis Green et al 1994 and the potential may also exist for Nostoc trichomes buried within the colony gel We found a high mean extraction capacity of between 74 and 82 of the initial DIC pool in the water 0 3 1 1 m m during 20 h of photosynthesis in closed bottles with N commune and N zetterstedtii where DIC was gradually depleted and pH and O 2 increased over time Table 5 The mean extraction capacity was lower 58 but probably not fully expressed in experiments with N pruniforme though it still reflected very active DIC uptake Efficient DIC use is also known for N flagelliforme and edible Nostoc Ge Xian Me Gao and Zou 2001 Qiu et al 2004 Ye et al 2012 Efficient active use of external DIC by N commune and N zetterstedtii was also reflected in the high final pH in the surrounding water 10 60 11 11 and the low final concentrations of HCO 3 6 75 μ m and CO 2 0 3 7 n m as measures of HCO 3 and CO 2 compensation points Table 6 Concentrations of HCO 3 and CO 2 at the sites of Rubisco within the cells must be markedly higher and molar quotients of O 2 to HCO 3 CO 2 lower than in the surrounding water 8 60 to ensure net carbon fixation and reduce photorespiration Kaplan et al 1980 Price et al 2008 View this table In this window In a new window Table 5 Extraction capacity of the initial DIC pool of three Nostoc species during photosynthesis for 20 h in closed bottles View this table In this window In a new window Table 6 Final pH final DIC HCO 3 and CO 2 and final O 2 HCO 3 ratio of the four Nostoc species after 20 h of photosynthesis in closed bottles Ranges are shown from several experimental series with many replicates The ability of all three Nostoc species to accumulate DIC to much higher concentrations within the colony than in the external water is supported by the relatively high rates of O 2 release by photosynthesis for 20 h in water of low DIC 0 1 m m 0 1 μmol cm 3 without any appreciable uptake of external DIC Assuming that O 2 is produced and inorganic C consumed from the colony itself during extended photosynthesis with a molar quotient of 1 0 we determined that a DIC pool of 16 3 24 5 μmol g 1 FM was available for photosynthesis in colonies of N zetterstedtii and about half this pool size 5 8 10 2 μmol g 1 FM was available in N commune and N pruniforme Table 7 Direct measurements of the internal DIC pool in N zetterstedtii yielded 19 0 24 7 μmol g 1 FM for colonies incubated in water containing 0 15 m m DIC and these measurements fully corresponded with estimates derived from the O 2 DIC balance Sand Jensen et al 2009 b Measured DIC concentrations were 150 fold higher within the colonies average of cells and matrix than in the external water and I expect that DIC concentrations would be even higher within the cells resulting in a higher accumulation quotient than 150 between cells and water Accumulation quotients of 500 1000 are known for free living cyanobacteria Kaplan et al 1980 Badger and Price 2003 View this table In this window In a new window Table 7 DIC consumed from the colony volume of three Nostoc species during extended light periods 20 h When I accounted for exchange of DIC during photosynthesis and respiration with both the colony matrix and the external water I found mean molar exchange quotients of O 2 relative to DIC in the light 1 19 and in the dark 0 96 close to 1 0 in experiments with N zetterstedtii Fig 3 These direct measurements confirmed that a high proportion of DIC for photosynthesis in the light was consumed from a DIC pool in the colony while in the dark a high proportion of respiratory DIC accumulated within the colony Fig 3 The measured internal DIC pools in N zetterstedtii could support maximum photosynthesis for 11 and 23 h in 10 and 20 mm diameter colonies respectively without uptake of external DIC When N commune was incubated for 20 h in relatively DIC rich water containing initially 1 1 m m it accumulated 16 7 18 7 μmol DIC g 1 FM of colony in excess of the immediate requirements for photosynthesis while it consumed 9 10 2 μmol DIC g 1 FM from the colony to support photosynthesis when the initial DIC concentration in the water was only 0 2 m m K Sand Jensen unpubl data Photosynthetic ATP production provides ample energy for active transport of HCO 3 and at least N commune can consume DIC for photosynthesis and at the same time accumulate DIC within the colony in the light when sufficient external DIC is available Thus the species does not solely rely on accumulation of respiratory DIC in the dark but can also take up external HCO 3 for use in the following light period The ability of Nostoc colonies to build up substantial internal DIC pools had been overlooked in the past This ability means that photosynthesis is less dependent on the immediate external DIC supply Nonetheless all three species were limited by the external DIC supply as photosynthetic rates at 0 1 m m DIC externally were 20 of the maximum rate for N commune 11 for small 13 for medium sized and 25 for large colonies of N pruniforme and 60 for N zetterstedtii Figs 4 and 5 As the internal DIC pool in N zetterstedtii colonies is gradually exhausted during 18 h of light incubation in closed bottles realized mean rates of O 2 production are 1 8 fold lower in water initially containing 0 29 m m compared with water initially containing 0 99 m m DIC Fig 3 In N pruniforme which has higher rates of photosynthesis and DIC requirements per surface area than N zetterstedtii and apparently 2 fold lower internal DIC pools the dependency of photosynthesis on external DIC was stronger showing half saturation constants of 0 78 m m for small colonies 0 1 g FM and 1 24 m m for larger colonies 2 5 g FM in 2 h experiments under well stirred conditions Fig 4 Large colonies have higher rates of photosynthesis 164 nmol O 2 cm 2 h 1 at near zero external DIC than small colonies 55 nmol O 2 cm 2 h 1 probably because of a larger internal DIC pool being scaled to colony volume relative to photosynthetic activity being scaled to colony surface area The more favourable SA V ratio in small colonies causes photosynthesis to increase more steeply with increasing external DIC α CO 2 319 nmol O 2 cm 2 h 1 for a 1 mmol L 1 increase in external DIC than in large colonies α CO 2 197 nmol O 2 cm 2 h 1 mmol DIC L 1 1 Fig 4 View larger version In this window In a new window Download as PowerPoint Slide Fig 4 Mean net photosynthesis s d of four replicates of small 0 18 g FM medium 0 84 g FM and large 2 71 g FM spherical colonies of N pruniforme as a function of external DIC concentration 95 HCO 3 The apparent half saturation constant for small medium and large colonies was 0 78 0 78 and 1 24 m m HCO 3 the initial linear slope of net photosynthesis at low limiting DIC concentration was 319 305 and 197 nmol O 2 cm 2 h 1 1 mmol DIC L 1 1 and photosynthesis extrapolated to zero DIC was 55 72 and 164 nmol O 2 cm 2 h 1 From Raun 2006 View larger version In this window In a new window Download as PowerPoint Slide Fig 5 Mean DIC uptake during photosynthesis in high light as a function of mean DIC concentration in the water for N commune N pruniforme and N zetterstedtii Sources N commune K Sand Jensen unpubl data N pruniforme Raun et al 2009 N zetterstedtii Sand Jensen et al 2009 b The terrestrial and semi terrestrial N commune and N flagelliforme can use CO 2 and HCO 3 under water and CO 2 alone in air Under water N commune experiences limitation of photosynthesis at low DIC as rates rise to at least 1 m m The diffusion coefficient of CO 2 in air is 2 10 4 times higher than that of HCO 3 in water and for the same DBL thickness and with complete DIC depletion at the colony surface the CO 2 gradient is 30 50 times lower in air external CO 2 0 02 m m than in water containing 0 6 1 0 m m HCO 3 Thus the potential flux would be substantially higher 500 to 700 fold in air than in water through a diffusive boundary layer of the same thickness overlying the colony surface but this is followed by the same resistance through the colony to the Nostoc filaments in both terrestrial and aquatic habitats At high irradiance and twice daily watering growth of N flagelliforme was doubled in CO 2 enriched air 1500 ppm compared with atmospheric air 350 ppm at the time Gao and Yu 2000 The realized photosynthetic rate of N commune was the same in stirred air saturated water of 1 m m DIC 0 98 m m HCO 3 0 02 m m CO 2 as in atmospheric air with 0 02 m m CO 2 Sand Jensen and Jespersen 2012 Thus the optimal habitat of N commune could be wet soils where water and inorganic carbon and nutrients are supplied to the lower colony surface while CO 2 and light are supplied to the upper surface This is the habitat in 1 cm deep water filled depressions in the limestone pavements where we have observed massive growth of N commune Sand Jensen et al 2010 Previous Section Next Section TOLERANCE OF ENVIRONMENTAL EXTREMES Freshwater Nostoc species do not experience extreme temperatures like those experienced by terrestrial species Active growth of N commune N pruniforme and N zetterstedtii is nonetheless confined to the same temperature range 0 35 C Temperature and desiccation tolerance The terrestrial and semiterrestrial species N commune and N flagelliforme are exceptional in their tolerance of alternating freezing and thawing and of desiccation and rehydration at varying temperatures in their open habitats located from the Arctic to tropical regions Li 1991 Sand Jensen and Jespersen 2012 In contrast the freshwater species N pruniforme and N zetterstedtii are not exposed to freezing and drying or to extreme temperatures in their temperate and sub Arctic environments Nonetheless it appears that active growth of all four species is confined to the same temperature interval between 0 and 35 C and that the fastest growth takes place around 25 C Møller et al 2014 Both N commune and N flagelliforme are widely distributed species in arid and semiarid bare land throughout the world Li 1991 Dodds et al 1995 Nostoc commune survives annual temperature ranges of 60 to 25 C under Arctic conditions and 30 to 50 C under temperate conditions Davey 1989 Sand Jensen and Jespersen 2012 Surface temperatures in the open habitats of N flagelliforme can reach 78 C in summer and 40 C in winter Li 1991 Both species can survive months or years of frost and drought as inactive desiccated crusts and within minutes to hours can reactivate ion exchange respiration photosynthesis and N fixation when water and suitable temperatures again become available Scherer et al 1984 Satoh et al 2002 Experiments with the temperate species N commune confirmed that photosynthesis and respiration were maintained after 36 h of desiccation of wet or already dry specimens at temperatures from 269 to 70 C while temperatures above 70 C led to death Sand Jensen and Jespersen 2012 During repeated daily cycles of drying for 18 h at 18 20 and 40 C and rewetting for 6 h at 20 C N commune retained its photosynthetic capacity at 18 and 20 C but died at 40 C presumably because of the greater costs of repair of macromolecules at this higher temperature which would generate stronger thermal damage than lower temperatures Sand Jensen and Jespersen 2012 In 24 day long experiments under permanently submerged conditions N commune also died at 45 C but survived at 35 C growth peaked at 25 C and declined at the lower temperatures of 15 and 5 C Møller et al 2014 Annual carbon fixation of rehydrated populations of N commune from an Antarctic dry valley was also a strong positive function of increasing temperatures above zero and up to 20 C the highest temperature tested Novis et al 2007 Thus there was no obvious sign of temperature adaptation or acclimation across geographical ranges Nostoc flagelliforme like other terrestrial Nostoc species Davey 1989 Dodds et al 1995 Sand Jensen and Jespersen 2012 showed great heat resistance when dry while it was more susceptible when wet or immersed Mei and Cheng 1990 The regular protein pigment structure of photosystem I complexes was destroyed at 70 and 80 C Hu et al 2005 Pretreatment of wet N flagelliforme at 65 C led to death and temperatures above 45 C stopped photosynthesis Mei and Cheng 1990 The exact temperature effect on survival of N commune and N flagelliforme apparently depends on the duration and frequency of heat exposure and on the length of time available for repair of cellular damage between heat exposures Sand Jensen and Jespersen 2012 Likewise a longer time was required for maximal photosynthesis and respiration to recover after rehydration of specimens subjected to extended periods of desiccation Scherer et al 1984 Potts 1994 2000 Qiu and Gao 1999 The recovery of rehydrated N flagelliforme was light dependent Gao et al 1998 and required potassium Qiu and Gao 1999 stressing that a suite of energy demanding metabolic processes involving expensive protein and lipid synthesis and various cellular repair systems restores cellular structure and catalytic capacity Angeloni and Potts 1986 Taranto et al 1993 Desiccation is not an issue for freshwater species of Nostoc except when they are washed ashore and temperature variability is also much lower in freshwater than in terrestrial habitats In Danish lakes for example the annual temperature range is typically 0 25 C in shallow water and 2 15 C in deep water Møller et al 2014 Nonetheless the temperature dependence of long term growth of N pruniforme and N zetterstedtii resembled that of hydrated N commune in that all three species grew fastest at 25 C and many times slower at 5 C while 45 C led to die off Fig 6 in Møller et al 2014 So while terrestrial Nostoc species possess extraordinary desiccation tolerance there is no major difference in the relationship of active growth with temperature in terrestrial and aquatic specimens from north temperate localities though we cannot rule out that different relationships of growth with temperature have evolved in specimens living under Arctic or tropical climates Because under temperate conditions temperature ranges between winter and summer are also profound it would not be a great surprise however if these relationships remained constant across geographical ranges High temperature requirements 20 C of maximum photosynthesis of N commune from an Antarctic valley with very short frost free periods support the latter suggestion pH and salt tolerance Being photosynthetic organisms capable of using both free CO 2 and HCO 3 at high efficiency all four Nostoc species can push pH in the external water above 10 5 and in some cases even above 11 Table 6 Exposure of rehydrated N commune to a pH gradient for 36 h also showed that it tolerated pH ranging from 3 to 10 while it died at pH 2 Sand Jensen and Jespersen 2012 Terrestrial Nostoc species should be able to survive exposure to rainwater of low pH typically 3 8 4 8 and only very acidic habitats receiving sulphuric acid from the oxidation of metal sulphides are likely to be below pH 3 Therefore when it comes to direct pH tolerance most terrestrial habitats should be open to colonization by Nostoc Although N commune can grow between garden tiles and on open sand soils fed by rainwater it appears to prefer clay soils and calcareous rocks of high pH perhaps because available HCO 3 can support photosynthesis during prolonged illumination The requirement of HCO 3 for photosynthesis of aquatic Nostoc is accompanied by a preference for a pH above 7 in the water because of the buffering and alkalinization effect of HCO 3 Thus at air saturation freshwaters with pHs of 6 5 7 5 and 8 5 have HCO 3 concentrations of 0 05 0 5 and 5 m m respectively Stumm and Morgan 1981 Because N commune and N flagelliforme often grow in arid habitats with salt accumulation they must be tolerant Indeed N commune retained its photosynthetic capacity upon exposure to alkaline freshwater enriched with NaCl to 20 g kg 1 but not 30 g kg 1 as in oceanic water Sand Jensen and Jespersen 2012 The closely related N flagelliforme was also salt resistant but photosynthesis respiration and photosystem II activity declined upon exposure to 12 g NaCl kg 1 Ye and Gao 2004 Yong Hong et al 2005 Salt resistance is probably based on the formation of sucrose and trehalose both of which accumulate under desiccation and exposure to low salt concentrations Sakamoto et al 2009 and therefore play a dual role Tolerance of freezing and desiccation is extraordinary while salt tolerance is modest Other cyanobacteria are more salt tolerant because of the synthesis of glucosylglycerol in species of moderate tolerance and glycine betaine and glutamate betaine in species showing high tolerance Mackay et al 1984 Previous Section Next Section ECOLOGICAL ADAPTATIONS AND STRATEGIES Colonial Nostoc species live in resource poor environments and succumb in competition with tall macroalgae and plants under richer conditions All four colonial Nostoc species discussed here live in resource poor environments with a limited supply of water and inorganic nutrients on land and a limited supply of nutrients and DIC under water Phosphorus could be a limiting nutrient for growth but experimental tests are lacking All species can fix elemental N 2 but this is a costly process that requires a rare co factor molybdenum In suspension culture with N flagelliforme the variable availability of nitrogen and phosphorus influences the production of new cells and extracellular polysaccharides Fei et al 2012 The terrestrial N commune and N flagelliforme grow on nutrient poor sparsely vegetated or bare soils and rock surfaces that alternate between being wet and dry From April to September on the open limestone alvar on Öland Sweden measurements of humidity and temperature suggested that populations of N commune were rehydrated and active at least 26 of the time Sand Jensen and Jespersen 2012 From October to March populations were probably active during larger parts of the frost free time Maximum recorded growth rates of N commune floating on water and exposed to atmospheric air under laboratory conditions were 0 050 0 056 d 1 at 15 25 C and markedly lower at 0 020 0 025 d 1 at 5 and 35 C Møller et al 2014 These growth rates correspond to doubling times of dry mass between 12 and 35 d Growth rates are intermediate when compared with the extremely low rates 0 0008 d 1 of oligotrophic N zetterstedtii and high rates 0 2 0 4 d 1 of nutrient demanding thin macroalgae e g Cladophora spp and Enteromorpha spp Sand Jensen and Borum 1991 Nielsen and Sand Jensen 1991 According to Grime s 1979 classification of plant growth strategies in relation to resource richness and disturbance the stress strategy S of N zetterstedtii is linked to resource poor stabile habitats the ruderal strategy R of thin green macroalgae is linked to resource richness and high disturbance and the competitive strategy C of thick macroalgae is linked to resource richness and low disturbance Resource poor highly disturbed habitats do not in Grime s concept support a viable strategy because the growth rate is very low when resources are limiting and disturbance leads to frequent loss of biomass thus preventing long term survival However N commune and N flagelliforme can survive disturbance by desiccation freezing and extreme temperatures with restricted biomass loss in a quiescent stage and possesses a viable strategy in the resource

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  • Ecophysiology of gelatinous Nostoc colonies: unprecedented slow growth and survival in resource-poor and harsh environments

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  • Ecophysiology of gelatinous Nostoc colonies: unprecedented slow growth and survival in resource-poor and harsh environments
    exchange of DIC and oxygen Colonies were incubated at three DIC levels containing initially 0 99 m m circles 0 29 m m triangles and 0 10 m m squares After Sand Jensen et al 2009 b reproduced with permission of the Association for the Sciences of Limnology and Oceanography Inc View larger version In this window In a new window Download as PowerPoint Slide Fig 4 Mean net photosynthesis s d of four replicates of small 0 18 g FM medium 0 84 g FM and large 2 71 g FM spherical colonies of N pruniforme as a function of external DIC concentration 95 HCO 3 The apparent half saturation constant for small medium and large colonies was 0 78 0 78 and 1 24 m m HCO 3 the initial linear slope of net photosynthesis at low limiting DIC concentration was 319 305 and 197 nmol O 2 cm 2 h 1 1 mmol DIC L 1 1 and photosynthesis extrapolated to zero DIC was 55 72 and 164 nmol O 2 cm 2 h 1 From Raun 2006 View larger version In this window In a new window Download as PowerPoint Slide Fig 5 Mean DIC uptake during photosynthesis in high light as a function of mean DIC concentration in the water for N commune N pruniforme and N zetterstedtii Sources N commune K Sand Jensen unpubl data N pruniforme Raun et al 2009 N zetterstedtii Sand Jensen et al 2009 b The Author 2014 Published by Oxford University Press on behalf of the Annals of Botany Company All rights reserved For Permissions please email journals permissions oup com Related articles ContentSnapshots Content Snapshots Ann Bot 2014 114 1 i iii doi 10 1093 aob mcu136 Extract Full Text HTML Full Text PDF Previous Next Article Table of Contents This Article Ann Bot 2014 114 1 17 33 doi 10 1093 aob mcu085 Abstract Free Free Figures Free Full Text HTML Free Full Text PDF Free Classifications Invited Review Services Article metrics Alert me when cited Alert me if corrected Alert me if commented Find similar articles Similar articles in Web of Science Similar articles in PubMed Add to my archive Download citation Request Permissions Responses Submit a response No responses published Citing Articles Load citing article information Citing articles via CrossRef Citing articles via Scopus Citing articles via Web of Science Citing articles via Google Scholar Google Scholar Articles by Sand Jensen K Search for related content PubMed PubMed citation Articles by Sand Jensen K Agricola Articles by Sand Jensen K Related Content Related articles in this journal Ecology Load related web page information Share Email this article CiteULike Delicious Facebook Google Mendeley Twitter What s this Search this journal Advanced Current Issue February 2016 117 2 Alert me to new issues The Journal About this journal Annals of Botany Collections AoB article attracts media coverage We are mobile find out more Journals Career Network Published on behalf of The Annals of Botany Company Impact factor

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  • Plant functional types in Earth system models: past experiences and future directions for application of dynamic vegetation models in high-latitude ecosystems
    case for model based simulations of past current and future distribution of vegetation Conclusions Models that incorporate the PFT concept predict many of the emerging patterns of vegetation change in tundra and boreal forests given known processes of tree mortality treeline migration and shrub expansion However representation of above and especially below ground traits for specific PFTs continues to be problematic Potential solutions include developing trait databases and replacing fixed parameters for PFTs with formulations based on trait co variance and empirical trait environment relationships Surprisingly despite being important to land atmosphere interactions of carbon water and energy PFTs such as moss and lichen are largely absent from DVMs Close collaboration among those involved in modelling with the disciplines of taxonomy biogeography ecology and remote sensing will be required if we are to overcome these and other shortcomings Key words Plant functional types PFT Earth system model ESM Arctic tundra biogeography dynamic vegetation models global change plant traits high latitude ecosystem Published by Oxford University Press on behalf of the Annals of Botany Company 2014 This work is written by a US Government employee s and is in the public domain in the US Related articles ContentSnapshots Content Snapshots Ann Bot 2014 114 1 i iii doi 10 1093 aob mcu136 Extract Full Text HTML Full Text PDF Previous Next Article Table of Contents This Article Ann Bot 2014 114 1 1 16 doi 10 1093 aob mcu077 First published online May 2 2014 Abstract Free Free Figures Free Full Text HTML Free Full Text PDF Free All Versions of this Article mcu077v1 114 1 1 most recent Classifications Invited Review Services Article metrics Alert me when cited Alert me if corrected Alert me if commented Find similar articles Similar articles in Web of Science Similar articles in PubMed Add to my archive Download citation Request Permissions Responses Submit a response No responses published Citing Articles Load citing article information Citing articles via CrossRef Citing articles via Scopus Citing articles via Web of Science Citing articles via Google Scholar Google Scholar Articles by Wullschleger S D Articles by Xu X Search for related content PubMed PubMed citation Articles by Wullschleger S D Articles by Epstein H E Articles by Box E O Articles by Euskirchen E S Articles by Goswami S Articles by Iversen C M Articles by Kattge J Articles by Norby R J Articles by van Bodegom P M Articles by Xu X Agricola Articles by Wullschleger S D Articles by Xu X Related Content Related articles in this journal Ecology Modelling Load related web page information Share Email this article CiteULike Delicious Facebook Google Mendeley Twitter What s this Search this journal Advanced Current Issue February 2016 117 2 Alert me to new issues The Journal About this journal Annals of Botany Collections AoB article attracts media coverage We are mobile find out more Journals Career Network Published on behalf of The Annals of Botany Company Impact factor 3 654 5 Yr impact factor 4 338 Eigenfactor

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  • Plant functional types in Earth system models: past experiences and future directions for application of dynamic vegetation models in high-latitude ecosystems
    These changes and how they affect litter decomposition as well as the extent to which relationships between litter chemistry and decomposition are decoupled in a future climate Aerts et al 2012 need to be considered in DVMs Similarly various studies have shown highly species specific impacts on methane emissions also within Arctic and boreal PFTs Ström and Christensen 2007 Koelbener et al 2010 Thus to obtain robust estimates of regional methane emissions which is an important target of these vegetation models Melton et al 2013 quantifying within PFT differences may be crucial Even treeline advancement has been shown to be highly variable within PFTs Elmendorf et al 2012 a and for this purpose inclusion of variability within morphological and physiological traits may provide new quantitative insights View larger version In this window In a new window Download as PowerPoint Slide Fig 3 Variation in specific leaf area and leaf nitrogen concentration per unit dry mass for boreal herbs grasses shrubs and trees The points in grey global are for species from a larger worldwide set of observations The data for herbs grasses shrubs and trees present species mean trait values for 599 plant species and 4483 species worldwide form the TRY database of plant traits Kattge et al 2011 Note that the x and y axis are both plotted on a log scale Current PFT classifications and model implementations often neglect root traits and instead focus on above ground properties and processes as evidenced by common PFT terminology e g evergreen deciduous and C 3 C 4 grasses However the interaction of plant roots with the surrounding soil environment has been shown to exert important controls over the effect of changing climatic conditions on Arctic and boreal ecosystems Hartley et al 2012 A recent review indicates that mean below ground biomass of PFTs in Arctic tundra can be between two and seven times as much as above ground biomass Root traits including morphology chemistry porosity exudation rates depth distribution and mycorrhizal colonization can differ strongly within the same life form Pohl et al 2011 and can affect ecosystem carbon and nutrient cycling Chapin et al 1993 Nowinski et al 2008 Keuper et al 2012 and methane emissions Ström et al 2012 The poor representation of root traits in PFT classifications and their parameterization stems directly from the difficulty of measuring root properties especially in cold water saturated high latitude ecosystems A potential near term solution to overcoming a lack of information on root traits across PFTs would be to employ an economics spectrum perspective to vegetation dynamics Freschet et al 2010 Such a view has the benefit that co variation among above and below ground plant traits e g Craine et al 2003 Freschet et al 2010 McCormack et al 2012 may allow estimation of root traits for PFTs where very few data are available Trait variability above and below ground can be incorporated into DVMs in multiple ways One approach would be to vary parameters within PFTs as a function of environmental variables Such an approach has the rationale that community or PFT mean trait values are selected by environmental conditions thus causing trait convergence This selection by the environment is expressed in empirical trait environment relationships which have shown globally consistent patterns relating leaf functional traits to climate Wright et al 2005 soil fertility Ordoñez et al 2009 or combinations thereof e g Ordoñez et al 2010 van Ommen Kloeke et al 2012 Incorporation of empirical trait environment relationships into the JSBACH DGVM which is part of the Max Planck Institute Earth system model MPI ESM indicated major consequences of trait variability on vegetation and carbon dynamics for the current climate Verheijen et al 2013 Similar relationships may be derived specifically or otherwise modified from existing correlations for northern high latitude ecosystems within DVMs Environmental drivers known to be important to Arctic and boreal PFTs including the number of frost days but also soil moisture and nutrient availability are likely to be essential for refining mechanistic based models of Arctic ecosystems and for linking biogeochemical cycling models to vegetation dynamics models in an integrated coupled land climate model framework for both regional and global scales Such trait responses could be inferred for example from observations across gradients of permafrost degradation Schuur et al 2009 A working hypothesis is that permafrost degradation causes a change in water and nitrogen availability and distribution that will drive changes in trait expression and PFT distribution across the landscape The data needed to test this hypothesis and develop the functional relationships for modelling include seasonal variation in active layer nitrogen availability plant soil feedbacks that alter carbon nitrogen cycling and nitrogen availability plant utilization of available nitrogen including seasonal dynamics root distribution and nitrogen fixation and root distribution of plants in relation to water A combination of empirical data and insights generated via a model of carbon nitrogen interactions Xu et al 2012 could help clarify and establish the importance of variation in nitrogen acquisition and allocation strategies within and between PFTs in areas of thawing permafrost Another approach is to incorporate trait variability based on trade offs and evolutionary rules to determine the survival of trait combinations within a given PFT for a suite of environmental conditions Kleidon and Mooney 2000 Scheiter and Higgins 2009 Information on trait trade offs including co varying above and below ground traits Freschet et al 2010 Sloan et al 2013 and on trait impacts on carbon fluxes in high latitudes Cornelissen et al 2007 Freschet et al 2011 is already available With this type of information the first semi quantitative models based on eco evolutionary principles for northern high latitude ecosystems could be constructed For this approach to operate quantitatively however a complete quantitative understanding of allometric relationships for Arctic and boreal PFTs would be required i e to predict differences in above and below ground biomass Moreover an expanded understanding of the carbon or energy costs associated with high latitude adaptations e g cold tolerance would be necessary Such insights are beginning to emerge Lenz et al 2013 A comprehensive understanding of how different trade offs relate to different PFT architectures e g between tussock and non tussock graminoid growth forms would provide additional insights to incorporate into PFTs While such information is partially available it has not yet been compiled in an eco evolutionary based optimality approach Finally a more radical approach would be to abandon PFTs altogether and apply optimality principles Pavlick et al 2013 or empirical relationships to predict trait prevalence and vegetation distributions Reu et al 2011 a b Neither of these approaches however has been implemented in Arctic and boreal DVMs Nonetheless it seems feasible to incorporate variable trait approaches for the modelling of vegetation dynamics and carbon and nutrient cycling in northern high latitude ecosystems Previous Section Next Section VALIDATION AND BENCHMARKING OF PREDICTED VEGETATION PATTERNS While multiple efforts are underway to enhance the PFT representation within local regional and global models data on the spatial extent of vegetation types are required for benchmarking and validation purposes Sitch et al 2003 Kelley et al 2013 Numerous efforts over the past decades to document the geographic patterns of Arctic tundra vegetation at scales ranging from the plot to circumpolar have proven extremely useful benchmarks for predicting changes in Arctic tundra PFTs Kaplan and New 2006 Probably the most comprehensive effort over the broadest spatial extent was the development of the Circumpolar Arctic Vegetation Map CAVM Team 2003 The CAVM with polygons mapped at the 1 7 5 million scale contains five broad categories sub divided into a total of 15 vegetation mapping units with the PFT concept driving the development of these distinct vegetation sub units The five physiognomic categories were barrens graminoid tundra prostrate shrub tundra erect shrub tundra and wetlands distinguished by their dominant PFTs The sub divisions of each of these broader categories were also determined by the relative abundances of the PFTs For example graminoid tundra was divided into four sub categories that included communities dominated by rushes grasses tussock sedges and non tussock sedges Some Arctic tundra vegetation maps have been developed at finer resolutions e g regional continental scale Muller et al 1999 used Landsat Multi Spectral Scanner imagery to develop a map of Arctic tundra vegetation types for northern Alaska at a resolution of 100 m The vegetation classes were defined by the dominant PFTs and include moist graminoid prostrate shrub tundra moist tussock graminoid dwarf shrub tundra wet graminoid tundra dry prostrate shrub tundra and moist dwarf shrub tussock graminoid tundra For northern Canada Gould et al 2003 developed a tundra vegetation map at a finer scale 1 4 000 000 than the CAVM using a variety of data sources including the Advanced Very High Resolution Radiometer AVHHR colour infrared image basemap The vegetation map produced in this effort included 17 vegetation types and there was also an aggregated map of the biogeography of 11 PFTs These PFTs included lichens bryophytes cushion forbs three graminoid types and six shrub types Therefore both the CAVM and these regional scale PFT maps provide some excellent spatial and eventually temporal benchmarks for assessing PFT dynamics Similar efforts are underway to map vegetated wetlands throughout Arctic and boreal regions of Alaska although the current location types and extents of wetlands e g fens and bogs in high latitude ecosystems are uncertain Whitcomb et al 2009 As the examples just described suggest a variety of remote sensing products are available for benchmarking model simulations The extensive coverage in space and time by satellite and airborne imaging provides an unparalleled set of Earth observational data for such purposes Airborne in situ measurements can also provide complementary value added data However the available data products from the presently operating satellite sensors are not always readily usable for model benchmarking and validation since DVMs often track variables not directly measured by remote sensors e g net ecosystem exchange and active layer depth Hence additional processing of the directly measured remote sensing data is needed to convert spectral information into key model variables such as gross or net primary productivity Additionally several technical issues pose significant challenges to the production of remote sensing data sets useful for comparison with model results including resolution mismatches between sensors and models orbital constraints on timing and frequency of observations difficulties with atmospheric corrections and obscuring of surface properties by clouds and snow cover Some of these issues are more prominent in high latitude ecosystems and would potentially increase uncertainties when using remote sensing for benchmarking and validation of high latitude DVMs In addition to using existing spatially explicit maps for model benchmarking and validation several networks across the Arctic and boreal region are also poised to provide data for model parameterization and initialization Investigators at a number of co ordinated networks are collecting site specific data on plant species composition leaf area index and biomass of various PFTs One of the most comprehensive extensive and long running networks is the International Tundra Experiment ITEX Walker et al 2006 Elmendorf et al 2012 a b The ITEX is a collection of sites in Arctic and alpine tundra with a common warming experiment using passive warming open top chambers and a consistent sampling protocol largely point frame data collection across locations Thus for more than two dozen sites throughout the Arctic data exist on the absolute and relative abundances of various tundra PFTs obtained through non destructive sampling As an example Oberbauer et al 2013 used 12 sites in the ITEX network to examine the phenological responses of graminoids forbs and deciduous and evergreen shrubs to interannual climate variability Over the past decade or more a number of research projects have provided the opportunity for the development of two tundra wide transects the North American and the Eurasian Arctic transects Walker et al 2012 Each of these two transects spanned the full latitudinal gradient of the Arctic across all five tundra sub zones CAVM Team 2003 and there are comprehensive and consistent data on floristic characteristics leaf area index and above ground biomass across 13 sites Alaska Canada and Siberia for six PFTs i e mosses lichens graminoids forbs evergreen shrubs and deciduous shrubs Walker et al 2012 Finally data on PFTs have been collected from a number of sites some of which also have ITEX installations that could be used for additional benchmarking locations including but not limited to Toolik Lake Long Term Ecological Research station Low Arctic Alaska USA Barrow Environmental Observatory High Arctic Alaska USA Devon Island Alexandria Fjord Canadian Arctic Zackenberg Ecological Research Operations north east Greenland Abisko Scientific Research Station Sweden Ny Ålesund Svalbard and Cherskii Field Station north east Siberia Russia With regard to validation of modelled projections of changes in tundra PFTs the aforementioned ITEX network may be the most useful set of spatially explicit information Data from ITEX locations with passive warming experiments of different durations have been used to compare with model results In fact output of vegetation dynamics from the ArcVeg model Epstein et al 2004 was compared with observed vegetation changes from a synthesis of ITEX sites Walker et al 2006 In a recent study Elmendorf et al 2012 b synthesized results from 61 experimental warming studies with durations of up to 20 years and found that shrubs increased in response to warming essentially where average temperatures were already high whereas graminoids increased with warming in the colder sites indicating regional differences in PFT responses to warming These kinds of results will probably be most useful in validating simulation model output of PFT dynamics In addition to the passive warming treatments of the ITEX network other sites scattered throughout the Arctic have hosted other passive as well as active warming experiments that could be used for PFT modelling validation e g Buizer et al 2012 Henry et al 2012 Kaarlejarvi et al 2012 Zamin and Grogan 2012 Campioli et al 2013 Sharp et al 2013 Sistla et al 2013 Several experimental studies are currently underway including soil warming and water table manipulations near the Bonanza Creek Experimental Forest in interior Alaska where an emphasis is being placed on understanding boreal forest dynamics in a changing climate Turetsky et al 2008 Kane et al 2013 These studies offer additional insights into the responses of different PFTs to environmental change i e disturbance regimes and the use of those data for model parameterization and validation Previous Section Next Section RECOMMENDATIONS AND CONCLUDING REMARKS Plant functional types have offered both the biologist and the modeller a tractable scheme to represent plant diversity and associated function in models of the terrestrial biosphere Although alternatives or refinements have been suggested Pavlick et al 2013 Scheiter et al 2013 and may emerge as new avenues for model improvement the PFT concept is currently well integrated into DVMs and thus is likely to persist as an approach to reduce biological complexity in models for the foreseeable future As the community continues to rely on PFTs to represent plant species and their dynamics in models several advancements are needed including 1 PFT classification especially related to the integration of remote sensing mapping and validation of current and projected patterns of vegetation distribution 2 inclusion of appropriate PFTs in regional models paying close attention to trait based characteristics that influence biogeochemical and biophysical functioning of ecosystems 3 trait identification database compilation and dynamic parameterization of PFTs for above and below ground properties and processes and 4 data development for model benchmarking and validation In addition we advocate for model development to improve the representation of competition among PFTs successional dynamics and disturbance Several researchers have recently raised important questions about the need to better integrate PFT classification activities with vegetation mapping and model validation efforts using remote sensing and ground truthing approaches Sun and Liang 2007 and Sun et al 2008 emphasized that because of species diversity and variation in spectral characteristics accurate monitoring and mapping of PFTs is a difficult task and as a result no satisfactory methodology exists for the extraction of PFT classifications from satellite observations This often leads to a disconnection between field observations and model projections A possible solution to this dilemma may be classification of PFTs consistent with satellite sensors and their derived products Poulter et al 2011 recognized this and showed how major sources of uncertainty in a widely used DVM LPJmL could be addressed by cross walking or reclassifying land cover types to broader PFT categories based on land cover information for three satellite sensors EOS MODIS SPOT4 VEGETATION and ENVISAT MERIS Additional efforts that facilitate a close collaboration among modellers plant geographers and those who acquire and process remote sensing data sets should be encouraged An excellent illustration of this is reflected in the recent concept of optical type as a means to link structural physiological and phenological traits with optical properties of PFTs Ustin and Gamon 2010 Assessing the connections among these traits and evaluating their utility in DVMs would benefit from the further involvement of plant ecologists and modellers who could bring additional insights and perspectives to the analysis of such a potentially novel approach Despite the utility of remote sensing to the identification and mapping of PFTs at regional to global scales there are limits to this approach Satellite and aircraft based imaging tends to neglect important PFTs especially those encompassing non vascular species This occurs despite knowledge that non vascular plant types and communities play a vital role in ecosystem function especially in northern latitudes For example Turetsky et al 2012 emphasized the important role that mosses play in the structure and function of Arctic and boreal ecosystems a conclusion that was similarly echoed through model evaluation Lawrence and Slater 2008 Lawrence et al 2008 Engstrom et al 2006 uniquely and appropriately added non vascular vegetation mosses to the BIOME BGC model to simulate evapotranspiration in Arctic coastal plain systems Mosses and lichens have also been incorporated as PFTs into the Terrestrial Ecosystem Model TEM and parameterized using site specific knowledge Euskirchen et al 2009 thus this model and a few others e g ArcVeg Epstein et al 2000 can simulate the functional role of these PFTs for permafrost stability and grazing Yu et al 2009 2011 Lichens in particular are crucial for understanding vegetation herbivore interactions as they are a main source of winter nutrition for grazing animals in tundra Thompson and McCourt 1981 Johnstone et al 2002 However while models have begun to simulate lichen abundance and other forage species important for grazing animals the feedback on how grazing controls plant growth and PFT abundance has not been taken into account by models Zamin and Grogan 2013 Furthermore when short stature PFTs such as mosses and lichens are incorporated into models it is important to incorporate competition among PFTs due to light availability since increasing abundance of taller vascular plants may decrease the amount of light available to mosses and lichens thereby causing them to decline Cornelissen et al 2001 Global data sets such as the TRY initiative Kattge et al 2011 currently contain little information on non vascular cryptogams i e bryophytes and lichens despite their diversity in species functions and ecosystem effects This deficiency must be overcome and is probably one that also needs to be addressed alongside challenges of identifying non vascular PFTs via remote sensing The geographical distribution of plants and hence spatial patterns of PFTs is determined by plant plant competition mediated by climate soils and various forms of disturbance including fire permafrost thaw insects and disease In a recent review Scheiter et al 2013 outlined a series of deficiencies in DVMs and how those could be addressed assuming that next generation models adopted principles from community assembly and coexistence theories used in ecology Several of those deficiencies focused on reproduction competition and the consequences of resource availability e g water or nutrients on the distribution of vegetation based on how plants with different trait combinations perform under a particular environmental condition e g temperature light and CO 2 and disturbance regimes e g fire and windthrow For the Arctic and boreal regions competition successional dynamics and disturbance are important considerations for the trajectories of ecosystems in a changing climate yet DVMs are just now beginning to capture these interactions in high latitude ecosystems and elsewhere Haverd et al 2013 Kantzas et al 2013 Furthermore understanding resource use and acquisition across broad categories of plant species remains a key challenge in modelling competition among PFTs For example to model competition for soil water among PFTs information on rooting depth and root mass in a given layer of soil is important but little information is available on rooting characteristics for high latitude PFTs Changes in PFTs following disturbance and subsequent succession during recovery may also be difficult to capture particularly for Arctic and boreal vegetation transitions under conditions of for example fire and thermokarst While we have a general understanding of the changes in vegetation types likely to occur we often do not know the relative abundance of PFTs within recently disturbed ecosystems and indeed some of these may be unique no analogue communities e g Williams and Jackson 2007 Thus it appears that more information is needed on traits that determine the competitive behaviour of PFTs and on how these ecosystems develop during succession following a disturbance if we are to make reliable projections of carbon nutrient water and energy budgets for high latitude ecosystems Many of the deficiencies we have identified can only be resolved through the availability of regional and global data sets of plant characteristics traits and trait based strategies that can be used within the PFT framework Fortunately the last few years have seen an increase in trait identification data compilation and inventories and analyses of those data sets for among other uses parameterization of PFTs across a wide range of above and to a lesser extent below ground properties and processes The TRY database is especially noteworthy in this regard as a global inventory of plant traits many of which have application in the parameterization of PFTs Kattge et al 2011 This initiative began as a modest effort but has quickly grown into a data repository that currently contains almost 5 million trait entries for 80 000 of the world s 300 000 plant species The global trait database has been used in many ways not only to assign traits to PFTs used in models McMahon et al 2011 but also to develop hypotheses that might lead to a replacement of fixed PFT parameters with more continuous trait variables or spectra Kattge et al 2011 Additional contributions to the TRY initiative from existing databases and new measurements are needed however to encompass the tremendous global diversity in traits for vascular and non vascular plants For example TRY currently contains little information on non vascular cryptogams i e bryophytes and lichens despite their diversity in species functions and ecosystem effects Root traits in particular are also largely missing from the database with coarse measures of rooting depth being the primary below ground variable root distribution as a trait is available for only 0 05 of the vascular plant species Kattge et al 2011 This must be improved as well as additional data collected and contributed on root traits including a range of root structure and functional characteristics One such attempt to compile and analyse existing root data from Arctic tundra ecosystems and to identify knowledge gaps that could be filled by future studies is already underway An expanded set of traits and their availability for inclusion into models will greatly enhance the representation of biological processes feedbacks and interactions in terrestrial ecosystems Recent observations and historical information suggest that high latitude terrestrial ecosystems are experiencing rapid and unprecedented changes in climate Hinzman et al 2013 Knowing how the structure and function of Arctic and boreal ecosystems will respond to persistent climatic change is a significant challenge one in which vegetation plays a central albeit uncertain role Models that incorporate the PFT concept can provide valuable insights into the emerging patterns of vegetation change in tundra and boreal forests given known processes of tree mortality treeline migration and shrub expansion However DVMs require consistent evaluation based on knowledge provided by the plant biologist and others working with modellers to improve representation of critical processes In this review we have identified a few of those across diverse scientific disciplines of taxonomy biology biogeography remote sensing data management and modelling Progress has been made in recent years to improve representation of vegetation dynamics and the inter relationships among vegetation biogeochemistry and feedbacks to climate Much work remains and given the sensitivity of high latitude ecosystems to warming temperatures steps should be taken to assemble expertise across many fields and conduct the collaborative research necessary to reduce uncertainties in DVMs and ultimately ESMs Previous Section Next Section ACKNOWLEDGEMENTS This research was sponsored by the US Department of Energy Office of Science Biological and Environmental Research Program Oak Ridge National Laboratory is managed by UT Battelle LLC for the US Department of Energy under contract DE AC05 00OR22725 The Next Generation Ecosystem Experiments NGEE Arctic project is supported by the Office of Biological and Environmental Research in the DOE Office of Science The US Government retains and the publisher by accepting the article for publication acknowledges that the US Government retains a non exclusive paid up irrevocable world wide licence to publish or reproduce the published form of this manuscript or allow others to do so for US Government purposes Published by Oxford University Press on behalf of the Annals of Botany Company 2014 This work is written by a US Government employee s and is in the public domain in the US Previous Section LITERATURE CITED Aerts R van Bodegom PM Cornelissen JHC Litter stoichiometric traits of 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