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The degree to which elevated CO2 concentrations (e[CO2]) increase the amount of carbon (C) assimilated by vegetation plays a key role in climate change. However, due to the short‐term nature of CO2 enrichment experiments and the lack of reconciliation between different ecological scales, the effect of e[CO2] on plant biomass stocks remains a major uncertainty in future climate projections. Here, we review the effect of e[CO2] on plant biomass across multiple levels of ecological organization, scaling from physiological responses to changes in population‐, community‐, ecosystem‐, and global‐scale dynamics. We find that evidence for a sustained biomass response to e[CO2] varies across ecological scales, leading to diverging conclusions about the responses of individuals, populations, communities, and ecosystems. While the distinct focus of every scale reveals new mechanisms driving biomass accumulation under e[CO2], none of them provides a full picture of all relevant processes. For example, while physiological evidence suggests a possible long‐term basis for increased biomass accumulation under e[CO2] through sustained photosynthetic stimulation, population‐scale evidence indicates that a possible e[CO2]‐induced increase in mortality rates might potentially outweigh the effect of increases in plant growth rates on biomass levels. Evidence at the global scale may indicate that e[CO2] has contributed to increased biomass cover over recent decades, but due to the difficulty to disentangle the effect of e[CO2] from a variety of climatic and land‐use‐related drivers of plant biomass stocks, it remains unclear whether nutrient limitations or other ecological mechanisms operating at finer scales will dampen the e[CO2] effect over time. By exploring these discrepancies, we identify key research gaps in our understanding of the effect of e[CO2] on plant biomass and highlight the need to integrate knowledge across scales of ecological organization so that large‐scale modeling can represent the finer‐scale mechanisms needed to constrain our understanding of future terrestrial C storage. [ABSTRACT FROM AUTHOR]

Traits have been widely used in plant ecology to understand the rules governing community assembly, and to characterize primary strategies that define community structure and ecosystem properties. Relatively little is known as to whether the traits that are ecologically important at macroecological scales are either variable, or of consequence at fine scales within species. We measured trait variation within populations of the grassland plants Festuca ovina L. and Koeieria macrantha (Ledeb.) Schult., to test the hypothesis that fine-scale intraspecific trait variation drives local community structure. Both species showed large genotypic variation for all traits. Size-related traits of genotypes of K. macrantha observed under monoculture predicted their performance in model grassland communities that possessed both genetic and species diversity. The same correspondence was much weaker for the experimental population of F. ovina. A trade-off in allocation between shoot mass and relative allocation to reproduction was evident in the experimental population of F. ovina. Furthermore, both species showed evidence of a positive relationship between specific leaf area (SLA) and allocation to culm mass. This trait covariation indicates the existence of intraspecific trade-offs in life-history and growth strategies similar to those used to define primary plant strategies, which potentially buffers both species abundance and species coexistence against environmental challenges. Key words: community ecology, genotypic diversity, perennial grasses, primary plant strategies, species coexistence, trait trade-offs. En ecologie vegetale, on a largement utilise les caracteres genetiques pour comprendre les regles regissant l'assemblage des communaules, el pour caracteriser les strategies primaires definissant la structure des communautes el les proprietes des ecosystemes. On ne sait pas vraiment si les caracteres ecologiquement importants aux echelles macroecologiques sont variables ou encore une consequence aux fines echelles dans l'espece. Les auteurs ont mesure la variation de caracteres a l'interieur de populations de plantes des prairies, les Festuca ovina L. et Koeleria macrantha (Ledeb.) Schult., pour verifier l'hypothese a savoir que la variation intraspecifique des caracteres aux fines echelles guide la structure de la communaute locale. Les deux especes montrent une importante variation genotypique pour tous les caracteres. Les caracteres lies a la grandeur chez les genotypes du K. macrantha observes en monoculture permettent de predire leur performance dans des communautes herbacees modeles possedant a la fois une diversite genetique et specifique. La meme correspondance s'avere beaucoup plus faible chez la population experimentale du F. ovina. De plus, les deux especes montrent l'existence d'une relation positive entre la surface foliaire specifique (SLA) et l'allocation a la masse des chaumes. La co-variatiou de ces caracteres indique l'existence de compromis intraspecifiques dans le cycle vital et des strategies de croissance, semblables a celles utilisees pour definir les strategies primaires des plantes, lesquelles tamponnent potentiellement l'abondance des deux especes et leur coexistence devant des defis environnemeniaux. Mots-cles : ecologie des communautes, diversite genotypique, herbes perennes, strategie primaire des plantes, coexistence des especes, compromis entre caracteres. [Traduit par la Redaction], Introduction Life-history theory predicts that species growing in specific environments will share similarity in certain key traits or combinations of traits (MacLeod 1894; MacArthur and Wilson 1963; Caswell et al. [...]

Climate change will decrease precipitation and increase rainfall variability in eastern Mediterranean regions, with responses of plant communities largely uncertain. Here, we tested short‐term responses of dryland plant communities to contrasting rainfall regimes using reciprocal transplants of soil and seed banks. We exposed three annual plant communities to very different climatic conditions along a steep rainfall gradient. We tested for the role of climate versus community origin on community response and resistance. In parallel, we asked whether origin‐specific climatic adaptations predict compositional shifts across climates. Due to an extreme drought, all plants in the driest climate failed to reach maturity. For the remaining two community origins, the most dry‐adapted species in each community increased in dry climate and the wet‐adapted species increased in wet climate. Dry community origins showed large compositional shifts while maintaining stable plant density, biomass and species richness across climates. Conversely, wet communities showed smaller compositional shifts, but larger variation in biomass and richness. This asynchrony in species abundances in response to rainfall variability could maintain structural community stability. This, in combination with seed dormancy, has the ability to delay extinction in response to climate change. However, increasing occurrence of extreme droughts may, in the long‐term, lead to loss of wet‐adapted species. [ABSTRACT FROM AUTHOR]

Summary: Global warming and reduced precipitation may trigger large‐scale species losses and vegetation shifts in ecosystems around the world. However, currently lacking are practical ways to quantify the sensitivity of species and community composition to these often‐confounded climatic forces. Here we conducted long‐term (16 yr) nocturnal‐warming (+0.6°C) and reduced precipitation (−20% soil moisture) experiments in a Mediterranean shrubland. Climatic niche groups (CNGs) – species ranked or classified by similar temperature or precipitation distributions – informatively described community responses under experimental manipulations. Under warming, CNGs revealed that only those species distributed in cooler regions decreased. Correspondingly, under reduced precipitation, a U‐shaped treatment effect observed in the total community was the result of an abrupt decrease in wet‐distributed species, followed by a delayed increase in dry‐distributed species. Notably, while partially correlated, CNG explanations of community response were stronger for their respective climate parameter, suggesting some species possess specific adaptations to either warming or drought that may lead to independent selection to the two climatic variables. Our findings indicate that when climatic distributions are combined with experiments, the resulting incorporation of local plant evolutionary strategies and their changing dynamics over time leads to predictable and informative shifts in community structure under independent climate change scenarios. [ABSTRACT FROM AUTHOR]

The degree to which elevated CO2 concentrations (e[CO2]) increase the amount of carbon (C) assimilated by vegetation plays a key role in climate change. However, due to the short‐term nature of CO2 enrichment experiments and the lack of reconciliation between different ecological scales, the effect of e[CO2] on plant biomass stocks remains a major uncertainty in future climate projections. Here, we review the effect of e[CO2] on plant biomass across multiple levels of ecological organization, scaling from physiological responses to changes in population‐, community‐, ecosystem‐, and global‐scale dynamics. We find that evidence for a sustained biomass response to e[CO2] varies across ecological scales, leading to diverging conclusions about the responses of individuals, populations, communities, and ecosystems. While the distinct focus of every scale reveals new mechanisms driving biomass accumulation under e[CO2], none of them provides a full picture of all relevant processes. For example, while physiological evidence suggests a possible long‐term basis for increased biomass accumulation under e[CO2] through sustained photosynthetic stimulation, population‐scale evidence indicates that a possible e[CO2]‐induced increase in mortality rates might potentially outweigh the effect of increases in plant growth rates on biomass levels. Evidence at the global scale may indicate that e[CO2] has contributed to increased biomass cover over recent decades, but due to the difficulty to disentangle the effect of e[CO2] from a variety of climatic and land‐use‐related drivers of plant biomass stocks, it remains unclear whether nutrient limitations or other ecological mechanisms operating at finer scales will dampen the e[CO2] effect over time. By exploring these discrepancies, we identify key research gaps in our understanding of the effect of e[CO2] on plant biomass and highlight the need to integrate knowledge across scales of ecological organization so that large‐scale modeling can represent the finer‐scale mechanisms needed to constrain our understanding of future terrestrial C storage. [ABSTRACT FROM AUTHOR]

The degree to which elevated CO 2 concentrations (e[CO 2 ]) increase the amount of carbon (C) assimilated by vegetation plays a key role in climate change. However, due to the short-term nature of CO 2 enrichment experiments and the lack of reconciliation between different ecological scales, the effect of e[CO 2 ] on plant biomass stocks remains a major uncertainty in future climate projections. Here, we review the effect of e[CO 2 ] on plant biomass across multiple levels of ecological organization, scaling from physiological responses to changes in population-, community-, ecosystem-, and global-scale dynamics. We find that evidence for a sustained biomass response to e[CO 2 ] varies across ecological scales, leading to diverging conclusions about the responses of individuals, populations, communities, and ecosystems. While the distinct focus of every scale reveals new mechanisms driving biomass accumulation under e[CO 2 ], none of them provides a full picture of all relevant processes. For example, while physiological evidence suggests a possible long-term basis for increased biomass accumulation under e[CO 2 ] through sustained photosynthetic stimulation, population-scale evidence indicates that a possible e[CO 2 ]-induced increase in mortality rates might potentially outweigh the effect of increases in plant growth rates on biomass levels. Evidence at the global scale may indicate that e[CO 2 ] has contributed to increased biomass cover over recent decades, but due to the difficulty to disentangle the effect of e[CO 2 ] from a variety of climatic and land-use-related drivers of plant biomass stocks, it remains unclear whether nutrient limitations or other ecological mechanisms operating at finer scales will dampen the e[CO 2 ] effect over time. By exploring these discrepancies, we identify key research gaps in our understanding of the effect of e[CO 2 ] on plant biomass and highlight the need to integrate knowledge across scales of ecological organization so that large-scale modeling can represent the finer-scale mechanisms needed to constrain our understanding of future terrestrial C storage., (© 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Recent evidence indicates that grassland community structure and species diversity are influenced by genetic variation within species. We review what is known regarding the impact of intraspecific diversity on grassland community structure, using an ancient limestone pasture as a focal example. Two genotype-dependent effects appear to modify community structure in this system. First, the abundance of individual constituent species can depend upon the combined influence of direct genetic effects stemming from individuals within the population. Second, the outcome of localized interspecific interactions occurring within the community can depend on the genotypes of participating individuals (indicating indirect genetic effects). Only genotypic interactions are thought to be capable of allowing the long-term coexistence of both genotypes and species. We discuss the implications of these effects for the maintenance of diversity in grasslands. Next, we present new observations indicating that losses of genotypic diversity from each of two species can be predicted by the abundance of other coexisting species within experimental grassland communities. These results suggest genotype-specific responses to abundance in other coexisting species. We conclude that both direct and indirect genetic effects are likely to shape community structure and species coexistence in grasslands, implying tight linkage between fine-scale genetic and community structure.