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Climate change is expected to modify plant assemblages in ways that will have major consequences for ecosystem functions. How climate change will affect community composition will depend on how individual species respond, which is likely related to interspecific differences in functional traits. The extraordinary plasticity of some plant traits is typically neglected in assessing how climate change will affect different species. In the Mongolian steppe, we examined whether leaf functional traits under ambient conditions and whether plasticity in these traits under altered climate could explain climate-induced biomass responses in 12 co-occurring plant species. We experimentally created three probable climate change scenarios and used a model selection procedure to determine the set of baseline traits or plasticity values that best explained biomass response. Under all climate change scenarios, plasticity for at least one leaf trait correlated with change in species performance, while functional leaf-trait values in ambient conditions did not. We demonstrate that trait plasticity could play a critical role in vulnerability of species to a rapidly changing environment. Plasticity should be considered when examining how climate change will affect plant performance, species' niche spaces, and ecological processes that depend on plant community composition., (© 2015 John Wiley & Sons Ltd.)

Adler et al. (Reports, 23 September 2011, p. 1750) reported "weak and variable" relationships between productivity and species richness and dispute the "humped-back" model (HBM) of plant diversity. We show that their analysis lacks sufficient high-productivity sites, ignores litter, and excludes anthropogenic sites. If corrected, the data set of Adler et al. would apparently yield strong HBM support.

Aims: Changes in precipitation patterns, such as the predicted increases in the frequency of climatic extremes, are likely to alter plant communities, but whether responses to drought or to wetter conditions respectively cause consistent, opposite responses is debated. Here, we assessed the response in biomass production and species diversity of water‐limited plant communities to the direction (increase or decrease) and magnitude (micro‐ and macro‐climatic effects) of changes in soil moisture. Location: We reciprocally translocated soils containing seed banks from two climates (semi‐arid and mediterranean) at a micro‐climatic (opposite slopes) and a macro‐climatic scale (between climates) in Chile. Results: Biomass production for the soils that were translocated from wetter to drier climates was unrelated to the available soil moisture. The lowest biomass was produced in the wettest climate on the wet slope. Biomass production increased after a translocation to the drier climate (representing the largest change in climate). Nonetheless, the highest overall biomass for the wet to dry translocation was produced on the mediterranean dry slope with intermediate soil moisture. However, on the same mediterranean dry slope, biomass was almost zero for soil translocated the other way round (from drier to wetter). Diversity after 24 months was unaffected by micro‐climatic change, but soils transplanted toward the drier climate yielded a plant community with increased diversity. Conclusion: Our results showed direction and magnitude of climate change but also the response factor that is studied matters to detect direction‐dependent responses; i.e., species richness had a linear and reversible response. However, the response of biomass depended on the origin of the transplanted material (soil and plant community), indicating history dependence (hysteresis). This emphasizes that responses to unidirectional climate manipulation experiments may not be able to capture the entire nature of the response of plant communities to climate change. [ABSTRACT FROM AUTHOR]

The relationship between competition and productivity in plant communities is unclear, and this is likely to be due to (1) a confusion in the literature between productivity and biomass, (2) the lack of studies assessing variation in competition in all combinations of biomass and productivity. We assessed the outcome of plant–plant interactions by removing the neighbors around five focal species in 14 herbaceous communities with contrasting biomasses and productivities: meadows with high biomass and productivity, heathlands with high biomass and low productivity, understory communities of deciduous forests with low biomass and high productivity and calcareous grasslands with low biomass and low productivity. Competition intensity was quantified with the relative interaction index (RII) calculated for both survival and growth of the transplanted targets assessed with the increase in leaf number. To examine which traits better explain variation in competition and what drives variation in diversity, we also quantified litter decomposition rate, species composition and diversity and six morphological traits related to plant size and growth rate for eight dominant species of each community. Our main questions were: (1) Is competition mostly related to biomass or productivity? (2) Which traits of the community dominants better explain variation in competition? (3) Is variation in competition and related traits correlated with variation in diversity? Competition for survival significantly increased with increasing community biomass (but not productivity). In addition, competition for survival increased with the size traits and competitive effects of the dominant species of the communities, whereas diversity decreased. Competition for growth also increased with increasing productivity, but only for high‐biomass communities. Additionally, the increase in competition for growth with increasing soil fertility, as measured with litter decomposition rate, was only due to an increase in target growth in plots without neighbors and was unrelated to community competitive effects and species diversity. The results of our study illustrate how the confusion between productivity and biomass could have contributed to the long‐standing debate on variation in competition along productivity gradients and its consequence for diversity. [ABSTRACT FROM AUTHOR]

How the relationship between species richness and productivity changes along environmental gradients remains poorly understood.We examined the context dependency of complementarity processes underpinning this relationship (biotic feedbacks, resource partitioning and facilitation) using the framework of Grime's (1973) humped‐back model. We considered several scenarios of variation in competition and facilitation along environmental gradients, either monotonic with the most common or intense facilitation at the most abiotically severe end of gradients or nonlinear with the strongest facilitation at intermediate positions along gradients.How competition shifts to facilitation along environmental gradients is a key for determining where the effect of species richness on productivity occurs. Based on the literature, the original Stress Gradient Hypothesis would likely predict that complementarity effects should be the greatest, or the most important, in the most abiotically stressful environments. Alternatively, both the 'collapse of facilitation' and the 'shift back to competition' scenarios predict that the highest overall complementary effects on productivity, not biomass, would most likely occur at intermediate positions along environmental stress gradients, but this might vary depending on the source of stress. This latter prediction is consistent with a great deal of literature on natural gradients of productivity and species richness.Synthesis. Our predictions illustrate the importance of better understanding the context dependency of complementarity processes and the key role of facilitation along environmental gradients to better focus conservation efforts where ecosystem functioning is more likely to be negatively affected by species loss, in particular in species‐rich communities. [ABSTRACT FROM AUTHOR]

The large majority of 'facilitation studies' focus on benefactor–beneficiary interactions. However, this may skew our view of the role of facilitation toward systems where it is most conspicuous, and perhaps toward harsh environments where discrete vegetation cover and pattern suggestive of facilitation are more common.Here we argue that a particular benefactor species is not required for facilitation to occur. Where vegetation cover is continuous, the community as a whole can ameliorate the abiotic conditions (community‐scale facilitative effect) and any species from the assembly experiencing stress (strain) could be facilitated. As a consequence, community‐scale facilitative effect might be generally common but often inconspicuous. Whether this community‐scale facilitative effect is influenced by particular characteristics of the vegetation cover is still largely unknown (e.g. biomass, species richness, functional composition and diversity).Expanding our research on facilitation beyond benefactor–beneficiary interactions and considering together the concept of community‐scale effect and strain might be key to progress our understanding of the general role of facilitation for species coexistence, ecosystem function, species distribution or climate change impact. [ABSTRACT FROM AUTHOR]

How plants allocate their biomass to different organs is essential to understanding plant adaptations and distributions. Overall, biomass allocation may follow fixed rules across taxa. They are also likely to exhibit substantial departure from these rules during ontogeny and in response to particular limiting factors to optimize their growth and maximize their survival. However, how plants adjust their allocation priorities depending on size and age across stress gradients remain largely unknown in wild populations.We examined ontogenetic variation in biomass allocation in Himalayan forb Potentilla pamirica across its 5,250–5,900‐m elevation range, between populations from dry steppe, wet alpine and cold subnival zone. We evaluated whether biomass allocation followed optimal partitioning or fixed allometric rules using organ mass in 1,019 individuals spanning 1–73 years.We found shifting biomass fractions with plant size and age, supporting the optimal partitioning theory. Young plants (<10 years) allocated similar proportions of biomass to leaves, stems and roots, intermediate‐aged plants (10–30 years) allocated more biomass to roots, while the oldest plants had 90% biomass in below‐ground stems.Major developmental processes including secondary thickening, branching and flowering begin 10–15 years earlier under more thermally favourable steppe conditions. Young steppe plants are larger than alpine and subnival plants, but these differences disappear in plants aged ~30, and the oldest alpine and subnival plants are larger than steppe plants.Plant age exerted significant control over biomass allocation after controlling for plant size. While in steppe plants the preference for stem biomass allocation increases with both size and age, for large alpine and subnival plants the stem prioritization decreases with age in favour of root and leaf mass fractions. We interpret root and leaf prioritization in older plants as a way to reduce carbon imbalances and the risk of frost damage to secure long life.Our analyses rejected ontogenetically fixed allometry and instead found high variation in biomass allocation depending on age, size and environment, supporting optimal partitioning theory. The uneven allocation of resources to different structures and functions during ontogenesis reflects plant adaptations to different levels of low‐temperature and water stress across species elevation range. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]