Responses of leaf traits to climatic gradients: adaptive variation versus compositional shifts

Abstract

Abstract. Dynamic global vegetation models (DGVMs) typically rely on plant functional types (PFTs), which are assigned distinct environmental tolerances and replace one another progressively along environmental gradients. Fixed values of traits are assigned to each PFT; modelled trait variation along gradients is thus driven by PFT replacement. But empirical studies have revealed "universal" scaling relationships (quantitative trait variations with climate that are similar within and between species, PFTs and communities); and continuous, adaptive trait variation has been proposed to replace PFTs as the basis for next-generation DGVMs. Here we analyse quantitative leaf-trait variation on long temperature and moisture gradients in China with a view to understanding the relative importance of PFT replacement vs. continuous adaptive variation within PFTs. Leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC) and nitrogen content of dry matter were measured on all species at 80 sites ranging from temperate to tropical climates and from dense forests to deserts. Chlorophyll fluorescence traits and carbon, phosphorus and potassium contents were measured at 47 sites. Generalized linear models were used to relate log-transformed trait values to growing-season temperature and moisture indices, with or without PFT identity as a predictor, and to test for differences in trait responses among PFTs. Continuous trait variation was found to be ubiquitous. Responses to moisture availability were generally similar within and between PFTs, but biophysical traits (LA, SLA and LDMC) of forbs and grasses responded differently from woody plants. SLA and LDMC responses to temperature were dominated by the prevalence of evergreen PFTs with thick, dense leaves at the warm end of the gradient. Nutrient (N, P and K) responses to climate gradients were generally similar within all PFTs. Area-based nutrients generally declined with moisture; Narea and Karea declined with temperature, but Parea increased with temperature. Although the adaptive nature of many of these trait-climate relationships is understood qualitatively, a key challenge for modelling is to predict them quantitatively. Models must take into account that community-level responses to climatic gradients can be influenced by shifts in PFT composition, such as the replacement of deciduous by evergreen trees, which may run either parallel or counter to trait variation within PFTs. The importance of PFT shifts varies among traits, being important for biophysical traits but less so for physiological and chemical traits. Finally, models should take account of the diversity of trait values that is found in all sites and PFTs, representing the "pool" of variation that is locally available for the natural adaptation of ecosystem function to environmental change.

Foliar pH, an emerging plant functional trait: Biogeography and variability across northern China

“…There was no significant difference in the LMM slopes among different plant life‐forms (Table ), and similar results have been found between other chemical traits and climate gradients (e.g., Meng et al, ). These results suggest that the response of foliar pH to the geographical and environmental factors was nearly consistent for woody plants and herbs.…”

Experimental evaluation of the robustness of the growth–stress tolerance trade‐off within the perennial grass Dactylis glomerata

“…As Kong and Henry () demonstrated that prior exposure to freezing stress enhanced Poa pratensis drought survival, some trait values are likely to benefit tolerance to both types of dehydration stresses. Our results showed that Mediterranean populations, which expressed summer dormancy, always had narrower leaves than other origins of D. glomerata , together with a high leaf dry matter content, that is traits values that have been previously mentioned as drought‐adaptive (Bartlett, Scoffoni, & Sack, ; Meng et al., ). Consistently, Mediterranean populations had higher summer drought survival, but this set of leaf traits was not associated with frost tolerance.…”

Polyploidy and the relationship between leaf structure and function: implications for correlated evolution of anatomy, morphology, and physiology in Brassica

“…Considered from the broadest functional perspective, the range of values we observed for F v '/F m ' in a single genus and constant environment (0.37–0.57) fall well within the range observed at a continental scale and across multiple vegetation types (0.14–0.89) [65]. More narrowly, compared to diploid parents species, the allotetraploids we examined had increased trait ranges that were largely caused by increased maximum trait values, despite relatively low rates of photosystem II gene retention following polyploidy in Glycine , Medicago , and Arabidopsis [66].…”