DOI number:10.5194/bg-12-5339-2015
Abstract:Dynamic global vegetation models (DGVMs) typically rely on plant functionaltypes (PFTs), which are assigned distinct environmental tolerances andreplace one another progressively along environmental gradients. Fixedvalues of traits are assigned to each PFT; modelled trait variation alonggradients is thus driven by PFT replacement. But empirical studies haverevealed "universal" scaling relationships (quantitative trait variationswith climate that are similar within and between species, PFTs andcommunities); and continuous, adaptive trait variation has been proposed toreplace PFTs as the basis for next-generation DGVMs.Here we analyse quantitative leaf-trait variation on long temperature andmoisture gradients in China with a view to understanding the relativeimportance of PFT replacement vs. continuous adaptive variation within PFTs.Leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC) andnitrogen content of dry matter were measured on all species at 80 sitesranging from temperate to tropical climates and from dense forests todeserts. Chlorophyll fluorescence traits and carbon, phosphorus andpotassium contents were measured at 47 sites. Generalized linear models wereused to relate log-transformed trait values to growing-season temperatureand moisture indices, with or without PFT identity as a predictor, and totest for differences in trait responses among PFTs.Continuous trait variation was found to be ubiquitous. Responses to moistureavailability were generally similar within and between PFTs, but biophysicaltraits (LA, SLA and LDMC) of forbs and grasses responded differently fromwoody plants. SLA and LDMC responses to temperature were dominated by theprevalence of evergreen PFTs with thick, dense leaves at the warm end of thegradient. Nutrient (N, P and K) responses to climate gradients weregenerally similar within all PFTs. Area-based nutrients generally declinedwith moisture; Narea and Karea declined with temperature, butParea increased with temperature.Although the adaptive nature of many of these trait-climate relationships isunderstood qualitatively, a key challenge for modelling is to predict themquantitatively. Models must take into account that community-level responsesto climatic gradients can be influenced by shifts in PFT composition, suchas the replacement of deciduous by evergreen trees, which may run eitherparallel or counter to trait variation within PFTs. The importance of PFTshifts varies among traits, being important for biophysical traits but lessso for physiological and chemical traits. Finally, models should takeaccount of the diversity of trait values that is found in all sites andPFTs, representing the "pool" of variation that is locally available forthe natural adaptation of ecosystem function to environmental change.
Discipline:Natural Science
First-Level Discipline:Ecology
Translation or Not:no
Included Journals:SCI