Evidence for plant traits driving specific drought resistance. A community field experiment

Abstract

Drought is known to be a major bottleneck for woody-community recruitment. The species-specific resistance to drought and factors involved in its variation are of special interest to forecast community fate. We performed an experiment under natural field conditions from winter 2006 to end summer 2008 to investigate the structural responses of woody saplings to nine combinations of light (three habitats differing in plant cover: forest, shrubland, and open) and water (three climate scenarios: drier, current and wetter summers). Our working hypothesis is that plant strategies to cope with drought are determined by habitat characteristics and/or variation of plant traits, and that these different strategies may determine community composition and dynamics. Eight woody species with different life forms and successional stages (trees, mid-successional shrubs, and pioneer shrubs) were selected for the comparison, including therefore species representative of the entire woody community. We explored drought resistance at the population level (DS), the relations of the different morphological traits to DS, and the potential importance for plants of inter-specific trade-offs. DS ranged from 0% to 99% for the different species, depending on the habitat. Some structural traits were found to be related to DS: positively with total biomass and leaf mass ratio (LMR) and negatively with leaf area-root mass ratio (LARMR). Contrary to previous studies, the present work revealed no evidence of trade-offs, such as survival in forest vs. growth in open, or growth in forest vs. growth in open. Accordingly, some species with low DS values (Acer opalus and Pinus sylvestris) would be threatened under the future climate conditions, while species having structural characteristics to increase their resistance under expected dry years in coming decades (i.e., high LMR and total biomass or low LARMR, such as Quercus ilex and the shrub Cytisus scoparius) might enhance their recruitment probabilities. Thus, species-specific plant traits, and their effect on DS, may filter future community assemblages.