Nutrient effects on drought responses vary across common temperate grassland species

Drought and nutrient input are two main global change drivers that
threaten ecosystem function and services. Resolving the interactive
effects of human-induced stressors on individual species is necessary to
improve our understanding of community and ecosystem responses. This study
comparatively assessed how different nutrient conditions affect
whole-plant drought responses across 13 common temperate grassland
species. We conducted a fully factorial drought-fertilization experiment
to examine the effect of nutrient addition (nitrogen (N), phosphorus (P),
combined NP) on species' drought survival, and on drought
resistance of growth as well as drought legacy effects. Drought had an
overall negative effect on survival and growth, and the adverse drought
effects extended into the next growing season. Neither drought resistance
nor legacy effects exhibited an overall effect of nutrients. Instead, both
the size and the direction of the effects differed strongly among species
and between nutrient conditions. Consistently, species performance ranking
under drought changed with nitrogen availability. The idiosyncratic
responses of species to drought under different nutrient conditions may
underlie the seemingly contradicting effects of drought in studies on
grassland composition and productivity along nutrient and land-use
gradients – ranging from amplifying to dampening. Differential species’
responses to combinations of nutrients and drought, as observed in our
study, complicate predictions of community and ecosystem responses to
climate and land-use changes. Moreover, they highlight the urgent need for
an improved understanding of the mechanisms that render species more or
less vulnerable to drought under different nutrients.