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.

We assessed drought resistance (i.e., the ability to maintain growth during drought), drought legacy effects (i.e., drought effects on growth persisting after the drought has subsided, sensu Vilonen et al. 2022) and drought survival responses in a fully factorial experimental design with four nutrient treatments combined with two moisture treatments (drought and irrigation treatment).

The experiment was conducted at the Ecological Botanical Garden of the University of Bayreuth, Germany in 2017–2019. The study was conducted on 13 common temperate, perennial grassland species (six grasses and seven forbs (among them three legumes)  that are common in the Biodiversity Exploratories plots and included a wide range of moisture and nutrient associations. 

We conducted a fully factorial drought-fertilization experiment in a common garden setting with four different nutrient conditions:

• nitrogen addition
• phosphorus addition
• combined NP addition
• unfertilized control (c)

Combined with two moisture treatments: 

• irrigated control
• drought treatment (56 days drought period)