Do interactions with neighbours modify the above-ground productivity response to drought? A test with two grassland species

• Target plants were exposed to drought in presence of con- or heterospecific neighbours.
• One species increased the susceptibility to negative effects of drought.
• Another species buffered the target's drought response.
• The effect of drought on the targets depended largely on the nature of the neighbours.

Natural systems are predicted to be exposed to more frequent and more intense drought events in the near future. Plant–plant interactions form an important part of the whole of mechanisms that govern the responses of plant species and communities to drought. The accuracy of predictions on ecosystem functioning would therefore be improved by determining when plant interactions need to be considered and how these interactions can drive species responses. In this study, we assessed the effect of neighbour plants on the drought response of a target plant. Two grassland species (Plantago lanceolata and Lolium perenne) were grown in the presence of either six conspecific or three conspecific and three heterospecific neighbours in sunlit growth chambers. They were subjected to drought by withholding water for 20 days. Regardless of the identity of the target plant, having P. lanceolata as a neighbour increased the susceptibility to negative drought effects on biomass production while L. perenne neighbours buffered the target's drought response. Our results therefore suggest that drought responses depended largely on the identity and the traits of the neighbours. Such findings demonstrate that current models to predict ecosystem functioning may be misleading by not sufficiently taking plant–plant interactions into account.