Post‐drought compensatory growth in perennial grasslands is determined by legacy effects of the soil and not by plants

Abstract

Summary Grasslands recovering from drought have repeatedly been shown to outperform non‐drought‐stressed grasslands in biomass production. The mechanisms that lead to the unexpectedly high biomass production in grasslands recovering from drought are, however, not understood. To disentangle plant‐intrinsic and plant‐extrinsic (soil) drought legacy effects on grassland recovery from drought, we designed a factorial field experiment where Lolium perenne plants that were exposed to either a 2‐month drought or to well‐watered control conditions were transplanted into control and drought‐stressed soil and rewetted thereafter. Drought and rewetting (DRW) resulted in negative drought legacy effects of formerly drought‐stressed plants (DRWp) compared with control plants (Ctrp) when decoupled from soil‐mediated DRW effects, with DRWp showing less aboveground productivity (−13%), restricted N nutrition, and higher δ13C compared with Ctrp. However, plants grown on formerly drought‐stressed soil (DRWs) showed enhanced aboveground productivity (+82%), improved N nutrition, and higher δ13C values relative to plants grown on control soil (Ctrs), irrespective of the plants' pretreatment. Our study shows that the higher post‐drought productivity of perennial grasslands recovering from drought relative to non‐drought‐stressed controls is induced by soil‐mediated DRW legacy effects which improve plant N nutrition and photosynthetic capacity and that these effects countervail negative plant‐intrinsic drought legacy effects.