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

Abstract

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.