Compensatory dynamics drive grassland recovery from drought

1. Grasslands are expected to experience droughts of unprecedented frequency and magnitude in the future. Characterizing grassland responses and recovery from drought is therefore critical to predict the vulnerability of grassland ecosystems to climate change. Most previous studies have focused on ecosystem responses during drought while investigations of post-drought recovery are rare. Few studies have used functional traits, and in particular bud or clonal traits, to explore the mechanisms underlying grassland responses to and recovery from drought.2. To address this issue, we experimentally imposed a four-year drought in a C-3-dominated grassland in northeastern China and monitored recovery for 3 years post-drought. We investigated the immediate and legacy effects of drought on total above-ground net primary productivity (ANPP), ANPP of functional groups (rhizomatous grasses, bunch grasses and forbs), and how the legacy effects were driven by plant species diversity, clonal traits and vegetative traits.3. We found that drought progressively reduced total ANPP over the 4-year period. The reductions in total ANPP in the first and third drought years were caused by the decrease in ANPP of bunch grasses only, while that of the second year was caused by declines in ANPP of bunch grasses and forbs, and the fourth year decline was linked to all three functional groups. The post-drought recovery of ANPP, which occurred despite the continued loss of plant species diversity, was mainly driven by rapid recovery of rhizomatous and bunch grasses, which compensated for the slow response by forbs. The rapid post-drought recovery of these grasses can be attributed to their relatively large, intact bud and shoot densities post-drought, as well as the recovery of plant height and specific leaf area. The rapid recovery of grasses possibly restricted the growth and distribution of forbs, resulting in reduced forb ANPP and, consequently, lower species diversity during the recovery period.4. Synthesis. These results highlight the potential for positive legacy effects of drought on ANPP as well as the important and complementary roles of plant reproductive and vegetative traits in mediating ecosystem recovery from drought in a C-3-dominated grassland.