Overcompensation of ecosystem productivity following sustained extreme drought in a semiarid grassland

Drought events are projected to be more extreme and frequent in the future
and have profound influences on the structure and functions of terrestrial
ecosystems. Thus, better understanding the mechanisms of recovery is
critical for predicting the future dynamics of terrestrial ecosystems. We
performed a seven-year field precipitation experiment to examine recovery
of a grassland ecosystem from different magnitudes of sustained drought,
from slight to extreme. The ecosystem was exposed to precipitation
treatments in the first three years (2010-2012) and recovered during the
last four years (2013-2016) without precipitation treatments. Overall,
large reductions of aboveground net primary productivity (ANPP, -43.3%)
and perennial forb biomass (-83.1%) were observed in the 3rd year (2012)
of extreme drought only. Nevertheless, ANPP fully recovered within one
year after the drought treatments were terminated, and the rapid recovery
was mainly due to increased soil total nitrogen and root biomass
allocation after drought. Surprisingly, large increases of ANPP under the
extreme drought treatment occurred during the recovery periods from
2013-2015 (+74.1, +88.5, and +119.8 g m-2 yr-1) compared to the control.
The overcompensation offset the extreme drought-induced reduction of ANPP
in the treatment years and was primarily ascribed to the enhanced biomass
of perennial grasses. Higher resistance to drought and fast resource
acquisition strategy might drive the rapid recovery and expansion of
perennial grasses. Our findings revealed the rapid recovery of grasslands
and the critical role of community overcompensation in maintaining
grassland ecosystem function and stability under future climate change
scenarios.