Responses of a semiarid grassland to recurrent drought are linked to community functional composition

   Recurrent droughts are an inevitable consequence of climate change, yet how grasslands respond to such events is unclear. We conducted a six-year rainfall manipulation experiment in a semiarid grassland that consisted of an initial two-year drought (2015-2016), followed by a recovery period (2017-2018), and finally a second two-year drought (2019-2020). In each year, we estimated aboveground net primary productivity (ANPP), species richness, community-weighted mean (CWM) plant traits, and several indices of functional diversity. The initial drought led to reduced ANPP, which was primarily driven by limited growth of forbs in the first year and grasses in the second year. Total ANPP completely recovered as the rapid recovery of grass productivity compensated for the slow recovery of forb productivity. The subsequent drought led to a greater reduction in total ANPP than the initial drought due to the greater decline of both grass and forb productivity. The structural equation models revealed that soil moisture influenced ANPP responses directly during the initial drought, and indirectly during the subsequent drought by lowering functional diversity which resulted in reduced total ANPP. Additionally, ANPP was positively influenced by CWM plant height and leaf nitrogen during the recovery period and recurrent drought, respectively. Overall, the greater impact of the second drought on ecosystem function than initial drought as well as the differential underlying mechanism underscores the need for understanding how increased drought frequency may alter semiarid grassland functioning. </p

Inter- and intraspecific trait variability differentially affect community-weighted trait responses to and recovery from long-term drought

   1. Plant traits are useful proxies of plant strategies and can influence community and ecosystem responses to climate extremes, such as severe drought. Few studies, however, have investigated both the immediate and lagged effects of drought on community-weighted mean (CWM) plant traits, with even less research on the relative roles of inter- vs. intraspecific trait variability in such responses.  2. We experimentally reduced growing season precipitation by 66% in two cold-semiarid grassland sites in northern China for four consecutive years to explore the drought resistance of CWM traits as well as their recovery two years following the drought. Additionally, we isolated the effects of both inter- and intraspecific trait variability on shifts in CWM traits.  3. At both sites, we observed significant effects of drought on inter- and intraspecific trait variability which, in some cases, led to significant changes in CWM traits. For example, drought led to reduced CWM plant height and leaf phosphorous content, but increased leaf carbon content at both sites, with responses primarily due to intraspecific trait shifts. Surprisingly, these CWM traits recovered completely two years after the extreme drought. Intraspecific trait variability influenced CWM traits via both positive and negative covariation with interspecific trait variability during drought and recovery phases.  4. These findings highlight the important role of inter- and intraspecific trait variability in driving the response and recovery of CWM traits following extreme, prolonged drought.</p