Drought frequency has significantly increased worldwide as a result of global change, resulting in great damage to grassland ecosystem functioning. Drought events affect not only the current composition and structure of grassland plant communities, but also their future structure and function and their responses to environmental changes. Previous studies have focused on examining plant community resistance to drought, while the research on structural and functional resilience of plant communities after extreme drought is far from enough.

In view of this, Dr. LUO Wentao, associate researcher of the Eco-stoichiometry research group of the Institute of Applied Ecology, Chinese Academy of Sciences, led a study examining grassland natural restoration following two consecutive years of extreme drought manipulation, and explored the carry-over effects of the extreme drought event on plant community structure and function.

The researchers found that within two years after the cessation of extreme drought treatment, plant productivity of the drought-treated communities could be largely restored, or even significantly higher than that of control communities, suggesting that extreme drought can result in a positive carry-over effects, which in turn can improve the sustainability and stability of grasslands. This finding challenges the conventional judgment that "drought has negative carry-over effects on grassland productivity."

The researchers clarified that the positive carry-over effect occurred due to the rapid recovery of grasses and their competitive exclusion effect on forbs, as well as an obvious change in plant community functional composition (the ratio of grasses to forbs). 

"When extreme drought events recurred, the plant community composition could be altered even more significantly compared to the impact of a single extreme drought," said the researchers. And they added that the drought induced changes in plant community-level traits and functions may weaken the stability of the plant community in response to the next extreme drought. 

Exploring the variation and maintenance mechanisms of grassland ecosystem function in response to drought is one of the 'hotspots' in global change ecology. The study indicates that the impact of extreme drought on grassland ecosystems will continue even after the drought ends. The carry-over effects of extreme drought and their driving mechanisms that unraveled by the study are crucial for understanding and predicting the impact of global climate change on grassland ecosystems.

This study, funded by the National Key R&D Program and the National Natural Science Foundation of China and the Major Program of IAE, CAS, has been published in Ecology entitled "Responses of a semiarid grassland to recurrent drought are linked to community functional composition."