Extreme drought alters plant community structure by changing dominant species growth in desert grassland

Questions: Interannual precipitation changes, both in amount and frequency, are expected to increase due to climate change, and these changes could dramatically affect the structure and function of ecosystems. However, how plant life-forms and dominant species regulate the plant community structure after precipitation changes remains unclear.Location: Gaolan Experiment Station for Ecology and Agriculture Research of the Northwest Eco-Environment and Resources Research Institute of the Chinese Academy of Sciences, located in the desert grassland of the western Loess Plateau, China.Methods: To investigate the effect of precipitation changes on the growth of communities, life forms, and species, we used rain shelters and irrigation to create a variety of precipitation gradients (i.e., -40%, -20%, 0% [= CK, i.e., control treatment], +20%, +40% of ambient precipitation) in desert grasslands from 2014 to 2015.Results: The plant community density, coverage, and height were significantly decreased in the -40% treatment compared to CK. In contrast, species richness, Shannon-Wiener index, and Pielous' evenness did not respond significantly to the precipitation treatment. In addition, at the level of life-forms, the density of perennial herbaceous plants was significantly increased by the +40% treatment in 2015, while the richness and density of annual herb were significantly inhibited by extreme drought. The effect on the shrub growth index of increasing and decreasing precipitation compared to the CK was insignificant. Furthermore, at the level of species, the growth of dominant species is obviously suppressed by the -40% and +40% treatment in 2015. However, the positive effect of the +40% treatment on the growth of rare species reached significant levels in 2015. Also, the change in precipitation did not have a significant effect on the growth of companion species. Dominant species primarily drove the response of community-level plant growth to precipitation changes over the three-year study period.Conclusion: The response of plant community composition to changes in precipitation in desert grassland is largely regulated by changes in the composition of the dominant species. This finding could also provide a better prediction of the effects of extreme drought on desert grassland plant communities in the scenarios of future global climate change.