Later-melting rather than thickening of snowpack enhance the productivity and alter the community composition of temperate grassland

Snowpack is closely related to vegetation green -up in water -limited ecosystems, and has effects on growingseason ecosystem processes. However, we know little about how changes in snowpack depth and melting timing affect primary productivity and plant community structure during the growing season. Here, we conducted a four-year snow manipulation experiment exploring how snow addition, snowmelt delay and their combination affect aboveground net primary productivity (ANPP), species diversity, community composition and plant reproductive phenology in seasonally snow-covered temperate grassland in northern China. Snow addition alone increased soil moisture and nutrient availability during early spring, while did not change plant community structure and ANPP. Instead, snowmelt delay alone postponed plant reproductive phenology, and increased ANPP, decreased species diversity and altered species composition. Grasses are more sensitive to changes in snowmelt timing than forbs, and early -flowering forbs showed a higher sensitivity compared to lateflowering forbs. The effect of snowmelt delay on ANPP and species diversity was offset by snow addition, probably because the added snow unnecessarily lengthens the snow -covering duration. The disparate effects of changes in snowpack depth and snowmelt timing necessitate their discrimination for more mechanistic understanding on the effects of snowpack changes on ecosystems. Our study suggests that it is essential to incorporate non -growing -season climate change events (in particular, snowfall and snowpack changes) to comprehensively disclose the effects of climate change on community structure and ecosystem functions.