Seasonality regulates the effects of resource addition on plant diversity and ecosystem functioning in semi-arid grassland

Aims Seasonal variations in species richness, aboveground net primary productivity (ANPP) and stability under resource enrichment are frequently ignored. This study explores how the impacts of resource enrichment on species richness, ANPP and stability vary among seasons in semi-arid grasslands. Methods We conducted a 3-year experiment in an Inner Mongolia grassland to determine the effects of resource input (water [W], nitrogen [N]) on species richness, community ANPP and stability using seasonal sampling during the growing season (2013–2015). Structural equation modeling (SEM) was used to examine the relative importance of resource input on community stability via mechanistic pathways in each month and the whole growing season. Important Findings Resource inputs did not affect community ANPP in May and June, while N and/or NW enhanced ANPP in July and August. Resource inputs generally did not affect species richness, asynchrony or community stability in most of the time. Positive responses of perennial bunchgrasses (PB) to N and/or NW treatments contributed to the increased community ANPP in July and August. Species asynchrony may be the major mechanism contributing to community stability in May and June and the entire growing season, and PB stability is potentially the primary factor controlling community stability in July and August under resource enrichment. Our results indicate that season and resource availability could interact to regulate species richness, community ANPP and stability in semi-arid grasslands. These findings have important implications for management practices in semi-arid grasslands in order to mitigate the impact of land use and global change.