Many biodiversity experiments have demonstrated that plant diversity can stabilize productivity in experimental grasslands. However, less is known about how diversity–stability relationships are mediated by grazing. Grazing is known for causing species losses, but its effects on plant functional groups (PFGs) composition and species asynchrony, which are closely correlated with ecosystem stability, remain unclear. We conducted a six‐year grazing experiment in a semi‐arid steppe, using seven levels of grazing intensity (0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep per hectare) and two grazing systems (i.e., a traditional, continuous grazing system during the growing period (TGS), and a mixed one rotating grazing and mowing annually (MGS)), to examine the effects of grazing system and grazing intensity on the abundance and composition of PFGs and diversity–stability relationships. Ecosystem stability was similar between mixed and continuous grazing treatments. However, within the two grazing systems, stability was maintained through different pathways, that is, along with grazing intensity, persistence biomass variations in MGS, and compensatory interactions of PFGs in their biomass variations in TGS. Ecosystem temporal stability was not decreased by species loss but rather remain unchanged by the strong compensatory effects between PFGs, or a higher grazing‐induced decrease in species asynchrony at higher diversity, and a higher grazing‐induced increase in the temporal variation of productivity in diverse communities. Ecosystem stability of aboveground net primary production was not related to species richness in both grazing systems. High grazing intensity weakened the temporal stabilizing effects of diversity in this semi‐arid grassland. Our results demonstrate that the productivity of dominant PFGs is more important than species richness for maximizing stability in this system. This study distinguishes grazing intensity and grazing system from diversity effects on the temporal stability, highlighting the need to better understand how grazing regulates ecosystem stability, plant diversity, and their synergic relationships.

Grasslands are widely used for production of livestock, which depend on the nutritive value of herbage species. However, there are still large uncertainties as to how grazing, precipitation and growing season interactively affect herbage nutritive value. Here, based on a grazing experiment with seven grazing intensities in an Inner Mongolian grassland since the year 2005, we analysed nutritive value of four dominant grass species from June to September in both a relatively wetter year (2008) and a drier year (2010). Herbage with high nutritive value is characterized by high concentration of crude protein, high concentration of cellulase digestible organic matter and low concentration of neutral detergent fibre. We found that (i) grazing significantly increased the nutritive value of Leymus chinensis, Agropyron michnoi and Cleistogenes squarrosa but had minor effects on the nutritive value of Stipa grandis. (ii) For all species, nutritive values were greater in the wetter year than in the drier year and were greatest in the early growing season (June) and lowest at the end of the growing season (September). Inter-annual and inter-seasonal variations in nutritive value were much greater for L. chinensis and A. michnoi than for C. squarrosa and S. grandis, suggesting higher water use efficiency for the latter two species. (iii) Grazing significantly decreased the drought resistance of three species, but not of S. grandis. (iv) Grazing significantly increased inter-month variation in nutritive value for L. chinensis and A. michnoi but had relatively minor or no effects on that of C. squarrosa and S. grandis. Therefore, grazing effects on species nutritive values showed strong inter-annual and seasonal patterns, and species-specific responses might be related to species traits (i.e. water use efficiency, digestibility). Our results have important implications for ecosystem management of arid and semi-arid grasslands under intense grazing and global climatic change.