Abstract:

Calcium (Ca) is an essential nutrient for plant growth and Ca concentrations in forage have important implications for ruminant diet and health. It remains an open question whether forage Ca concentration would be decreased by increasing nitrogen (N) deposition. We manipulated the increasing rates of N addition (2008–2015) in a semiarid grassland, northern China. Plant Ca concentrations for all species were examined in each plot under N treatment. The Ca concentrations at functional group and community levels were calculated based on the concentration of each species presented and their relative biomass in each plot. We found that community-level Ca concentration remained stable across a gradient of wide-ranged N addition rates, although Ca concentration at both species and functional group levels showed negative responses to N enrichment. Given that forbs had higher Ca concentration than grasses, the increasing relative biomass of forbs canceled out the negative responses of species-level and functional group-level Ca concentration. Our results further showed that community Ca pool showed a positive but saturating response to N addition, with a threshold at the rate of 10 g N m⁻² yr⁻¹. Our findings highlight the role of changes in plant relative biomass in controlling the responses of forage Ca concentration and stock to N enrichment.

Key words: calcium stock, community composition, ecological processes, global changes, nitrogen deposition, temperate steppe