Background Livestock grazing and nitrogen (N) deposition potentially affect carbon (C), N and phosphorus (P) cycles in grassland ecosystems. Despite the single effects of livestock grazing and N deposition change on C, N and P storage are well understood, how the interaction of both effects on grassland remains unclear.
Methods Field trials with four stocking rate (grazed for 17 years at 0, 2.7, 5.3, and 8.7 sheep ha–1) and N deposition (from 2013 at 0, 5, 10, and 20 g N m–2 yr–1) were conducted to measure aboveground biomass, root, litter and soil C, N and P pools in typical steppe of the Loess Plateau.
Results/Conclusions
Results Our results showed that, in general, grazing significantly decreased C pools in aboveground biomass, root and litter, and the lowest at the stocking rate of 2.7 or 5.3 sheep/ha by 82.7%, 75.9.1% and 97.4%, respectively, N pools by 827%, 75.6%, and 97.7%, respectively, and P pools by 93.9%, 50.2 and 48.8%, respectively. However, grazing decreased soil C and N pools when the stocking rate was lower than 5.3 sheep/ha, and then increased. By contrast, grazing increased soil P pool. N deposition did not significantly change C, N and P pools in aboveground biomass and litter, while significantly promoted belowground C, N and P pools at the gradient of 20 g N m–2 yr–1 by 18%, 20.9% and 21.6%. and increased soil C and N pools at the gradient of 5 g N m–2 yr–1 by 2.4% and 8.2%. The interactions of grazing and N deposition significantly affected ecosystem P pools and soil C pool, and grazing enhanced the responses of P pools in grassland and soil C pool to nitrogen deposition at some gradient.
Conclusion Our findings highlighted the grazing compared with N deposition contributed more to the variations of the ecosystem C, N and P pools in grassland.