Warming effects on plant regrowth after clipping are modified by repeated clipping in Mongolian pasture species

Global warming may pose a threat to the productivity of grazed grasslands. In this study, we investigated changes in the warming response of aboveground regrowth with the repetition of simulated grazing in two Mongolian pasture species, Agropyron cristatum and Stipa krylovii. Plants were grown under warming or non-warming conditions and subjected to repeated clipping of aboveground parts three times at 4-week intervals. Aboveground parts collected at each clipping and whole plants harvested at the end of the experiment were dried and weighed. Specific leaf area (SLA) and the content of nitrogen (N) and crude fiber (CF) in leaves were measured to evaluate leaf morphology and pasture nutritional value. In both species, warming had little effect on regrowth when clipping was repeated one or two times. In A. cristatum, however, warming significantly diminished regrowth when clipping was repeated three times. Belowground biomass decreased with clipping–regrowth cycles only in A. cristatum, and the decline was enhanced by warming, implying that the depletion of belowground reserves contributed to the reduction of regrowth in this species. SLA and the N and CF contents were similar in the warming and non-warming treatments, indicating that warming had little effect on leaf morphology and pasture nutritive value in these Mongolian pasture species. Our results suggest that warming would likely have little effect on regrowth performance of grassland plants under lightly grazed conditions, but warming can decrease regrowth when grazing frequency is high, with the degree of decrease being species dependent.