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Nitrogen addition stimulated compensatory growth responses to clipping defoliation in a Northern Tibetan alpine meadow

Zong, Ning, Shi, Peili
Grassland science 2019 v.65 no.1 pp. 60-68
Cyperaceae, alpine meadows, animal feeding, anthropogenic activities, community structure, compensatory growth, defoliation, ecosystems, forage production, forbs, grasses, grazing, livestock husbandry, nitrogen, nitrogen content, phytomass, regression analysis, soil
Grazing and clipping defoliation are the most important human disturbances in natural grasslands. Compensatory growth is a common response to clipping defoliation, which is of great significance for forage production and livestock husbandry development. However, how clipping intensity affects plant compensatory growth and how nitrogen (N) addition regulates this response in alpine ecosystems are still unclear. A manipulative experiment including two clipping intensities (light and heavy) crossed with N addition was conducted in an alpine meadow ecosystem to examine the effects of how N addition regulated plant compensatory growth induced by clipping defoliation. Selective clipping was used to simulate animal feeding, that is, only grasses and sedges were clipped. Under the N addition treatment, the relative growth rate of grasses and total biomass after clipping were significantly higher than those under the no N addition treatment. The total community biomass showed over‐compensatory growth in light clipping under N addition treatment, while it showed equal‐compensatory growth under the other treatments. The over‐compensatory growth in light clipping under the N addition treatments mainly resulted from the stimulated growth of grasses. Regression analysis showed that the relative growth rate and biomass of grasses were positively correlated with soil inorganic N content, but increasing N availability was not conducive to the growth of sedges and other forbs. Divergent responses of different plant functional groups to clipping and N addition would lead to changes in community structure and functioning. Both community biomass and compensatory growth tended to increase first and then reach a stable state with the increase in soil N availability. Our results show that although light clipping could largely stimulate forage production under N addition, excessive clipping cannot lead to a continuous increase in compensatory growth of plant biomass, even under N addition conditions, in this semiarid alpine meadow ecosystem.