Effects of grazing on litter decomposition in two alpine meadow on the eastern Qinghai-Tibet Plateau

Abstract

Litter decomposition is an important component of nutrient cycling and carbon decomposition in grassland ecosystems, and livestock grazing has been a major human intervention to these process. The effects of grazing on litter decomposition vary with climate environment conditions and grassland vegetation types. Alpine mesophytic meadow and alpine semi-hydric marsh meadow are the two rangeland ecosystems commonly seen on the eastern Qinghai-Tibet Plateau, which differentiate themselves by not only the physic/ bio environments but also the plant species composition and therefore the litter qualities. In order to understand grazing effects on the litter decomposition of these two meadows, grazed and fenced plots were set respectively on the both meadows. The rates of decomposition and nutrient release were measured for the three littler samples (mesophytic meadow mixed litter, Deschampsia caespitos litter, and Potentilla anserine litter) in the alpine mesophytic meadow plots, and three litter samples (semi-hydric marsh mixed litter, Carex muliensis litter, Kobresia tibetica litter) in the semi-hyddric marsh meadow plots. The four species generally also represented the dominant species showing respectively in the reverse succession series driven by grazing and climate warming. It was found that there were significant differences in litter decompositions for the dominant species. In alpine mesophytic meadow, Potentilla anserine decomposed faster than Deschampsia caespitos, while in alpine semi-hydric meadowKobresia tibetica decomposed more quickly. Grazing accelerated the litter decomposition in general, but the responses varied with the species. On the other hand, Deschamp siacaespitos and Carex muliensis have lower decomposition rates in the grazed plots. Grazing has little effect on organic carbon decomposition and the release of C, but positively affected on the release of N and P from the litters. The patterns of litter decomposition and nutrient release of the dominant species suggested that there might exist a positive feedback effect in the alpine marsh meadow degradation due to the accelerating decomposition rate and C release along the reverse succession series. In addition, Potentilla anserine, a typical dominant species of in degraded meadow, was found to have higher litter quality and faster decomposition rate than the other species, reflecting that in the mesophytic community, the plant adopted 'evasion strategy' rather than 'resistance strategy'in response to heavy grazing.