| Litter, as an important component of grassland ecosystem, plays an important role in water conservation, soil and water conservation, as well as in the material cycle of grassland ecosystem and even in the whole earth cycle. Grazing by foraging and trampling not only affect the litter accumulation and biomass, but also has great influence on its decomposition. Trampling was one of the three main factors influencing the grassland, and accompanied by the whole process of grazing. Therefore, it is very necessary to research trampling as a subject. In depth understanding of the response of the main plant litter decomposition characteristics in the alpine grassland, and provides a theoretical basis for the management of the ecological system of the Qinghai Tibet Plateau, so the following three aspects were studied on litters: 1) three kinds of litters(Elymus nutans、Kobresia humilis、Polygonum viviparum) loss rate and change of stoichiometry under the condition of the rotational grazing, 2) the change of existing mixed litter biomass and stoichiometry in the traditional cold season pasture, and 3) the three kinds of litters loss rate and change of stoichiometry under the trampling simulation. The results of the studies are listed as follows:1. With the increasing of grazing intensity, the loss rate of litter was increased, the litter carbon(C), nitrogen(N) and phosphorus(P) content was decreased. Under the same grazing intensity, the loss rate of litter in the plot of grazing yak was greater than that of Tibetan sheep, the litter C, N content was lower than that of Tibetan sheep. Under the same grazing intensity, E. nutans litter loss rate was significantly less than that of K.humilis and P. viviparum. C content of E. nutans litter was significantly greater than that of K. humilis and P. viviparum, but C content of E. nutans litter change was less than that of K. humilis and P. viviparum. With the increase of grazing processing time, the litter P content basically showed increasing trend. There were inhibitory effects on the accumulation of phosphorus in litter under both grazing treatments. This inhibitory effect of grazing yak was more inhibited than that of Tibetan sheep.2. In the cold-season pasture, the existing amount of mixed litter was significantly reduced with the increase of grazing time. However, there was a trend of increase in the amount of mixed litter in the period of rest grazing. Under different grazing intensity, the biomass of mixed litters was as follow: light grazing(LG) > moderate grazing(MG) > heavy grazing(HG). The C content of the existing litter gradually decreased in the grazing season, with the increase of grazing time. The C content of the litter in the same period was as follows: LG> MG > HG. During the rest period, the C content of litter was not significantly changed with the time went by. In the same period, the C content of litter was significantly under MG higher than that of LG and HG. The N content of litter in the grazing period showed a decreasing trend at same time, with the increase of grazing time. The N content of litter in the early stage of rest grazing showed a decreasing trend with the increase of grazing intensity. The P content of the existing litter under light grazing showed fluctuating increase trend, but the P content of litter in the rest period was lower than that in the period of grazing.3. The loss rate of litters(P. viviparum, K. humilis and E. nutans.) were increased with the simulated trample intensity increasing. The impact of yak trample on litter loss was bigger than that of Tibetan sheep. The litter loss rate was followed under the same intensity: P. viviparum> K. humilis > E. nutans. With the increase of the trample intensity, P.viviparum litter carbon content was decreased under simulated trampling(P<0.05). With increasing treatment time, the content of N and P in the 3 kinds of litter increased gradually, and the K content decreased, the N content of P.viviparum and K. humilis litter were decreased gradually. |
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