| The alpine meadow of the Qinghai-Tibet plateau(QTP), the highest, largest and the most unique type of plateau in the world, is known as the roof of the world. The alpine meadow of QTP has beening seriously degraded because of its unique geographical location and harsh natural environmental conditions, combined with recent global climate change, human occupation and animal grazing, and rats and insect pests. Reasonable grazing management is one of the main approaches to restore the degraded grassland ecosystem, and has important implications for the healthy development and sustainable use of grassland. However, there is litter information about the effects of different grazing regime on vegetation structure and composition, soil characters and carbon(C) and nitrogen(N) storage in alpine meadow of the QTP. Therefore, a short term field experiment was conducted to quantify the impact of four different grazing management regimes(fencing: NG, rest-grazing in growing seasons(RG), traditional grazing(TG) and continued grazing(CG)) on an alpine meadow ecosystem of the QTP in northern China and investigated vegetationcommunity alterations, soil physicochemical properties and C and N storage regarding grazing regime. The purposes of this research were to compare the changes in vegetation structure and composition, soil properties and C and N storage under different grazing regimes meadow to evaluate the effects of grazing regime on the alpine meadow ecosystem of the QTP. According to the results of this research, we could recommend an optimal and sustainable grazing pattern that not only avoid over grazing and prevents the grassland for further degradation, but also promote the efficient use of grassland resources, and help to restore forage productivity and maintain the grassland ecosystem. The results are as follows:1. The height of gramineous, leguminous, sedge and forbs plant functional groups increased, aboveground and belowground biomass of gramineous plant, and the dominant gramineous plant important values of Elymus nutans were all increased with grazing ceasing of NG and RG, especially obvious with NG. However, the important values and the ratio in aboveground and underground community biomass of forbs were all decreased. The Shannon-Wiener index(H), Pielou evenness index(J), richness index(S) and total density of plant community are in an order of CG<NG<TG<RG.2. The bulk densities and soil compaction at NG, RG and TG were lower than those at the CG. While the soil water content at NG, RG and TG were higher than that at CG site. The soil organic matter in 0~30 cm soil layer was significantly higher in NG than that in RG, TG and CG, and in 0~20 cm soil layer was significantly higher in RG and TG than that in and CG. NG, RG and TG significantly improved 0~30 cm soil layer total nitrogen content and 20~30 cm soil layer available nitrogen content, but reduced the 0~10 cm soil layer available nitrogen content in the alpine meadow. The total soil phosphorus and available phosphorus content of alpine meadow in 0~30 cm soil layer was significantly higher in NG, RG and TG than those in CG. Different grazing model management had no significant effect on soil total potassium content, but on the whole, NG, RG and TG is higher than CG.3. The Soil respiration differed from month to month under the different grazing patterns, first increasing and then decreasing. In all of the treatments except for CG, the highest soil respiration rates were in August, and were significantly higher than those in the other months. There was no significant difference in soil respiration between August and September in the CG treatment, but the rates in both months were significantly higher than those in other months. In the growing season, soil respiration was significantly higher in the NG, RG and TG plots than in the CG plot, and there was no significant difference in soil respiration between the NG and RG plots. There was a significant positive correlation between soil respiration and soil temperature under all of the rest grazing patterns, but not under CG. Based on the Q10 values, the plots were ranked as follows: NG>RG>TG>CG. There was a threshold at which the effects of soil water content on soil respiration changed; that is, the two were positively correlated at soil water contents of 30% or lower, and negatively correlated at soil water contents of >30%. Soil respiration was significantly correlated with aboveground and belowground biomass.4. The soil organic carbon and nitrogen in 0~80 cm soil layer, roots, aboveground tissue and litters was significantly higher in NG, RG and TG than those in CG. In alpine meadow ecosystem, the proportion of soil organic carbon is the largest(88.8%-98.2%), roots the next(1.6%-8.7%), vegetation again(0.17%-1.43%), and litters the smallest(0.022%-0.97%); the proportion of soil nitrogen is the largest(97.3%-99.6%), roots the next(0.32%-2.07%), vegetation again(0.05%-0.44%), and lit-ters the smallest(0.003%-0.16%). There were obvious vertical distributions in the soil organic carbon and nitrogen storage under different grazing management regime, and the different grazing management mode mainly affected 0~40 cm soil layer soil organic carbon storage and nitrogen storage, but had no significant effect on the deeper. Soil organic carbon and nitrogen storage are mainly distributed in the 0~40 cm soil layer, and grazing has made the trend of organic carbon and nitrogen to deeper. NG, RG and TG significantly increased the alpine meadow ecosystem total organic carbon and nitrogen storage, but the CG significantly reduces the total organic carbon and nitrogen storage, and turn into a loss of carbon and nitrogen.Our results demonstrated that fencing is superior grazing regime on an alpine meadow ecosystem of the QTP, whereas in the long term, management interventions should be taken to promote the sustainable development of grasslands. However, considering the use and update of grassland resources and the economic income stability of the herdsmen, the rest-grazing at growing seasons could not only help to restore forage productivity and maintain the grassland ecosystem, but also promote the efficient use of grassland resources, therefore, rest-grazing at growing seasonsis the optimum management strategy for the alpine meadow grassland of the QTP. |
PDF Full Text Request