Response To Grazing On Vegetation And Live-weight Gain In Alpine Steppe Around Qinghai Lake

In this study, five grazing gradient and one control were set up to conductyear-round continuous grazing trial, with Tibetan sheep as experimental animals inalpine steppe around Qinghai Lake. With combination of field investigation andlaboratory analysis, the primary productivity, secondary productivity, plantcommunity structure and species diversity and forage nutrients under differentgrazing intensities were studied to explore the relationship between grassland plants,livestock weight and grazing intensity. This study can provide basic data for makingout rational grazing management strategies of alpine steppe around Qinghai Lake,determining the appropriate stocking rates, the rational utilization of alpine grasslandaround Qinghai Lake. The main results obtained as follows:1. With the increasing of grazing intensity, the vegetation coverage decreased(P<0.05), dominance of good palatability forage (Stipa purpurea and Poa sp.)decreased, dominance of some forbs and grazing resistance forage (Kobresiapygmaea) increased. Community with Stipa purpurea and Poa sp. being the dominantpopulations may be in degradation direction on community with Kobresia pygmaeaand Thermopsis lanceolata being the dominant populations.2. With the extension of grazing time, community species richness index anddiversity index increased as grazing intensity increased. Evenness index was high inmoderate grazing. Richness index and diversity index were the highest in heavygrazing, which mainly related to the increasing forbs in the community.3. With the increasing of grazing intensity, the proportion of gramineous foragedecreased and the proportion of forbs increased, community above-ground biomassdecreased significantly(P<0.05). It was a significant linear negative correlationbetween average above-ground standing crop in growing season and grazing intensity(P<0.05). Below-ground biomass is higher in moderate to heavy grazing and had aquadratic curve function relationship with grazing intensity. The plant roots tended toassemble to the surface result from grazing and75%to88%below-ground biomassdistributed in0to10cm soil layer. Root-shoot ratio had a increasing trend with theincreasing of grazing intensity, which was an adaptive strategy of plants to grazing disturbance.4. With grazing time increasing, crude protein content and phosphorus content ofherbage showed the change of the low-high-low and crude fat, crude fiber andcalcium content had a increasing trend as growth time increased. Moreover, the crudeprotein, crude fat and calcium content of herbage under different grazing intensityincreased as grazing intensity increased. The herbage crude ash content had a notobvious variation as the grazing time and grazing intensity changed. However, thecrude ash content of herbage in no grazing was significantly higher than the grazinggroup. Grazing not only slow down the variation that the herbage crude proteincontent decreased as growth time increased, but also slow down the speed of herbagefibrosis.5. Under different grazing intensity, sheep live-weight showed a rising trendwith grazing time increasing. In the early grazing, the difference of sheep live-weightunder different grazing intensity was not obvious. With the grazing time increasing,the difference of sheep live-weight under different grazing intensity was more andmore obvious, which showed sheep live-weight decreased as stocking rate increased.Sheep live-weight gain had a faster speed under different grazing intensity in June toOctober, to the maximum weight in October. The change of sheep live-weight wasnot obvious from October to December. After December, the live-weight decreasedlinearly and had the minimum weight at the end of April to early may of the next year.6. Live-weight gain per sheep decreased with grazing intensity increasing, andhad a significant negative linear correlation with stocking rate. Live-weight gain perhectare increased as the grazing intensity increased under different grazing intensity.In the first cycle of grazing, live-weight gain per hectare had a linear relation withstocking rate and in the second grazing cycle live-weight gain per hectare had aquadratic function relation with stocking rate. The potential of live-weight gain in thefirst grazing cycle was greater than in the second cycle.