Abstract: Grazing is significant factor impacting the ecological processes of grassland ecosystems.This study was conducted to investigate the effects of natural grazing intensity on plant community and soil nutrients in alpine meadow.Using comparative experiments,research was initiated under different grazing intensities to provide a theoretical basis for defining the reasonable stocking rate of alpine meadow.Our results showed that: Both above-ground biomass and species richness of plant community were the highest in fencing than that in light and moderate grazing,and the least in heavy grazing treatment;Shannon-Wiener diversity index was not significantly different among fencing,light and moderate grazing;the above-ground biomass and cover of palatable herbages(grasses and sedges) was reduced with grazing intensity increasing,while the forbs in heavy grazing treatment had higher above-ground biomass than that in fencing,light and moderate grazing;over three growing stages,soil moisture decreased with grazing intensity enhancing in May,but increased in July and September;the soil bulk density in moderate grazing was significantly lower than that in other three grazing treatment(P<0.05);the pH value was the highest(pH 7.31) in heavy grazing and was not significantly different among fencing,light and moderate grazing treatment;soil organic carbon was reduced with increasing grazing intensity in plant growing stages;soil total nitrogen was not significant different among light,moderate and heavy grazing treatment.However,soil ammonium-N and nitrate-N increased along the increasing of grazing intensities over the whole plant growing stages;soil available phosphorus shared the same trend as total phosphorus that they had the highest value under moderate grazing.Our result suggested that the moderate grazing was effective way to protect biodiversity and improve grassland productivity,while fencing is beneficial for recovering of the degraded alpine meadow.

Key words: Alpine meadow, Grazing intensity, Function class group, Soil physical and chemical property, Plant diversity

摘要： 放牧作为最主要的生物干扰因子之一,影响着草地生态系统植被和土壤的生态进程。在自然放牧条件下,通过不同放牧强度的比较试验,对高寒草甸土壤营养成分及地上群落特征进行分析,为制定合理的放牧强度提供理论依据。结果表明:随着放牧强度加大,地上总生物量、物种丰富度在封育样地最高,在重牧样地最低,而封育、轻牧、中牧样地香浓-威纳多样性指数并没有显著的差异;禾草和莎草的地上生物量和总盖度在中牧条件下最高。与轻牧、中牧和封育样地相比,重牧样地的杂草有较高的地上生物量和总盖度;5月份土壤含水量随放牧强度增加而减少,7月份、9月份则相反;封育、轻牧、重牧样地的土壤容重显著低于中牧样地(P<0.05);在整个生长季节,重牧样地的pH值明显高于其他3个处理,而封育?轻牧?中牧3个样地pH值没有显著差异;在整个生长季节,封育、轻牧、中牧、重牧4个样地土壤有机碳含量随着放牧强度的增加而趋于下降,其中封育、轻牧、中牧3样地土壤有机碳含量都显著高于重牧样地(P<0.05);土壤的全氮含量在各放牧样地里并没有显著变化,而土壤氨态氮、硝态氮则在植物整个生长季节随着放牧强度的加大而增加;在整个生长季节里全磷含量最大值都出现在中牧样地里,速效磷含量表现出了和全磷一致的结果。因此,适度放牧是保护生物多样性,维持土壤养分以及提高草地生产力的有效途径;当高寒草甸由于退化导致生物量锐减,生物多样性丧失等严重后果时,围栏可以作为有效的恢复手段。

关键词: 高寒草甸, 放牧强度, 功能类群, 土壤理化性质, 植物多样性