模拟践踏和降水对高寒草甸土壤养分和酶活性的影响

为明晰牦牛和藏羊践踏对高寒草甸的分异影响,通过2年模拟践踏和降水双因子控制试验,研究了践踏和降水对高寒草甸土壤养分和酶活性的影响。研究结果表明,践踏处理提高了0—20 cm土层土壤速效氮和速效钾含量,降低了0—20 cm全磷、脲酶和0—10 cm速效磷、碱性磷酸酶和有机质含量,且适度践踏促进了全氮的矿化。随降水强度的增加,0—30 cm土层土壤全氮和0—20 cm全磷和脲酶活性呈单峰曲线的变化态势,在平水下达到峰值;降水显著降低了0—30 cm土层土壤速效氮、磷、钾和0—10 cm土层土壤全钾含量,对土壤有机质含量无显著影响(P0.05)。同一放牧强度下,藏羊践踏区的土壤养分和酶活性优于牦牛践踏区,但差异不显著(P0.05)。综合可得,家畜的践踏作用促进了土壤氮和钾的矿化,抑制了磷的累积且加速了表层土壤有机质的耗竭,降低了土壤脲酶和碱性磷酸酶活性;适度降水提高了土壤全氮、全磷含量及酶活性,降水过多则相反。适度的家畜践踏与降水相耦合下草地土壤的养分循环和酶活性要优于重度践踏和不践踏小区。在对草地的适度放牧利用前提下,应注重土壤含水量和放牧畜种对草地的影响。草地干旱或土壤含水量过高时,应适当减少放牧畜种中牦牛比例增加藏羊比例,以期使草地得到健康可持续发展。

Effects of simulated trampling and rainfall on soil nutrients and enzyme activity in an alpine meadow

The aim of this study was to clarify the effects of yak and Tibetan sheep trampling on the grassland in Qinghai-Tibetan Plateau. The effects of simulated trampling and rainfall on soil nutrients and enzyme activity in an alpine meadow were studied through two years of two-factor control experiments. The results showed that simulated trampling increased soil available nitrogen and available potassium but decreased soil total phosphorus and urease in the 0-20 cm soil layer, and decreased available phosphorus, alkaline phosphatase activity, and organic matter content in the 0-10 cm soil layer. Moderate trampling promoted the mineralization of soil total nitrogen. The soil nitrogen content in the 0-30 cm layer and total phosphorus content and urease activity in the 0-20 cm layer each showed a trend of a single peak curve with increased rainfall, reaching its peak at the average level of rainfall. Precipitation significantly reduced available nitrogen, available phosphorus, and available potassium in the 0-30 cm soil layer and total potassium in the 0-10 cm soil layer, but had no significant effect on soil organic matter content (P > 0.05). Under the same grazing intensity, the soil nutrients and enzyme activity of soil with Tibetan sheep were better than those with yak, but the difference was not significant (P > 0.05). Overall, livestock trampling promoted the mineralization of soil nitrogen and potassium, inhibited the accumulation of phosphorus, and accelerated the depletion of soil organic matter in the topsoil, while reducing soil urease and alkaline phosphatase activities. Moderate rainfall increased total nitrogen and total phosphorus contents and enzyme activity, while excessive rainfall had the opposite effect. Soil nutrient cycling and enzyme activity under the coupling of moderate trampling and precipitation were better than those of severe trampling and no trampling. As part of appropriate grazing and utilization of grassland, the influences of soil moisture and livestock species should be taken seriously. When grassland is under drought or soil water content is too high, the proportion of yak in grazing livestock should be reduced to increase the proportion of Tibetan sheep, so as to make the grassland achieve healthy and sustainable development.