模拟践踏和降水对高寒草甸土壤物理特性和微生物数量的影响

Effect of simulated trampling and rainfall on soil physical properties and microorganism abundance in an alpine meadow

为探讨牦牛和藏羊践踏对高寒草甸的影响分异,于甘肃天祝高寒草甸布设试验,研究了模拟践踏和降水对高寒草甸土壤物理特性和微生物数量的影响。研究结果表明,随着践踏强度和降水量的增大,0~10cm土层土壤的紧实度和容重也随之增大,而土壤饱和导水率呈递减趋势。0~10cm土层土壤呼吸速率随践踏强度的增大而降低,牦牛和藏羊重度践踏下的土壤呼吸速率较对照分别降低了37%和45%,而土壤呼吸速率随降水量的增加而显著增大(P<0.05)。随着践踏强度的增大,土壤表层的细菌菌落数呈现先增多后减少的趋势,而土壤中真菌和放线菌的菌落数均逐渐减少;三大类土壤微生物随降水量的增大均呈递增趋势;且随着土层的加深各微生物数量均呈递减趋势。10cm以下土层土壤的物理性质受家畜践踏的影响不显著(P>0.05)。同一降水量下牦牛践踏对土壤的压实效应高于藏羊;藏羊践踏后土壤容重和紧实度较对照分别增加了20%和39%以上,牦牛践踏后的土壤容重和紧实度较对照增幅达23%和44%以上;且牦牛践踏下的土壤呼吸速率、饱和导水率、三大类微生物数量均小于同践踏强度下的藏羊处理。总体而言,随着家畜践踏强度和土壤含水量的增大,土壤物理性质和微生物数量受其影响越大;家畜的践踏对土壤物理特性的影响主要作用于0~10cm土层,且牦牛对土壤的压实效应和对微生物分布的抑制作用均大于藏羊。

The aim of this study was to investigate the effects of yak and Tibetan sheep trampling and rainfall on the soil characteristics in an alpine meadow.In a field experiment conducted in an alpine meadow in Tianzhu,Gansu Province,simulated trampling and rainfall treatments were applied and the soil physical properties and microbial population were analyzed.The results showed that the soil compaction and bulk density increased at 0-10 cm soil depth with increasing trampling intensity and precipitation,while the saturated hydraulic conductivity decreased.The soil respiration rate decreased with increasing trampling intensity.The soil respiration rate was decreased by 37% and 45% under heavy trampling intensity by yaks and Tibetan sheep,respectively,compared with that in the control.The soil respiration rate significantly increased with increasing precipitation（P0.05）.As the trampling intensity increased,the bacterial abundance first increased and then decreased,while the abundance of fungi and actinomycetes gradually decreased.The abundance of all three types of microorganisms increased with increasing precipitation,and the number of microorganisms decreased in deeper soil layers.Below the 0-10 cm soil layer,there was no significant difference in soil physical properties between the two trampling treatments（P0.05）.Under the same precipitation conditions,trampling by yaks had a greater compaction effect on soil than did trampling by Tibetan sheep.Soil compaction and bulk density were increased by 20% and 39%,respectively,by Tibetan sheep trampling,and by 23% and 44%,respectively,by yak trampling,compared with their respective values in the control（untrampled）.The magnitude of the increase in soil respiration rate,saturated hydraulic conductivity,and abundance of all three types of microorganisms were all lower under yak trampling than under Tibetan sheep trampling treatments at the same grazing intensity.Overall,soil physical properties and microbe abundance were strongly affected by increased livestock trampling and soil moisture.The soil physical properties at 0-10 cm depth were strongly affected by livestock trampling,and yaks caused greater soil compaction and more negatively affected microorganism distribution than did Tibetan sheep.