不同强度牦牛放牧对青藏高原高寒草地土壤和植物生物量的影响

放牧作为家畜饲养方式之一，是草地最简单、有效的利用方式，放牧中的家畜对草地生态系统的影响是全球畜牧生态学研究的焦点。过度放牧导致草地退化严重，虽然在青藏高原地区已有较多放牧对草地影响的研究，但探究连续4年放牧对高寒草地生态系统影响的定位实验却鲜见报道。本研究在青藏高原东缘选取典型高寒草地，使用高原特有且分布最广的牦牛作为大型草食放牧家畜，设置了4个牦牛放牧强度（禁牧：无放牧、轻牧：1头/hm²、中牧：2头/hm²和重牧：3头/hm²）以研究其对高寒草地土壤和植物功能的影响。开展4年试验后的结果表明：放牧条件下土壤含水率显著增加；而土壤容重、全磷和有机质含量对放牧强度均无显著性响应；土壤全氮和pH的响应主要在表层0-20 cm，其中全氮为轻牧和重牧处理分别显著高于中牧，中牧处理下的土壤pH为显著高于轻牧；土壤全钾含量在禁牧处理中显著高于放牧处理；而土壤有效氮和速效钾均为中牧处理显著高于禁牧；放牧可以显著降低植物地上生物量。牦牛放牧强度显著影响土壤含水率、有效养分和植物地上生物量，而对其它土壤理化性质影响较弱。本研究结果揭示放牧对高寒草地土壤理化性质和植物地上生物量的影响，为青藏高原高寒草甸生态系统保护、可持续管理和合理放牧率提供理论依据。

Effects of different yak grazing intensities on soil and plant biomass in an alpine meadow on the Qinghai-Tibetan Plateau

As one of the most importance ways for supporting herds of domesticated ungulates, grazing is the simplest and most effective way of grassland utilization. The effects of grazing on grassland ecosystem are also one of the classic topics of animal ecology. In recent decades, overgrazing has caused serious grassland degradation. Although some studies have focused on the effects of grazing on grassland ecosystems on the Qinghai-Tibetan Plateau, little information on the effects of yak grazing intensity on alpine grasslands are revealed based on long-term in situ field observations, especially for experiments with more than 4 years. In this study, we selected a typical alpine meadow in the eastern of the Qinghai-Tibetan Plateau and used yaks as our large herbivorous livestock because yaks are unique and most widely distributed on the Qinghai-Tibetan Plateau. According to local investigations and pre-experiment, we set up four yak grazing intensities (no grazing; light grazing, 1 yak/hm²; moderate grazing, 2 yaks/hm²; and heavy grazing, 3 yaks/hm²) to examine their effects on soil properties and plant growth in a typical alpine meadow of the Qinghai-Tibetan Plateau. After continuously conducting four-years experiment, we found that soil water content increased significantly under grazing treatments. Soil bulk density, total phosphorus (P) content and organic matter content showed no significant responses to grazing intensities. Soil total nitrogen (N) content was significantly higher under light and heavy grazing than that under moderate grazing at the top soil of 0-20 cm. Conversely, soil pH was significantly higher under moderate grazing than light grazing at the top soil of 0-20 cm. Soil total potassium (K) content under no grazing was significantly higher than that under grazing treatments. Soil available N and K contents were only significantly higher under moderate grazing than those under no grazing. Grazing also significantly reduced aboveground biomass of plants. In short, yak grazing intensities significantly altered soil water content, soil available N and K contents, and plant aboveground biomass, while they had weak effects on soil organic matter, total N, and total K contents. This study reveals the effects of grazing on soil physiochemical properties and plant aboveground biomass in a typical alpine meadow, though further study should be required to investigate the influences of long-term grazing experiments on the interactions of plants and soil and determine appropriate grassland managements in a long term based on our yak grazing experiments. Overall, this study provides basic data for the protection, sustainable management and reasonable grazing rate of alpine meadow ecosystem on the Qinghai-Tibetan Plateau.