关键词: 牦牛, 藏羊, 粪便降解, 养分循环, 高寒草地, 土壤-植物体系

Abstract: The decomposition of yak dung (YD) and Tibetan sheep dung (SD) affects nutrient cycling in alpine grasslands, but the mechanisms underlying the differences in their impacts on plant-soil nutrient cycling remain unclear. In this study, a 270 day decomposition experiment using fresh YD and SD was conducted in an alpine grassland near the Qinghai Lake. By measuring nutrient contents in dung, soil, and plants at different decomposition stages, we analyzed the effects of the two dung types on nutrient transfer along the soil-plant continuum. The results showed that: 1) The decomposition rate of YD was significantly higher than that of SD. Total carbon (TC), total nitrogen (TN), and total phosphorus (TP) in YD decreased linearly over time (TC declined from 333.39 g·kg^-1 to 211.24 g·kg^-1), with TN consistently higher in YD than in SD. After 90 days of decomposition, nitrate (NO₃^--N) and available phosphorus (AP) contents were significantly higher in YD than in SD. 2) Changes in soil TN and TP were mainly influenced by dung type, accounting for 57.1% and 71.5% of the variance, respectively. Soil NO₃^--N and AP under YD treatment remained significantly higher than those under SD throughout the 90 day decomposition period. 3) Plant nutrient uptake showed functional group specificity. Plant functional group was the key factor driving variation in plant TN, explaining 40.2% of the variance. The TN of grasses responded more rapidly under YD treatment than under SD treatment. 4) Structural equation modeling revealed that dung affected plant nutrient uptake mainly through the indirect pathway “dung total nutrients → soil available nutrients”, with soil available nutrients acting as the critical mediator. In summary, yak dung decomposed faster, favoring early release of available nutrients and grass nitrogen utilization, whereas Tibetan sheep dung decomposed more slowly, leading to a more prolonged nutrient release process. This study clarified key processes through which different livestock dung types drive soil-plant nutrient cycling and could provide a scientific basis for optimizing grazing management in alpine grasslands.

Key words: yak, Tibetan sheep, dung decomposition, nutrient cycling, alpine grassland, soil-plant system