牦牛尿液返还特性对藏北高原冷生土壤N2O排放的影响

Yak urine deposition is an important pathway of nutrient return and redistribution on alpine grasslands in the Qinghai-Tibetan Plateau. Yak urine return may promote soil nitrous oxide (N2O) emission and plant growth through increasing soil available nitrogen and water content, but the effects of yak urine that had temperature and nitrogen concentration differences on soil nitrogen transformation, N2O emission and plant growth remain unknown. The applicant conducted an experiment on the northern Tibetan Plateau preliminary and found the temperature and nitrogen concentrations markedly affect soil N2O emission that amended with fragmented yak dung patches, and the yak urine had temperature and nitrogen concentration differences probably inevitably influence Cryosols N2O emission directly. Therefore, the proposed research is thought to be conducted on typical grasslands by carrying out soil N2O sampling in situ and 15N labeling experiments, to explore the response mechanism of soil nitrogen dynamics, N2O emission, plant growth and its nitrogen stocks to the application of yak urine with temperature and nitrogen concentration interactions. Soil nitrogen transformation rate is detected so as to investigate the effects of yak urine properties on the main nitrogen transformation processes after the urine deposition. The results of this research would help to provide scientific evidences to improve the cognitions in understanding the effects of livestock urine return on natural grasslands soil nitrogen cycles, to optimize the management mode of urine and maintain the sustainable development of alpine grasslands ecosystems.

牦牛尿液排泄是影响青藏高原高寒草地生态系统氮循环的主要因素之一，牛尿施加可能通过增加土壤有效氮和含水量从而促进植物生长和土壤N2O排放，但牛尿温度和氮含量特性对土壤氮转化、N2O排放和植物生长的影响机制尚不清楚。申请人博士期间开展的不同斑块大小牦牛粪便返还对高寒草原土壤N2O排放的研究发现，温度和氮含量是影响土壤N2O排放的重要因子，并认为牛尿温度和氮含量特性将可能对冷生土壤N2O排放产生不容忽视的影响。因此，本项目拟以藏北高原高寒草原为研究对象，通过开展野外土壤N2O原位采集和室内15N同位素标记试验，探究牛尿温度和氮含量交互影响下冷生土壤氮素动态、植物生长及氮储量和N2O排放的响应特征；通过测定土壤氮初级转化速率揭示牛尿返还特性对土壤氮转化关键过程的影响，以期为增加牲畜尿液返还对天然草地土壤氮循环影响的认知、优化牲畜尿液管理模式和维持草地生态系统可持续发展提供科学依据。

放牧牦牛排泄物返还是对青藏高原脆弱高寒草地生态系统天然的施肥措施，对于维持土壤养分平衡和生态系统生产力具有十分重要的生态学意义。探究季节性冻融背景下高寒草地土壤自身及其对放牧牦牛粪尿施加的响应特性，对于揭示外源性氮输入对高寒草地氮素过程和温室气体排放的影响效应、作用机制及差异性具有理论创新价值和实践指导意义。. 本项目以藏北高原季节性冻融高寒草地为研究对象，围绕草地冻融与土壤理化和生物学特性的关系、放牧牲畜尿液特性差异对土壤氮素的短期效应、牦牛尿液和粪便返还特性对其自身降解和草地土壤氮素过程与温室气体排放的作用机制和差异性等内容开展了控制试验和野外定位观测试验，探究了放牧牲畜排泄物返还对高寒草地氮素和地气过程的影响效应。主要结果表明：（1）草地季节性冻融是影响土壤氮素过程不容忽视的背景因素，放牧牛羊排泄物是草地重要的氮素来源且外源性粪尿自身特性和氮素变化对土壤氮转化关键过程和温室气体排放具有重要影响；（2）牛羊尿返还在短期内分别显著增加0-10 cm和10-20 cm表层土壤铵态氮（NH4+-N）和硝态氮（NO3--N）含量，通过改变土壤理化性质、硝化和反硝化过程而影响NH4+-N和NO3--N权衡；牛尿温度和氮含量特性是影响土壤矿化氮含量和氧化亚氮（N2O）排放的重要因素，且通过调控土壤微生物活性改变氮转化过程；（3）牛粪斑块碎化显著增加可溶性有机碳和可溶性有机氮淋溶量，NH4+-N和NO3--N淋溶系数分别介于0.68%-0.87%和0.19%-0.27%，不同碎化程度对牛粪矿化氮含量权衡具有差异性影响；（4）1/8和1/16碎化牛粪显著降低高寒草原土壤N2O排放，较低的反硝化速率导致1/16碎化牛粪N2O排放系数最低（0.002%）；原状牛粪1/16碎化被认为是减少草原土壤N2O排放和增加植被生物量氮含量的有效策略。. 项目研究结论有助于加深关于放牧牲畜粪尿与脆弱草地生态系统氮素生物地球化学循环关系的理论认知，进而为优化牲畜粪尿管理模式、促进高寒草地生态系统高质量和可持续发展等提供有益参考。