甘南尕海湿地退化过程中土壤氮矿化演变特征及机制

Soil nitrogen mineralization is the primary limiting factor of plant growthin wetland ecosystem, and it is also an important step in nitrogen biogeochemical cycles. It is of great scientific meanings for revealing the process of soil nitrogen mineralization to study the mechanism and evolution characteristics of soil nitrogen mineralization in the alpine wetland. Base on the consistent attention scientific problem of degradation of alpine wetland ecosystem, the project focus on the soil that experienced different degradation stages in Gahai wetland on the eastern Qinghai-Tibet Plateau. Through laboratory incubation, intact soil core in situ, fluorescent quantitative PCR, 15N isotope pool dilution technique, combining with meteorological data and accumulated relevant research data, the project is 1)to study the evolution law of soil nitrogen mineralization potentials, mineralization paths and net mineralization rates in the process of wetland degradation, 2)to illustrate evolvement characteristics of key microbial functional genes and enzyme activity to determine the evolution of soil nitrogen mineralization, 3)to reveal the microbiological and environmental driving mechanism of soil nitrogen mineralization evolution in wetland degradation through establishing the coupled model of "climatic conditions- vegetation and soil biochemical properties-soil nitrogen mineralization" in wetland degradation under climate change background. The results obtained from this project will provide reliable basic data for accurate assessment of soil nitrogen supply capacity and prediction of soil nitrogen mineralization process under the background of future climate change in China's alpine wetland system, The results will also be helpful for the restoration and management of degraded ecosystems in the alpine wetland.

土壤氮矿化是限制湿地生态系统中植物生长的主要因素，也是氮素生物地球化学循环的重要环节。研究高寒湿地系统土壤氮矿化演变规律及机制，对揭示湿地土壤肥力变化过程具有重要的科学意义。本项目针对高寒湿地生态系统退化这一备受关注的科学问题，以青藏高原东缘尕海湿地不同退化阶段的土壤为研究对象，通过室内培养、原位土柱试验、荧光定量PCR、15N同位素稀释等技术手段，结合气象监测数据和已积累的相关研究资料，研究湿地退化过程中土壤氮矿化潜力、矿化途径、净矿化速率的演变规律，探明土壤氮矿化演变的关键微生物功能基因及酶活性变化特征，建立气候变化背景下湿地退化过程的“植被、土壤性状-微生物-土壤氮矿化”耦合关系模型，揭示湿地退化过程中土壤氮矿化变化的微生物及环境驱动机制，为准确评估我国高寒湿地系统土壤氮供给能力和对未来气候变化下土壤氮循环过程的认识提供可靠的基础数据，服务于我国高寒湿地退化生态系统的恢复和管理。

土壤中氮素的吸收、转化及含量变化是影响植被生长的关键因素。高寒湿地退化改变了土壤性状和酶活性，影响着土壤氮的积累及其矿化过程，进而影响湿地生态系统的功能。本项目以青藏高原东缘尕海湿地不同退化阶段的土壤为研究对象，研究湿地退化过程中土壤氮硝化、氨化和矿化速率的动态变化及其影响因素。结果表明：1）湿地退化演替过程中土壤含水量逐渐减小，土壤温度呈先减后增的趋势。2）湿地退化演替过程中土壤硝态氮含量呈增加趋势，而全氮、铵态氮、微生物量氮、未知态氮、酸解铵态氮、酸解氨基酸态氮及氨基糖态氮含量呈减小趋势，尤其在0-10 cm 土层；全氮在5、6月较高，而铵态氮、硝态氮、微生物量氮和酸解氮组分均在7月或8月较高。3) 随退化程度加剧，土壤脲酶、硝酸还原酶活增加，而蛋白酶、亚硝酸还原酶活性降低。4)湿地退化演替过程中氮矿化关键功能基因AOA、AOB、nifH和nirK丰度变化范围为106~108、107~108、105~106和107~108拷贝数/ｇ干土，４种基因丰度均在轻度退化阶段达到最大值，中度和重度退化阶段显著降低。5）湿地退化对土壤氮矿化过程有显著抑制作用，与未退化（0.143 mg kg-1 d-1）相比，轻度退化、中度退化、重度退化的土壤净氮矿化速率分别减小了0.018 、0.025、0.020 mg kg-1 d-1；除未退化阶段土壤净氮矿化速率在8月份出现最大值外，其余各退化阶段最大值均出现在7月份。6）中、重度退化降低了土壤氮矿化潜力，在田间持水量的40% -80% 范围内，土壤氮矿化势表现为未退化、轻度退化高于中度、重度退化；未退化、轻度退化和中度退化矿化势随温度升高显著增大，而重度退化随温度升高先增大后减小。7）土壤含水量、nifH是影响尕海湿地退化过程中土壤氮矿化演变的最主要驱动因素。研究结论对揭示高寒湿地退化过程中土壤环境变化规律有重要意义，并为湿地恢复过程中的氮调控管理供科学依据。