干旱与旱涝急转对鄱阳湖湿地土壤氮循环的影响

Poyang Lake is a fresh water wetland system with rich biodiversity, and also a hotspot for storage and transformation of regional nitrogen. In recent years, drought and drought-flood abrupt alteration occur frequently in the Poyang Lake Region due to human activities and climate changes, but how this environmental changes affect the nitrogen cycle in wetland soil is still unknown. In this project, three typical vegetation soils in the Poyang Lake wetland are going to be sampled for moisture controlling experiments to simulate the drought with different degrees and the drought-flood abrupt alteration. The soil microbial characteristics, including microbial biomass, functional genes associated with nitrogen cycle and microbial community structure will be monitored during the drying-rewetting process, together with the soil physico-chemical properties. Based on a 15N tracing laboratory experiment, gross N mineralization, gross nitrification, ammonium immobilization, nitrate immobilization and denitrification rates in the wetland soil during the drying-rewetting progress will be calculated using the 15N tracing model. The influences of different drought degrees on nitrogen cycling rates, soil inorganic nitrogen and N2O emission during the drying-rewetting progress will be analyzed. The influences of soil physico-chemical properties and microbial communities on nitrogen transformation will be illustrated under the drought and drought-flood abrupt alteration environment. The research results of the project will clarify the mechanisms of drought and drought-flood abrupt alteration’s impacts on soil nitrogen pools in Poyang Lake wetland, which can provide a scientific basis for Poyang Lake wetland conservation.

鄱阳湖是生态多样性丰富的淡水湿地系统，也是区域氮素储存和转化的重要环节。受人类活动和气候变化影响，近年来鄱阳湖地区干旱和旱涝急转灾害频繁发生，但这种环境变化对湿地土壤氮循环的影响尚不清楚。本课题采集鄱阳湖湿地3种典型植被土壤，进行室内水分控制实验模拟不同等级干旱环境和旱涝急转环境，监测土壤干化-干湿转化过程土壤理化性质和微生物特征（微生物量、氮循环功能基因和微生物群落结构）的变化。通过15N同位素添加实验，基于同位素示踪模型计算湿地土壤干化-干湿转化过程中的总矿化速率，总硝化速率，NH4+固定速率，NO3-固定速率和反硝化速率；分析不同干旱等级对干化-干湿转化过程土壤氮循环速率、无机氮含量和N2O释放量的影响；阐明干旱及旱涝急转环境下土壤理化性质和微生物特征对氮循环过程的影响。研究成果可揭示干旱及旱涝急转环境对鄱阳湖湿地土壤氮循环的影响机理，为鄱阳湖湿地保护提供科学依据。

受人类活动和气候变化影响，鄱阳湖地区干旱和旱涝急转灾害频繁发生，但这种环境变化对湿地土壤氮循环的影响尚不清楚。本研究采集鄱阳湖湿地3种典型植被（虉草、苔草和芦苇）土壤，在室内设置30%WHC（最大持水量），50%WHC和80%WHC 3种水分条件培养1个月，分别模拟重度干旱、轻度干旱和适宜水分环境，然后添加水分到200%WHC模拟干湿转化过程。基于15N同位素稀释法计算干化-干湿转化过程中湿地土壤的总氨化速率和总硝化速率。干化培养30 d后，3种水分条件下总氨化速率均为芦苇带土壤最高（9.08~13.30 mg·kg-1·d-1），其次为苔草带（2.16~4.85 mg·kg-1·d-1），虉草带最低（0.68~2.89 mg·kg-1·d-1）。3种植被土壤总硝化速率变化范围为0.71~24.05 mg·kg-1·d-1。土壤总氨化速率和总硝化速率都随干旱程度增强而降低，轻度干旱条件下总硝化速率的降低比总氨化速率更明显。与适宜水分条件（80% WHC）相比，鄱阳湖湿地3种植被土壤总硝化速率在重度干旱（30% WHC）和轻度干旱（50% WHC）条件下都显著降低；但与轻度干旱相比，重度干旱下只有虉草带土壤总氨化速率显著降低。土壤湿化过程中，苔草带和芦苇带土壤氮总氨化速率在1 d变化较小，1~5 d不断下降；虉草带重度干旱土壤氮总氨化速率在湿化后呈上升趋势，轻度干旱土壤只在湿化后1 d明显增大；3种植被土壤总硝化速率都在1 d明显下降，此后维持较低水平。干旱条件下，细菌和真菌群落多样性随干旱程度增加而降低，旱涝急转后，细菌群落多样性呈先降后增的趋势，真菌群落呈先增后降的趋势。除水分条件外，总氨化速率主要受土壤碳含量影响，总硝化速率主要受pH值影响。干化过程中，氨氧化古菌（AOA）和氨氧化细菌（AOB）丰度对土壤总硝化速率的影响相近，湿化过程中AOB丰度的影响相对增大。研究中未发现细菌和真菌群落结构，以及反硝化功能基因（nirK、nirS和nosZ）丰度对湿地土壤总氨化速率和总硝化速率有显著影响。研究成果揭示了干旱及旱涝急转环境对鄱阳湖湿地土壤氮循环的影响机理，为鄱阳湖湿地保护提供科学依据。