干化-干湿转化对鄱阳湖湿地土壤氮矿化的影响

本研究采集鄱阳湖湿地3种典型植被(虉草、苔草、芦苇)土壤,在室内分别设置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~(15)N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.土壤干化过程中,芦苇带土壤总氨化速率最高,虉草带土壤总硝化速率最高;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;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.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内变化较小,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内明显增大;3种植被土壤总硝化速率都在1 d内明显下降,此后维持较低水平.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.

Effect of drying-rewetting on soil nitrogen mineralization in Poyang Lake Wetland

In this study, three typical soils from Carex, Phalaris and Phragmites zones in Poyang Lake wetland were collected, and the soil samples were incubated in laboratory for a month under three moisture levels:30%WHC (maximum water-hold capacity) representing severe drought, 50%WHC representing mild drought and 80%WHC representing suitable moisture condition. Then the three moisture levels were adjusted to 200%WHC to simulate rewetting event. Gross ammoniation rate and gross nitrification rate in wetland soil during the drying-rewetting process were calculated based on the ¹⁵N isotope dilution method. In the drying process, the gross ammoniation rate in the soil from the Phragmites zone was the highest, and the gross nitrification rate in the soil from the Carex zone was the highest. Both the gross ammoniation rate and the gross nitrification rate in three typical soils decreased with the increase of drought degree, while the gross nitrification rate dropped more than the gross ammoniation rate under mild drought condition. In addition to the water condition, the gross ammoniation rate was mainly affected by the soil carbon content, and the gross nitrification rate was mainly affected by the pH value. In the rewetting process, the gross ammoniation rate and the gross nitrification rate in soils from the Phalaris and Phragmites zone changed little on the 1st day, then decreased continuously during the 1~5 days. The gross ammoniation rate in the soil from the Carex zone under severe drought maintained an upward trend after rewetting, and that under mild drought only increased on the 1st day after rewetting. All the total nitrification rates in three typical soils decreased significantly on the 1st day after rewetting, and remained low thereafter. The ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) abundance had similar effects on the gross nitrification rate in the drying process, while the AOB abundance had relatively larger effect than the AOA abudance in the wetting process.