滇西北高原纳帕海湿地土壤氮矿化特征

采用树脂芯原位培育法，研究了纳帕海沼泽、沼泽化草甸和草甸土壤氮的矿化特征。结果表明，铵态氮（NH₄⁺-N）为沼泽、沼泽化草甸土壤中无机氮的主要存在形式，分别占无机氮含量的96.76%和75.24%，而硝态氮（NO₃^--N）为草甸土壤中无机氮的主要存在形式，占无机氮含量的58.77%。植物生长期内，纳帕海湿地土壤的净氮矿化速率表现为沼泽化草甸 > 草甸 > 沼泽，表明干湿交替的土壤环境更利于土壤氮矿化作用的进行，土壤中氮素有效性和维持植物可利用氮素的能力更强。整个生长季，沼泽和草甸土壤氮矿化为硝化作用，而沼泽化草甸土壤氮矿化为氨化作用。土壤硝态氮含量、有机质含量、碳氮比和含水量均对纳帕海沼泽、沼泽化草甸和草甸土壤的氮矿化产生显著影响。

Net nitrogen mineralization in soils of Napahai wetland in Northwest Yunnan

Nitrogen (N) is an essential nutrient of special importance for plant growth while it is often deficient in soils because of low phytoavailability. Shifts in soil N status can be caused by variations in the N transformation. Soil N mineralization is of prime importance in ecosystem productivity, N potential availability and losses from ecosystems. Using resin-core incubation method, we examined the net N mineralization rates in swamp, swamp meadow and meadow soils (0-15 cm) in situ. The soils located along a water level gradient in Napahai wetland, which are sensitive to the changes of hydrological regimes, and reflect the different stage of wetland succession. The objective was to provide insight into the mechanism that how wetland ecosystem evolution constraining net N mineralization in soils. The results indicated that the inorganic N concentrations were significantly different among the three soils (0-10 cm), swamp > swamp meadow > meadow, during the growth season. The NH₄⁺-N concentrations showed the same decrease trend as inorganic N while the NO₃^--N concentrations showed a significant increase trend in the three soils., The inorganic N was mainly in the form of NH₄⁺-N in swamp and swamp meadow soils, which accounted for 96.76% and 75.24% respectively. In contrast, NO₃^--N was the main form of inorganic N in meadow soil and accounted for 58.77%. The net N mineralization rates were significantly different during the growth season, ranking in order of swamp meadow > meadow > swamp. The results indicated that wet and dry alternation is beneficial to the net N mineralization in the wetland soils, and favors higher N effectiveness and greater phytoavailability. The net N mineralization rate in swamp soil was negative during the growth season. The rates in swamp meadow and meadow soils were negative from May to September while positive from September to November. The net ammonization rates in the soils showed a significant decrease as meadow > swamp meadow > swamp from May to September, but showed a significant increase as swamp < meadow < swamp meadow from September to November. The net nitrification rates in soils among the three wetland types showed a significant decrease as swamp > swamp meadow >meadow from May to September, but showed a significant increase as swamp < swamp meadow < meadow from September to November. On the whole, the net N mineralization was main in the form of nitrification in the swamp and meadow soils while in the form of ammonization in the swamp meadow soil during the growth season. In addition, the N mineralization in soils was influenced by soil NO₃^--N concentration, organic material concentration, C/N ratio and soil moisture in the soils. The net N mineralization rate in swamp soil was negatively related to soil NO₃^--N concentration, organic material concentration, C/N ratio and soil moisture. In swamp meadow soil, the N mineralization rate was negatively related to soil NO₃^--N concentration and C/N ratio, but was positively related to soil moisture. In contrast, the net N mineralization rate in meadow soil was negatively related to soil NO₃^--N concentration and bulk density, but was positively related to organic material concentration and soil moisture.