高寒草原土壤有机碳矿化对水氮添加的响应

Response of Soil Organic Carbon Mineralization to Water and Nitrogen Addition in Alpine Steppe

[目的]研究不同水氮添加下的高寒草原土壤有机碳矿化过程,探讨土壤性质与土壤碳矿化的关系,为揭示全球变化背景下高寒草原土壤碳转化规律提供科学依据.[方法]设置45%,60%,75%,90%的田间持水量(WHC)4个水分梯度和4个氮添加梯度(0,0.2,0.4,0.8 mg/g)进行室内培养,分析CO2浓度,测定土壤溶解性有机碳(DOC)、土壤微生物生物量碳(MBC)含量以及土壤酶活性.[结果]①在水或氮添加范围内,土壤有机碳矿化量呈抛物线变化趋势,土壤碳矿化受水分调控更加敏感,氮添加对土壤碳矿化的影响依赖于水分添加量.②土壤水分从45%增加到60%WHC,加速了土壤中可溶性物质溶出,增加了有机碳矿化;施氮量从0 mg/g增加到0.4 mg/g,土壤有机碳含量、土壤微生物量碳含量呈上升趋势,刺激了土壤有机碳的矿化.③90%田间持水量WHC的高水分添加与45%田间持水量土壤水分下的高氮添加(0.8mg/g)抑制高寒草原土壤碳矿化,高水分添加通过降低土壤通透性抑制有机碳矿化过程,高氮添加通过降低土壤DOC生物有效性、土壤MBC含量、土壤酶活来抑制土壤有机碳矿化过程,高氮添加对碳矿化的抑制作用在90%WHC条件下得到缓解.[结论]随着未来氮沉降量与降雨量的持续增加,青藏高原高寒草原土壤有机碳的矿化作用可能会受到抑制,有利于高寒草原土壤有机碳积累.

[Objective]The mineralization processes of soil organic carbon under different water and nitrogen additions were studied to understand the relationship between the soil properties and carbon mineralization,and to provide scientific references for revealing the soil carbon conversion pattern in alpine steppe under global change.[Methods]A laboratory experiment was conducted with four different soil water contents(45%,60%,75%,90%water-holding capacity,WHC)and four nitrogen levels(0,0.2,0.4,0.8 mg/g).The following parameters were measured:CO 2 concentration,dissolved organic carbon(DOC),microbial biomass carbon(MBC)content,and enzyme activity.[Results]①Within the experimented range of water and nitrogen addition,carbon mineralization volume showed a parabolic pattern.Soil carbon mineralization was more sensitive to the addition of water and the effect of the nitrogen addition on soil carbon mineralization was dependent on the water content.②Increasing the water content from 45 to 60%WHC led to a faster leaching of the soluble substances from the soil,indicating a greater carbon mineralization.The soil organic carbon and microbial biomass carbon also showed an upward trend with an increase of the nitrogen addition from 0 to 0.4 mg/g.③The soil carbon mineralization was inhibited either with the high WHC(90%)or by the addition of a higher content of nitrogen(0.8 mg/g)at 45%WHC.The high water content led to a lower soil carbon mineralization by a reduction in the soil porosity;whereas the addition of a high nitrogen content(0.8 mg/g)led to the inhibition of the soil carbon mineralization process by decreasing the availability of the DOC of the soil,level of MBC in the soil,and activity of soil microbial enzyme.The carbon mineralization inhibition by high-content nitrogen addition was alleviated at a high WHC(90%).[Conclusion]The predicted continuous increase in nitrogen deposition and precipitation in the Tibet Plateau may inhibit the carbon mineralization processes of the alpine steppes and benefit the accumulation of soil organic carbon.