三江源区高寒草甸草场植被和土壤对外源氮素输入的响应

The typical alpine meadow vegetation and soil is as the research object in three-river area of Qinghai-tibet plateau, the three regions of routine observation zone, micro zone and fertilizing zone are established in moderate degraded alpine meadow pasture in three-river area . The fertilization, sampling and sample analysis are implemented in grass growing season. Through seasonal sampling analysis of nitrogen nutrient of soil -grass chamber in alpine meadow pasture, understanding nitrogen distribution and seasonal dynamics in soil - vegetation system. Choosing different type of nitrogen fertilizer, using the 15N isotope tracer method, tracing fertilizer distribution in the soil - vegetation system , utilization rate of nitrogen of different type of fertilizer are determined in alpine meadow grassland, the nitrogen fertilizer types with low residue, high utilization rate, suitable for application in this region are screened . The profit and loss of soil nitrogen under different nitrogen input in alpine meadow are studied. The dynamic change characteristics of nitrogen of vegetation and soil are monitored in the growing season, the profit and loss amount of nitrogen and exogenous nitrogen input amount in different period are determinate. On the basis of the above research work, the nitrogen fertilization application scheme with low residue, high utilization rate are put forward in alpine meadow pasture in Three-River Source area.

本项目以青藏高原三江源区典型高寒草甸植被和土壤为研究对象，在三江源区中度退化高寒草甸草场设定常规观测区、微区和施肥区三个大区，在牧草生长季开展施肥、采样和样品分析工作。通过对三江源高寒草甸草场土壤-牧草分室的氮素养分的季节性采样分析，掌握氮素在三江源高寒草甸土壤-植被系统中的分配及季节动态。选择不同氮素形态的肥料，采用同位素15N示踪法，通过示踪肥料在土壤-植被系统中的分配情况，确定不同肥料形态的氮素在三江源高寒草甸草场的利用率，筛选出适合本区域应用的低残留、高利用率的氮素肥料类型。 通过开展不同氮素输入量下三江源高寒草甸土壤氮素表观盈亏研究，监测生长季内植被及土壤内的氮素动态变化特征，确定不同时间段的氮素表观盈亏量及外源氮素的输入量。在上述工作的基础上，提出三江源区高寒草甸草场低残留、高利用率的氮肥施用方案。

研究氮素在三江源区高寒草甸草场土壤-植被之间的迁移和相互作用，明确三江源区高寒草甸草场土壤和牧草的氮素季节性供需状况，确定外源氮在高寒草甸土壤-植被系统内的去向，通过明确三江源高寒草甸草场牧草生育期间牧草及土壤氮素的时空变化特征，对牧草生育期不同阶段土壤氮素的盈余与亏缺进行了表观估算，为基于不同利用方式(生产型和生态型)下的三江源高寒草甸草场氮素合理施用提供理论依据。研究发现三江源区高寒草甸草场牧草与土壤中的氮素季节变化趋势表现不一；不同形态氮素在氮素添加两年后残留在土壤中氮素会继续被植物吸收用，植被回收率为 6.26%～29.81%，土壤中残留氮素为 3.75%～19.54%，损失率为 9.92%～26.58%，进一步确定了在高寒草甸草场能提高氮素利用率的最佳氮素形态是酰胺态；在三江源区高寒草甸中以生产效益为主时可选择施氮量为45g·Nm -2酰胺态氮，此时草地生物量达到最大值且草地生态系统处于稳定的状态；而以生态效益为主时可选择施氮量为30g·Nm -2的酰胺态，此时的草地物种较为丰富，植物及土壤养分含量较高。