青藏高原东部高寒草甸草地土壤物理性状对氮元素添加的响应

依托设置于青藏高原东部夏河县桑科草原的天然草地刈割型草场培育定位试验，探讨不同氮元素添加量对高寒草甸草地土壤物理性状的影响。本试验共设4个处理，分别为对照（CK，0 kg N／hm2）、低氮（LN，50 kg N／hm2）、中氮（MN，100 kg N／hm2）、高氮（HN，150 kg N／hm2）。通过对高寒草甸草地土壤容重、孔隙度、紧实度、土壤团聚体等物理性状进行测定与分析，结果表明，MN 与 HN 处理可显著降低0～10 cm 土壤容重与土壤紧实度、增加土壤总孔隙度、非毛管孔隙度与最大持水量。20～30 cm 土层中 LN、MN、HN 处理均可显著增加土壤容重、土壤紧实度，降低土壤总孔隙度、最大持水量。对土壤团聚体的影响，与 CK 处理相比 MN、HN 处理可显著提高各土层≥0．25 mm 机械稳定性土壤团聚体含量、提升土壤团聚体平均重量直径（MWD）；较之 CK 处理，LN、MN处理可显著提升各土层≥0．25 mm 水稳性团聚体含量，同时不同氮元素添加处理均可显著提升水稳性团聚体和MWD，表明氮元素添加对该区土壤侵蚀性有较好的抑制作用，进而减少水土和养分的流失。对地上和地下生物量的影响，MN、HN 处理能显著提升草地地上生物量；MN 处理显著增加了地下生物量、HN 处理显著降低了地下生物量；LN 处理对地上与地下生物量的影响不显著。通过试验得出结论 MN 处理对土壤物理性状的改善效果较好，该处理改善了土壤容重、孔隙度及土壤紧实度，提高了土壤干筛≥0．25 mm 机械稳定性团聚体与湿筛≥0．25 mm水稳性团聚体含量及其稳定性（MWD），增加了草地地上生物量和地下生物量。

Effects of nitrogen addition on the physical properties of soil in an alpine meadow on the eastern Qinghai-Tibetan Plateau

A 3-year study was conducted from 2012 to 2014 to determine the effects of nitrogen (N)addition on the physical properties of soil in an alpine meadow in Xiahe County on the eastern Qinghai-Tibetan Plateau.The four treatments were as follows:CK (control,no N addition),LN (low N,50 kg N/ha),MN (medium N,100 kg N/ha),and HN (high N,150 kg N/ha).Each N-addition treatment had three replicates of 54 m2 (6 m×9 m),with a 1.5 m isolation band between adjacent plots.Analyses of soil bulk density,soil porosity,soil compaction,and soil aggregates showed that MN and HN treatments reduced soil bulk density and soil compac-tion,increased soil porosity and non-capillary porosity,and maximized water-holding capacity in the 0-10 cm soil layer.In the 20-30 cm soil layer,compared with CK,all N-addition treatments showed higher soil bulk density and soil compaction,reduced soil porosity,and maximized water-holding capacity.In terms of the effect of N addition on the stability of soil aggregates in the 0-30 cm soil layer,the LN,MN,and HN treat-ments dramatically increased the macro-aggregate content (≥0.25 mm)and MWD (mean weight diameter), with the MN treatment having the strongest effect.Compared with CK,LN and MN dramatically improved the water-stable aggregate content.All of the N-addition treatments significantly promoted soil aggregation and in-creased the MWD of aggregates.The results indicated that N addition could effectively prevent soil erosion, and hence,control the loss of water and soil nutrients.The MN and HN treatments significantly increased the aboveground biomass in the grassland,while underground biomass was increased in the MN treatment and de-creased in the HN treatment.The results of this study showed that the MN treatment was the most beneficial treatment in terms of improving soil properties.This treatment increased soil bulk density,reduced soil porosi-ty,and increased soil compaction,increased the content of ≥0.25 mm soil aggregates and improved aggregate stability,and increased both the aboveground and underground biomass of plants in the grassland.