高寒人工草地土壤可溶性有机氮库和无机氮库动态变化

Dynamics of Soil Dissolved Organic Nitrogen and Inorganic Nitrogen Pool in Alpine Artificial Grasslands

以青海省高寒区人工草地为研究对象,分析土壤可溶性有机氮库和无机氮库含量及其季节动态变化过程,确定牧草不同发育期土壤供氮能力,为研究高寒区人工牧草吸收土壤氮素提供依据.研究结果表明,（1）青海同德暗栗钙土种植禾本科牧草第1 年土壤以硝态氮为主,占54%-59%,其次为可溶性有机氮,占22%-29%,铵态氮最低,仅占17%.1 年人工草地土壤铵态氮含量随生长季延长逐渐增多,9 月最高;土壤硝态氮在6 月返青期最高,随生长季延长下降显著;土壤可溶性总氮和可溶性有机氮在返青期和枯黄期较高,生长旺盛期较低.（2）青海果洛州退化高寒草甸土种植禾本科牧草的人工草地土壤硝态氮和可溶性有机氮占优势,分别占49%和43%,铵态氮仅占8%.1 年人工草地随生长季土壤铵态氮含量逐渐升高,9 月最高;土壤硝态氮在7 月初期最高,随生长季延长显著下降;土壤可溶性总氮和可溶性有机氮在生长季初期（7 月）最高,随生长季延长而降低.表明高寒区人工草地土壤可溶性有机氮是植物可利用氮的重要组成成分,其含量仅次于硝态氮且远高于铵态氮.（3）与1 年人工草地相比较,同德单播禾本科牧草生长3 年后,土壤中植物可利用氮素迅速下降,尤其是硝态氮含量下降近80%,其次铵态氮下降近67%,可溶性总氮下降近60%2.5 倍,仅可溶性有机氮下降不显著.说明单播模式下人工草地土壤有效养分下降是人工草地生产力难以持续的主要原因.（4）在1 年人工草地种植的不同牧草种类的土壤各类氮素均无显著差异;而在3 年草地,冷地早熟禾（Poa crymophila）和星星草（Puccinellia tenuiflora）单播人工草地土壤表层硝态氮显著高于其他种单播人工草地,星星草和多叶老芒麦（Elymus sibiricus）单播人工草地土壤可溶性总氮显著高于其他种类人工草地.初步推断：种植不同牧草可对不同形态土壤氮素产生影响,暗示不同牧草对不同形态氮素的需求存在-定差异性.

This research was carried on alpine artificial grasslands in Qinghai Province. The soil dissolved organic nitrogen, soil inorganic nitrogen content and their season dynamics were analyzed, and the soil N-supplying capacity of different time was determined. This study will lay the foundation for alpine artificial grassland plants to absorb soil nitrogen. The results showed, (1) For dark chestnut soil of one year’s artificial grassland in Tongde County, soil NO3-N was most dominant and account for 54%~59% of the soil dissolved total nitrogen. The second was soil dissolved organic nitrogen and account for 22%~29%. The third is soil NH4+-N and only account for 17%. Soil NH4+-N content was increasing with growth season and up to maximum in September. Soil NO3-N was maximum in June and was decreasing with growth season. Soil dissolved total nitrogen and dissolved organic nitrogen was higher in turning green period and withering period than in thriving period. (2) For degraded alpine meadow soil of one year’s artificial grassland in Guoluo County, soil NO3-N and dissolved organic nitrogen were dominant and account for 49% and 43% of the soil dissolved total nitrogen respectively. soil NH4+-N only account for 8%. The season dynamics of soil NO3-N and NH4+-N in Guoluo County was similar with Tongde County. Soil dissolved total nitrogen and dissolved organic nitrogen was higher in July then was decreasing with growth season. So the dissolved organic nitrogen was a important compoant in alpine meadow soil, and its content was next to soil NO3-N and far higher than NH4+-N. (3) Compared with one year’s artificial grassland, soil available nitrogen was falling rapidly in three year’s artificial grassland. Such as soil NO3-N content decreased nearly 80%, soil NH4+-N decreased nearly 67%. Only there was no significant decline for soil dissolved organic nitrogen content. So, The decline of soil available nutrient was main reason for decline of artificial grassland productivity. (4) There was no significant difference for nitrogen content of different type among one year’s artificial grasslands with different forages. But in three year’s artificial grasslands, soil NO3-N contentseededPoa crymophila andPuccinellia tenuiflora was significant higher than that seeded other forages, and soil dissolved total nitrogen content seededPuccinellia tenuifloraandElymus sibiricus grasslands was significant higher than that seeded other forages. Therefore, plant species seeded would impact on soil nitrogen and different forage had difference for soil nitrogen requirement.