生命科学学院知识库

土壤是陆地生态系统最大的有机碳库。不同的土地利用方式和施肥通过改变 土壤有机碳输入与输出的平衡进而影响土壤有机碳储量，而土壤有机碳储量的微 小变化将会对全球气候变化产生重要影响。本文研究不同土地利用方式和施肥如 何改变青藏高原高寒草甸植物与土壤理化性质进而对土壤有机碳储量产生影响。 目的是为选择合适的土地利用方式和施肥措施提高植物生产力和维持土壤碳库 功能提供理论依据。本文选择研究区典型的土地利用方式（围栏封育天然草甸、 中度放牧草甸、农耕地和弃耕地）和施肥措施（对照和不同剂量的单施氮肥、单 施磷肥和氮磷合施），测定了不同土地利用方式和施肥处理下的植物生物量及碳 氮磷、表层土壤碳组分和氮磷以及理化性质。结果如下 ：

1) 农耕显著降低土壤容重和 pH 值；单施氮肥增加土壤容重，降低 pH 值。2) 四种土地利用方式下，植物地上碳储量占总的有机碳储量的 0.7% - 1.7%，且 在围栏封育天然草甸占比最大，根系碳储量占比是 2.5% - 4.3%，且最高占比 在中度放牧草甸；不同施肥处理下，植物地上碳储量占总的有机碳储量的 0.57% - 2.35%，而根系碳储量占比是 2.01% - 3.89%，最大占比均是在中剂量 单施氮肥。3) 中度放牧显著增加土壤微生物量碳，而农耕与弃耕显著降低土壤微生物量 碳；中度放牧、农耕和弃耕均显著降低土壤累积碳矿化量；施肥降低土壤微 生物量碳和累积碳矿化量。4) 农耕显著降低土壤有机碳储量；与不施肥的对照相比，中、高剂量单施氮肥 和中剂量单施磷肥处理下，土壤有机碳储量分别增加 3.92%、 2.32%和 0.45%， 而其他施肥处理下，土壤有机碳储量降低 0.66% - 6.64%。5) 弃耕降低植物地上碳氮比，增加根系碳氮比、植物和土壤氮磷比；低剂量单 施氮肥与高剂量氮磷合施显著降低根系和土壤碳氮比；单施氮肥显著增加植 物氮磷比，而施磷肥则降低植物氮磷比；施肥降低土壤氮磷比。    

总之，在青藏高原高寒草甸，不同土地利用方式和施肥改变植物的生产力、 碳浓度、碳氮比和氮磷比，以及土壤理化性质和微生物特性，进而导致了中度放牧、弃耕、中剂量与高剂量单施氮肥下具有较高的土壤有机碳储量，而农耕和施 磷肥则降低土壤有机碳积累。这些结果可以为选择合适的土地利用方式和施肥措 施提高植物生产力、维持土壤碳库功能提供理论依据。

Soil is the largest organic carbon (C) pool in terrestrial ecosystems. Different land use types and fertilizations can affect soil organic C (SOC) storages by altering a dynamic equilibrium between C input and output. Minor changes in SOC storages will have a great influence on global climate. In this paper, we studied how different land use types and fertilization changed plant and soil physicochemical properties and then changed SOC storages in alpine meadows on the Qinghai – Tibetan Plateau. The objective was to provide theoretical basis for choosing proper land use types and fertilization treatments to improve plant productivity and maintain soil function as C pool. We chose typical land use types (fenced meadow, moderately grazed meadow, tilled cropland and abandoned croplands) and fertilization practices (control treatment and different rates of single nitrogen (N) fertilization, single phosphorus (P) fertilization and both N and P fertilization respectively). We investigated plant biomass and C, N and P, soil C fractions, N, P and soil physical and chemical properties in top profile under different land use types and fertilization treatments. Results showed that:  

1) Tillage significantly decreased soil bulk density and pH; single N fertilization increased soil bulk density, but reduced pH.2) Among four land use types, above-ground C storages took up 0.7% - 1.7% of total organic C storages, with the highest at fenced meadow and proportions of root C storages ranged from 2.5% to 4.3%, with the highest at moderately grazed meadow; the percentages of C storages are 0.6% - 2.4% in above-ground and 2.0% - 3.9% in root, with the highest at medium rate of single N fertilization.3) Moderately grazing notably increased soil microbial biomass C (MBC) while tillage and abandonment decreased MBC; moderately grazing, tillage and abandonment all lowered soil cumulative C mineralization; fertilization decreased soil MBC and cumulative C mineralization. 4) Tillage reduced SOC storages; medium and high rate of single N fertilization and medium rate of single P fertilization increased 3.9%, 2.3% and 0.5% of SOC storages as compared to the control treatment respectively, while other treatments decreased 0.7% - 6.6%.  5) Abandonment decreased above-ground C/N, but increased root C/N, plant and soil N/P; low rate of single N fertilization and high rate of NP fertilization notably decreased root and soil C/N; single N fertilization significantly increased plant N/P, while P fertilization lowered plant N/P; fertilization reduced soil N/P.

To sum up, in alpine meadow, different land use types and fertilization treatment altered plant productivity, C concentration, C/N, N/P and soil physico-chemical and microbial characteristics, and resulted in higher SOC storage in moderately grazing, abandonment, medium and high rate of single N fertilization, while tillage and P fertilization lowered SOC storage. These results could provide theoretical basis for choosing proper land use types and fertilization treatments to guarantee plant productivity and recover and maintain SOC sequestration function.