高寒草毡层基本属性与固碳能力沿水分和海拔梯度的变化

Variation in basic properties and carbon sequestration capacity of an alpine sod layer along moisture and elevation gradients

高寒草毡层是高原寒区自然植被下形成的松软而坚韧且耐搬运的表土层,认识其生态功能是促进草牧业生产休养保护和工程施工主动利用的前提。通过对青藏高原东部若尔盖高原植被的广泛调查,在布设沼泽、退化沼泽、沼泽化草甸、湿草甸、干草甸和退化草甸水分梯度群落样地,以及亚高山草甸、亚高山灌丛草甸、高山灌丛草甸和高山草甸海拔梯度群落样地的基础上,通过对不同类型群落样地草毡层容重、土壤颗粒组成和土壤有机碳(SOC)含量的测定分析,比较了水分和海拔梯度下草毡层固碳能力。结果表明,草毡层厚度平均为30cm,沼泽湿地草毡层容重最小,SOC含量在300g/kg以上;退化草甸容重最高,SOC含量显著下降。不同群落草毡层SOC密度在10—24kg C/m^2之间,随着土壤水分有效性的降低而降低;高山灌丛草甸草毡层SOC密度比草甸高15%。研究得出,保持草毡层稳定的质量含水量阈值为30%,SOC含量阈值为30g/kg;高寒植被草毡层在沼泽到草甸的退化演替中,容重、紧实度变大,有机碳含量减少,碳密度和碳储量下降;灌丛草甸的固碳能力大于草甸,但灌丛草甸的生产功能降低;保持可持续发展的草地生产能力,维护固碳生态功能,需要防止草毡层退化,抑制草甸向灌丛草甸演替。

The alpine sod layer is spongy, tough, and resistant to the shifting surface soil layer formed under natural vegetation in the alpine cold region. Understanding the ecological functions of this layer is necessary to promote sustainable methods of grass production and animal husbandry that can restore and protect existing grasslands, and to suggest new projects to implement these goals. After conducting extensive preliminary investigations regarding the alpine vegetation on the Zoige Plateau on the Eastern Qinghai-Tibetan Plateau, China, we established community sample plots along the existing soil moisture gradient：swamp, degraded swamp, swampy meadow, wet meadow, dry meadow, and degraded meadow. We also established community sample plots along the existing elevation gradient：subalpine meadow, subalpine shrub meadow, alpine shrub meadow, and alpine meadow. We determined sod layer thickness, bulk density, soil particle composition, and soil organic carbon （SOC） content in the community plots to compare carbon sequestration capacity along the moisture and elevation gradients. The results indicated that the average thickness of the sod layer was 30cm. The bulk density of swamp soil was the lowest among the communities studied, and the SOC content of swamp soil was greater than 300g/kg. The bulk density of degraded meadow soil was the highest among the communities studied, and the SOC content of degraded meadow soil was significantly lower than that of the other communities. The SOC density of the different communities ranged from 10 to 24kg C/m2, and decreased with decreasing soil water availability. Degraded meadow soil had significantly lower SOC storage in the sod layer. The SOC density of alpine shrub meadow soil was 15% higher than that of alpine meadow soil. The minimum mass water content needed to maintain a stable sod layer was 30%, and the minimum SOC was 30g/kg. In alpine vegetation regressive succession, the bulk density and compactness of the sod layer became increased. SOC content, density, and storage decreased along the soil moisture gradient from swamp to degraded meadow. The higher the gravel content of swamp soil, the more easily it was degraded. Similarly, the higher the sand content of meadow soil, the more easily it was degraded. The carbon sequestration capacity of alpine shrub meadows was greater than that of alpine meadows; however, the productivity of shrub meadows was lower. To maintain sustainable development of grassland production and protect the carbon sequestration function of the alpine sod layer, it is necessary to prevent degradation of the sod layer and prevent succession from meadows to shrub meadows.