三江源区退化天然草地和人工草地生物量碳密度特征

生物量碳密度是生态系统表征碳截存能力的重要功能特征之一。为明晰三江源区高寒草地生物量碳密度特征,选取源区内3个县（玛沁县、甘德县、达日县）的退化天然草地（黑土滩）、退化人工草地、未退化天然草地为研究对象,通过野外调查取样和室内分析相结合的方法,对样区地上生物量、根系生物量及其碳密度进行测定与分析。结果表明：“黑土滩”地上生物量高于退化人工草地和天然草地;“黑土滩”活根和死根生物量都低于天然草地和退化人工草地。退化人工草地、“黑土滩”和天然草地的总生物量碳密度分别为719.47、706.57和2 233.09 g/m²。草地退化不仅改变了生态系统的生物量分配,而且改变了地上部分、活根和死根中的碳密度分配比例。退化人工草地和天然草地的活根和死根碳密度占总生物量碳密度的90%以上,“黑土滩”活根和死根碳密度占79.41%。活根碳密度与总生物量碳密度的比值在3种不同草地群落间的变化较地上植被和死根的大,因此,活根碳密度比例可以作为草地退化的敏感指标。

Characteristics of Biomass Carbon Density of Degraded Natural Grassland and Artificial Grassland in the “Three-River Headwaters” Region

Biomass carbon density is one of the important features of carbon sequestration ability in ecological system. To describe the characteristics of biomass carbon density in alpine grassland in the “Three-River Headwaters” region, above ground biomass, living root biomass, dead root biomass and their carbon content in black soil land and natural grassland were measured. The results showed that the aboveground biomass in black soil land was higher than the aboveground biomass in degraded artificial grassland and natural grassland; but the living root biomass and dead root biomass in black soil land were lower than the living root biomass in degraded artificial grassland and natural grassland. The total biomass carbon density in degraded artificial grassland, black soil land and natural grassland was 719.47, 706.57 and 2 233.09 g/m², respectively. Grassland degradation not only changed ecosystem biomass allocation, but also changed the carbon density distribution in aboveground vegetation, living roots and dead roots. Root carbon density in degraded artificial grassland and natural grassland accounted for more than 90% of the total biomass carbon density, while the roots carbon density in black soil land accounted for 79.41%. The variation of carbon density in living roots was greater than those in aboveground vegetation and dead roots among three types of grassland, therefore, we initially considered that living roots carbon density may be a sensitive indicator of grassland degradation.