雅砻江下游表层土壤碳储量及其驱动因素

采集青藏高原东南缘雅砻江下游代表性植物群落表层土壤(0 ~ 10cm)样品, 测量土壤不同形态碳含量和稳定碳同位素组成(δ13Corg), 运用δ13Corg和化学计量指标探讨干热河谷土壤碳储量及其驱动因素。结果表明: 1)雅砻江下游表层土壤碳储量为121×109 kg C, 其中颗粒有机碳储量占79.48 %, 颗粒无机碳储量占20.05 %, 溶解有机碳和溶解无机碳储量甚微。2)比较发现, 研究区土壤碳含量和碳汇潜力较大。土壤有机碳(SOC)含量较高(21.23g/kg), 尤其杂木林地SOC含量高达49.71g/kg。揭示研究区物种多样性对SOC含量的贡献。研究区分布多种植物群落且具有较强的光合碳同化(植被叶片碳氮比(C/N)高达31.21)固碳能力, 为研究区较大的SOC储量提供了充足的植物源碳保障。研究区较大的土壤无机碳含量和成壤无机碳输出通量(2.065×108 kg C/a), 揭示研究区存在相当大的成壤无机碳碳汇过程和贮存潜力。在流域尺度上计算土壤成壤无机碳碳汇时, 径流输出的成壤无机碳不可忽视。3)研究区土壤C/N变化率和δ13Corg变化率空间变化均不显著(p>0.05), 揭示研究区不同群落土壤微生物代谢活动无显著差异。研究区SOC含量变化受非生物因素(气温、降水和坡度)驱动的生物因素(群落生产力和微生物代谢活动)调控。本研究可为土壤碳汇/源调控机制研究和实现我国"碳中和"目标提供基础数据。

Topsoil carbon storage and its driving factors in the lower reaches of the Yalong River

Topsoil(0 ~ 10cm) samples were collected from typical plant communities in the lower reaches of the Yalong River in the southeastern Tibetan Plateau. The contents of total carbon, total nitrogen, particulate organic carbon, dissolved organic carbon, dissolved inorganic carbon and stable carbon isotopic composition(δ13Corg) were measured. The δ13Corg and stoichiometry were employed to investigate soil carbon storage and its driving factors in hot dry valley. The results show that: (1) The topsoil carbon storage is 121×109 kg C in the lower Yalong River. Of which, particulate organic carbon storage(95×109 kg C) accounts for 79.48 %, particulate inorganic carbon storage(26×109 kg C) comprises 20.05 %. Dissolved organic carbon and dissolved inorganic carbon reserves are negligible. (2) By comparison, there are considerable soil carbon content and carbon sink potential in the study area. Higher soil organic carbon(SOC) content(21.23g/kg), especially mixed woodlands site SOC content(49.71g/kg), revealing that contribution of species diversity to SOC content in the study area. A variety of plant communities and a strong photosynthetic carbon assimilation(higher carbon nitrogen ratio(C/N, 31.21) of vegetation leaves) carbon sequestration ability provided sufficient plant source carbon guarantee for the higher SOC content in the study area. Higher soil inorganic carbon content and pedogenic inorganic carbon export fluxes(2.065×108 kg C/a), implying that there is considerable potential of carbon sink and storage of pedogenic inorganic carbon in the study area. It is suggested that the export fluxes of pedogenic inorganic carbon carried by runoff should be considered in the calculation of pedogenic inorganic carbon sink on a basin scale. (3) The gradient differences of the soil C/N ratio and δ13Corg were not significant(p>0.05), indicating that there is no significant difference in soil microbial metabolic activity among the plant communities. The SOC content was coupling controlled by abiotic factors(temperature, precipitation and slope) and biological factors(community productivity and microbial metabolic activity) in the study area. This study can provide basic data for the discussion of soil carbon sink/source regulation mechanism and the realization of Chinese "carbon neutrality" goal.