青海湖流域矮嵩草草甸土壤有机碳密度分布特征

通过对青海湖流域不同退化程度矮嵩草草甸土壤容重和有机碳含量的测定,确定了其土壤有机碳密度。结果表明:不同退化程度下矮嵩草草甸土壤有机碳含量和变化特征各有不同。从未退化-重度退化,0—100 cm土壤剖面平均有机碳含量分别为(25.17±4.73)g/kg,(17.51±3.06)g/kg,(20.79±1.30)g/kg和(14.53±1.20)g/kg,即未退化中度退化轻度退化重度退化;0—20 cm土壤平均有机碳含量从(64.47±11.70)g/kg减少为(14.52±1.52)g/kg,减少了77.48%。土壤剖面有机碳密度变化趋势与其有机碳含量变化趋势一致。0—100 cm土壤剖面有机碳密度分别为(18.16±4.12)kg/m3,(14.24±3.52)kg/m3,(18.64±2.82)kg/m3和(13.27±2.28)kg/m3,即中度退化未退化轻度退化重度退化;土壤有机碳集中分布在0—40 cm深度,从未退化到严重退化,该深度有机碳密度分别为(32.06±6.41)kg/m3,(25.10±4.20)kg/m3,(22.68±3.17)kg/m3和(17.10±2.77)kg/m3,比整个剖面有机碳密度高出76.53%,76.25%,21.68%和28.88%。不考虑其他因素,以空间尺度代替时间尺度,这一结果说明矮嵩草草甸的退化导致土壤逐渐释放有机碳,其作为储存碳的功能在减弱,必须加强对矮嵩草草甸生态系统的保护,以防止其碳库变为碳源。

Characteristics of soil carbon density distribution of the Kobresia humilis meadow in the Qinghai Lake basin

Soil is the largest carbon stock in the terrestrial ecosystem, storing about two-thirds of organic carbon in the terrestrial biosphere. Our understanding on the dynamic change of soil organic carbon belongs to one one of the important issue in terrestrial carbon cycle. Kobrecia humilis meadow is one major grassland type on the Qinghai-Tibetan Plateau, which has the high organic matter in soil. Under the dual effects of natural and human activities, there had great influence on the carbon balance alpine because the Kobrecia humilis meadows appeared different degree of degradation. To provide basic data and theoretical reference on accurate assessments of the Qinghai-Tibetan Plateau alpine meadow ecosystem carbon source/sink effect, this paper determined the soil organic density through measuring the soil bulk density and organic carbon content under different degrading Kobresia humilis meadow in the Qinghai Lake basin. Our results showed that there existed discrepant in the soil organic carbon content and variable characteristics under different degrading Kobresia humilis meadow. The average organic carbon content in the 0-100 cm soil profiles respectively was estimated at (25.17±4.73) g/kg,(17.51±3.06) g/kg,(20.79±1.30) g/kg and (14.53±1.20) g/kg from no degrading to heavy degraded Kobresia humilis meadow. That is, no degradation>moderate one >slight one >heavy one. Moreover, the mean of organic carbon content in 0-20 cm soil profiles from no degrading to heavy degraded reduced from (64.47±11.70) g/kg to (14.52±1.52) g/kg, and fallen by 77.48%. Variations of the soil organic carbon density in the different degrading Kobresia humilis meadow soil profiles had the same trends of soil organic carbon content. From no degrading to heavy degraded Kobresia humilis meadow, the total organic carbon density in the 0-100 cm soil profiles respectively amounted to (18.16±4.12) kg/m³, (14.24±3.52) kg/m³, (18.64±2.82) kg/m³, and (13.27±2.28) kg/m³, respectively. That is, moderate degradation> no one >slight one >heavy one. Soil organic carbon content mainly concentrated in the 0-40 cm depth. The 0-40 cm soil organic carbon density respectively was (32.06±6.41) kg/m³,(25.10±4.20) kg/m³, (22.68±3.17) kg/m³, (17.10±2.77) kg/m³, higher than 76.53%, 76.25%, 21.68% and 28.88% in 0-100 cm soil total organic carbon density. If we do not think other factors, those results indicated that the degradation of the Kobresia humilis meadow caused that soil gradually released the organic carbon and weakened the store carbon function. Especially, surface soil was more prone to release CO₂ to the atmosphere due to the continuous climatic warming. Moreover, soil organic densities in Kobresia humilis meadow were evidently higher than the mean of alpine grassland and meadow in the Qinghai-Tibetan Plateau and in the Qinghai Province and across the China, highlighting that we could not neglect it in evaluation soil organic stock across the whole Qinghai-Tibet plateau.