逆向演替与冻融作用耦合对高寒草地土壤有机碳的影响机制研究

Alpine grassland in the Yellow River,Yangtze River and Lancangjiang River,Qinghai Province,China ecological environment is fragile, sensitive to climate change and ecological function is important.Alpine grassland soil organic carbon in ecosystem carbon stability plays an important role. Due to the climate warming in certainly time scales,alpine grassland permafrost freezing and thawing pattern change with reverse succession synergistic effect aggravate the ecological problems coming from grassland deterioration. The coupling Interaction with freeze-thaw action make vegetation and soil ecological function weakened, the alpine meadow soil organic carbon pool change, soil carbon sink towards carbon source transform, increase greenhouse gas emissions,reaction to global climate change and form the bad circulation.Therefore,in this study,alpine grasslands in source area of three major rivers of China were selected as research area because they have certain research foundation.Through in-situ observation and indoor analysis to study alpine meadow soil freezing and thawing pattern under retrogressive succession sequence, and mechanism study of the coupling interaction between regressive succession and freeze-thaw action to alpine grassland soil organic carbon, and then has a certain meaning of scientific exploration to alpine meadow soil organic carbon reserves and stability mechanism research. Aim to answer the soil freezing and thawing pattern change trend and spatial heterogeneity under retrogressive succession sequence, and answer the action mechanism of the coupling interaction between regressive succession and freeze-thaw action to alpine grassland soil organic carbon distribution, organic carbon fraction form, organic carbon source, organic carbon migration and turnover, and answer the scientific problems of alpine grassland carbon pool stability maintaining mechanism.

三江源高寒草地生态环境脆弱，对全球气候变化敏感，生态地位重要，高寒草地土壤有机碳在生态系统碳稳定性中发挥着重要作用。在气候趋暖背景下，高寒草地多年冻土退化，冻融作用改变。同时，高寒草地在自然与人为因素共同扰动下广泛存在逆向演替，与冻融作用耦合，导致草地植被及土壤的生态功能削弱，草地土壤有机碳库变化，土壤碳汇向碳源转变，增加温室气体排放，形成不良循环。因此，在具备一定研究基础的三江源高寒草地通过原位观测、室内分析，开展高寒草地逆向演替序列下土壤冻融异质性研究，逆向演替与冻融作用耦合对草地土壤有机碳作用机制研究，进而对高寒草地土壤有机碳库和稳定性机制研究具有一定科学探索意义。目的在于回答逆向演替序列下土壤冻融作用变化趋势及空间异质性，逆向演替与冻融作用耦合对高寒草地土壤有机碳分布、有机碳组分构成、有机碳来源、有机碳迁移和周转等的作用机制，高寒草地碳库稳定性维持机制等科学问题。

高寒草地在全球气候趋暖背景下，土壤冻融格局改变与草地逆向演替耦合，对土壤有机碳等产生影响。通过对逆向演替不同阶段草地原位观测、冻融处理及分析测定，以揭示土壤冻融特征、土壤有机碳含量与分布、有机碳碳库稳定性等的响应机理。研究发现，高寒草甸、高寒草原研究区气温10a变化率为0.42℃、0.48℃，相对湿度10a变化率-0.95%、-1.48%，暖干化明显，是土壤冻融格局改变、植物群落演替等的驱动因子；一个冻融周期内，高寒草甸、高寒草原土壤冻结至消融历时179-196d、207-226d，重度退化较未退化各土层冻结起始日期提前7-23d、7-12d，消融起始日期提前18-38d、16-26d；未退化到重度退化，土温对气温的响应增强（r=0.646-0.951）；高寒草甸、高寒草原各退化样地0-10cm土层冻融日循环13-23d、15-27d；土壤含水量消融阶段较高，冻结阶段急剧减少，冻融交替期变化剧烈；高寒草甸、高寒草原0-30cm土层各退化程度下土壤有机碳含量31.8-63.3g/kg、8.3-25.7g/kg，有机碳储量10.2-13.3kg/m2、2.4-9.2kg/m2。退化草地随冻结时间的延长、冻融循环次数的增多土壤有机碳含量分别增加1.0%-6.0%、减少3.8%-37.3%，土壤活性有机碳含量总体增加，土壤酶活性总体降低，小粒级团聚体有机碳含量增加、大粒级团聚体有机碳含量减少；退化草地土壤有机碳碳库指数随冻结时间的延长增大，随冻融循环次数的增多降低；土壤碳库管理指数高寒草甸、高寒草原各退化程度下为23.5%-70.2%、39.0%-71.9%，随退化加剧显著降低，并随冻结时间的延长增加0.3%-13.4%、4.4%-8.2%，随冻融循环次数的增多降低3.8%-4.1%、1.0%-2.7%，与草地逆向演替及冻融作用相关（r>0.900）；植被盖度、生物量、冻融循环次数、冻结时间是影响土壤有机碳含量、碳库稳定性和草地土壤质量的重要因素。逆向演替与冻融作用耦合下，高寒草地土壤有机碳储量减少，不利于有机碳碳库稳定性及碳汇，增大了高寒草地碳排放压力。