半干旱区不同类型生态系统土壤有机碳分解速率对干湿交替响应及其机制

Drying-rewetting event is one of the most important environmental factors that regulate the ecosystem carbon cycling in semi-arid regions. Therefore, we will investigate the short-term and long-term effects of soil drying-rewetting cycles on decomposition of soil organic matter , and their potential mechanisms related to soil organic carbon pool composition and soil microbial community structure in the natural and lab conditions. During modeling experiment,we will collect the mineral soil samples under typical degraded sandy grassland and Mongolian pine (Pinus sylvestris var. mongolica) plantation in the Keerqin sandy land, China. Then, we will incubate the soils in an laboratory conditions with the repeated drying and rewetting cycles. In this project, we will investigate: (1) the responses of soil organic carbon mineralization rates to the drying-rewetting event during short-term and long-term time scale; (2) the effects of drying-rewetting event on the decomposition rates of soil organic carbon pools with the different turnover time， based on soil density fraction method; (3) the effects of drying-rewetting event on the composition and transformation of soil organic carbon pools; (4) the changes of soil microbial biomass C and N, and soil microbial community structure. The main objects of this project are to examine the influencs of soil drying-rewetting event on the decomposition rates of soil organic carbon and the long-term stability of soil organic carbon under the different tpyes of terrestrial ecosystems in semi-arid regions. Further, we will study the mechanisms of the changes in soil organic carbon pool composition, and soil microbial biomass and community structure induced by drying-rewetting event.

土壤干湿交替是影响半干旱地区陆地生态系统碳循环过程的最重要自然环境因子之一。因此，本项目以我国北方科尔沁沙地典型的退化沙质草地和沙地樟子松人工林为研究对象，采用野外观测与室内模拟控制试验方法，开展干湿交替环境对半干旱地区不同类型生态系统土壤有机碳分解速率短期和长期的潜在影响及其机制研究。研究内容主要包括：（1）土壤有机碳分解速率对反复干湿交替环境的短期和长期响应；（2）土壤不同活性有机碳分解速率对干湿交替环境响应的异质性；（3）干湿交替对土壤有机碳库组成和迁移过程影响；（4）干湿交替对土壤微生物量和群落结构组成影响。通过上述研究，探讨半干旱地区不同类型生态系统土壤有机碳分解速率和土壤有机碳长期稳定性对干湿交替环境的响应，进而揭示其相关的土壤有机碳组成和土壤微生物学机制。

土壤干湿交替是影响半干旱地区陆地生态系统碳循环过程的最重要自然环境因子之一。因此，本项目以我国北方科尔沁沙地典型退化沙质草地和沙地人工林为研究对象，采用室内和模拟控制试验方法，开展干湿交替对半干旱地区不同类型生态系统土壤有机碳分解过程影响及微生物机制研究。本项目主要开展以下几个方面研究：（1）模拟干湿交替变化对沙地樟子松和杨树人工林凋落物分解速率和养分释放影响;（2）自然和室内模拟干湿交替变化下草地和沙地森林土壤呼吸速率动态;（3）干湿交替变化对土壤有机碳结构和储量影响;（4）干旱和干湿交替变化对土壤微生物量和群落组成影响。研究结果发现:（1）干湿交替、树种和培养时间均能够影响叶凋落物质量残留率，而不同干湿交替强度对叶凋落物N和P养分释放速率影响不显著;（2）随着土壤逐渐干燥，土壤呼吸CO2释放速率逐渐降低，当干燥土壤再湿润时，土壤呼吸速率能够迅速恢复到湿润处理水平，干湿交替循环过程中干旱时间增加能够减少土壤呼吸累积释放CO2量，同样在自然降水量减少情景下沙地樟子松人工林土壤呼吸释放CO2速率下降8.1~13.9%，而草地土壤呼吸速率差异不显著;（3）干湿交替影响土壤团聚体结构组成，干湿交替频率增加有利于>0.25 mm土壤团聚体有机碳库储量的增加;（4）自然降水量减少对土壤微生物群落结构组成影响不显著，而土壤干湿交替变化强度和频率能够影响土壤微生物群落结构，表明相比于降水量变化，未来极端干旱或降水事件可能对土壤微生物群落影响更加重要。本项目研究，有助于更好了解半干旱地区不同类型生态系统对未来降水格局变化的响应。