外源碳输入对三江平原沼泽湿地土壤有机质分解的影响

The decomposition of soil organic matter (SOM) plays a significant role in terrestrial carbon cycle and has a direct effect on the atmospheric greenhouse gases concentration and global warming. Wetland ecosystems, as an important organic carbon pool with the low temperature and anaerobic conditions inhibit the decomposition of SOM, leading to a large amount accumulation of organic carbon in soils, and its sensitivity to global climate change and feedback effects can’t be ignored. Climatic warming may change the plant productivity and litter mass, and hence the amount of labile organic carbon inputs to ecosystems and induce the priming effects, which can be defined as the short-term changes in the turnover of native SOM caused by the addition of external organic matter. This may produce a marked effect on soil organic carbon decomposition and thus the carbon flux and stability of carbon pool and change the function of terrestrial carbon sink/source, which can produce a feedback on climate warming. However, the effects of global warming induced altered exogenous carbon input of ecosystem on SOM decomposition are still uncertain and some related researches are still needed. In the context of global warming and precipitation pattern change, this project takes the typical seasonal inundated wetland ecosystems in the Sanjiang Plain of Northeast China as the study object, through field observation and incubation experiment to: (1) reveal the effects of exogenous carbon input on the fluxes of CH4 and CO2 in wetland ecosystems, (2) illuminate the effects of exogenous carbon amendment on SOM decomposition and the intensity and direction of priming effect, (3) clarify the influence of different microbial groups on CH4 and CO2 emissions and soil priming effects in wetland. In conclusion, the final objectives of this project are to provide scientific basis for the better prediction of soil carbon cycling, soil carbon pool functions and its response and feedback on global climate change in wetland ecosystems of northeastern China.

土壤有机质分解是陆地生态系统碳循环的重要组成部分，直接影响大气中温室气体浓度，对全球变暖产生反馈效应。湿地生态系统是陆地重要有机碳库，低温、厌氧条件抑制了有机质分解，导致大量有机碳积累，对全球气候变化的敏感性与反馈作用不容忽视。气候变暖导致植被生产力和凋落物量增加，影响生态系统活性碳输入，发生激发效应作用于土壤有机质的分解过程，影响生态系统碳排放、碳库稳定性和陆地碳汇/源的功能，对气候变暖起到反馈效应。然而，相关研究仍存在着一定的不足与不确定性。本项目以三江平原季节性积水沼泽湿地为研究对象，通过野外定位观测和室内培养实验结合的方法，明确外源碳输入对沼泽湿地CH4、CO2排放的影响，阐明外源碳添加对湿地土壤有机质分解激发效应强度及作用方向，并从微生物群落结构特征探究其影响机制，为我国北方沼泽湿地生态系统碳循环过程、湿地土壤碳汇功能变化预测及其对全球气候变暖的响应与反馈效应研究提供科学依据。

植物凋落物，包括立枯物调控对湿地生态系统碳循环及其平衡过程有显著影响，而凋落物质、量的变化受全球环境变化的影响。有关植物凋落物在生态系统呼吸过程的基本功能、作用研究，对于大气-陆地生态系统间的碳交换评价研究至关重要。然而，到目前为止，湿地植被凋落物调控对湿地生态系统呼吸碳排放及其温度敏感性有何影响仍不清楚。在本实验中，我们在位于东北三江平原的典型季节性积水沼泽湿地中布置野外原位定位长期控制观测实验，通过对来源于湿地植被的凋落物进行人工调控，添加或是去除现存凋落物，以研究湿地植物凋落物在湿地生态系统呼吸中的作用，并探讨相关作用机制。我们的研究发现，湿地生态系统呼吸CO2排放受到凋落物调控的显著影响，凋落物添加后可以增加湿地CO2排放，而凋落物去除后可以降低湿地CO2排放，本研究中这种处理效应在第二年的作用效果要优于第一年，并且CO2排放变化要更受凋落物去除处理的影响。采集不同凋落物输入处理下呼吸作用气体样品的同时，定期对土壤孔隙水样品进行了收集，发现不同凋落物输入处理下孔隙水中可溶性有机碳（DOC）和无机氮（NH4+）有显著差异，说明湿地植被凋落物作用下生态系统有不同的碳氮来源；同时，DOC和NH4+作为微生物可以直接利用的碳源、氮源，二者的变化也将显著作用于生态系统碳循环过程。不同凋落物输入处理下生态系统呼吸CO2排放温度敏感性Q10值发生了一定变化，受凋落物输入的影响：所有凋落物（包括立枯物及地表凋落物）去除处理下Q10值最高，表现出湿地土壤在全球变暖背景下受到干扰下更倾向于碳排放过程。我们的研究结果也表明，在有湿地植被覆盖条件下，深层土壤（15cm以下）CO2排放温度敏感性变化Q10值要低于凋落物去除处理，也表现出湿地植被在湿地生态系统固碳中的重要作用。总体来说，我们的研究结果表明在全球环境变化影响下，在预测生物圈-大气圈碳交换时要考虑到湿地植被凋落物输入到土壤系统中变化情况的重要性。