东北沼泽湿地土壤碳库分子结构特征及其稳定性对气候变化响应机制

Deciphering how molecular characteristics of soil carbon pool response to hydrothermal condition variations on micro scales is promise for elucidation of assessing stabilities of wetland soil carbon pool facing future climate change scenarios. In the present project, representative wetland types, including marsh, marshy meadow and peatland, were chosen as study areas for general filed investigation and in-situ Open Top Chambers (OTC) experiments realizing warming and precipitation adjustment. laboratory microcosm experiments are also involved, aiming to depict molecular features of wetland soil carbon pools in Northeast by Pyrolysis - gas chromatography-mass spectrometry (Py-GC/MS) technology. Biomarker and stable isotopes (δ13C、δ15N) were employed to identify stable carbon molecular and to fingerprint their sources. By means of the method of space instead of time and results from OTC experiments, we hope to differentiate the main and combined effects of hydrothermal conditions, plant cover, net primary productivity (NPP) input and litter decompositions on variations of molecular structure shifting and origins of stable carbon in wetland soil. Two ecological models, Biomod2 and LPJ, are applied to predict potential changes of wetland distribution, vegetation succession and NPP under future climate change scenarios. We finally hope to forecast and assess stability changes and spatial distribution of wetland soil carbon pools, and to provide the flexible countermeasure to avoid the adverse effects of future climate change on wetland soil carbon pool. Our results would better the current understanding of feedbacks between climate change and carbon circulation on regional scale.

从微观尺度上阐明湿地土壤碳库分子结构特征对水热条件波动的响应机制是预估未来气候变化情境下湿地土壤碳库稳定性的基础与核心问题。本项目选择东北区典型沼泽、沼泽化草甸及泥炭地，结合面上调查、室内模拟及野外原位OTC增温控水实验，利用Py-GC/MS(热裂解-气质联机)及同位素（δ13C、δ15N）等分析测试技术，分析东北典型湿地土壤碳库分子结构特征，通过生物标志物及同位素特征识别土壤稳定性碳分子结构及来源；以“空间代替时间”的方法，结合原位OTC增温控水实验结果，分析不同水热组合、植被组成、NPP输入及枯落物分解过程对土壤稳定性碳库分子结构特征及来源变化的主效应及其交互效应，识别并阐明主要影响因子及其作用机制；利用Biomod2及LPJ模型模拟未来气候变化背景下东北区湿地分布、植被演变及NPP变化，预估未来气候变化情境下东北地区湿地碳库稳定性及时空分布格局，并提出适应未来情景变化的适应性对策。

通过广泛的面上调查与实验室分析，初步明确了东北典型沼泽湿地土壤中有机碳的含量与空间分布，利用Py-GC/MS技术，明晰了东北典型沼泽湿地土壤有机碳库的分子结构特征，通过生物标志物的分析，揭示了典型湿地土壤有机质及其稳定性碳组分。利用空间代替时间的方法，结合野外原位监测，揭示了水热波动对湿地土壤碳库稳定性影响及分子转换机制；考察了利用生物炭修复东北典型湿地土壤碳库的潜力与机理。研究发现，Py-GC/MS分析获得典型湿地土壤样品中识别出400多种不同的热解产物，湿地土壤中酚类化合物占主导地位，约占总热解产物的24.11％，湿地土壤中木质素组分较为丰富，但是含氮化合物种类较少。湿地垦殖为农田后，农田土壤中的SOC、N、S及LOC含量均显著低于湿地，湿地与农田土壤中化学组分最明显的差异是在农田土壤中具有高的Alkyl-C，短链alkanes and al kenes (<C16)，同时农田土壤中的木质素较低；气候变暖的背景下，湿地旱化并导致蚂蚁入侵后，土壤的有机碳分子结构特征发生显著变化，其中最明显的为木质素组分的急剧损耗，这表明，湿地土壤中的木质素组成并不像想象中的那么稳定。湿地土壤中水分含量是调控土壤中木质素成分重要因素，气候变暖可能导致土壤中源于植物叶片的生物标志物增多。通过施加生物炭修复退化湿地土壤碳库发现，生物炭添加量的增加显著降低了土壤有机碳中多糖（Ps）的含量，但对溶解性有机碳分子结构影响很小。