滨海盐沼湿地多组分碳过程与净收支的复杂水文调控机制

The natural wetland ecosystems of tidal salt marshes, with large storage quantities of carbon, are defined as the “Blue Carbon Sink”. It was hypothesized that the complicated hydrological environment (e.g., tidal current, salinity and sediment deposition) at estuaries and coasts might be the key factors regulating the multiple-component processes of carbon budget (uptake, emission and turnover). However, the effect mechanism is still not clear. The natural properties of salt marsh vegetation, hydrological conditions and mudflat accretion, make the Yangtze Estuary an ideal area for the related studies. To simulate the hydrological conditions of inundation scenarios, salinity gradient and sediment concentration in the estuarine mudflat, a group of experiments will be conducted in terms of tidal-creek trestle cultivation and in-vitro controlling cultivation with the mesocosms (typical vegetation-soil monoliths) from the salt marsh wetlands. . This project will integrate the multi-objective techniques of biogeochemical research, including the measurements of CO2 and CH4 emission, C3- and C4-type photosynthesis and respiration of vegetation, carbon accumulation in biomass, assimilated carbon allocation, litter organic carbon decomposition and net export of soil dissolved carbon. Besides, the carbon processes of recently photosynthesized carbon allocation, CO2 and CH4 effluxes, carbon utilization by soil microorganisms, litter composition and soil dissolved carbon run-off will be traced based on the technique of 13C stable isotope pulse-labeling. . The aims of this study are (1) to investigate the capacities of component carbon flux and the interaction of each processes of the vegetation-soil mesocosms under complex hydrological conditions in estuarine area, (2) to fitting the nonlinear relationship between complex hydrological factors and the vertical (land-atmosphere orientation) and horizontal (water-land orientation) carbon processes, and (3) to analyze effect characteristics and regulating mechanism of hydrological factors on the net carbon budget processes in salt marsh wetland. The key scientific questions needed to be considered are (1) which carbon process components in the salt marsh vegetation-soil systems are sensitive to the environmental variables? and (2) how the hydrological processes regulate the carbon "source" and "sink" switchover in the wetland in the Yangtze Estuary? Through the study planning, the research team purposes to explore the fundamental base in terms of carbon sequestration in salt marsh in response to expected sea-level rise under climate change, as well as the carbon cycle modeling in estuarine and coastal wetlands.

滨海盐沼湿地被誉为蓝色碳汇，而复杂的水文环境（潮汐、盐度和泥沙沉积等）可能是湿地多组分碳过程（吸收、分配、排放和周转）与净收支的主控因素。本研究以长江口滨海湿地为对象，通过典型植被－土壤中型系统的野外支架培养与离体条件控制培养，建立不同潮位带淹水、盐度和泥沙含量梯度的多重对比实验。以系统CO2和CH4排放、C3与C4植物碳同化与分配、生物量碳累积、凋落物有机碳分解和溶解态碳输出的定量观测为主线，并集成13C富集标记技术示踪碳组分过程以及近期光合碳与土壤老碳的贡献率，从而1）辨析复杂水文环境下盐沼湿地系统碳过程组分分量及其之间的周转特征；2）建立多重水文因子与系统纵、横向碳过程之间的非线性关系；3）综合分析水文干扰对系统净碳收支的调控机制。拟解决的关键问题为复杂水文环境下盐沼湿地碳"汇/源"过程之间如何转换？本研究可为盐沼湿地碳过程模型的构建以及评估海平面上升对湿地碳库稳定性的影响提供依据。

滨海湿地复杂的水文环境（潮汐、盐度和泥沙沉积等）可能是多组分碳过程的主控因素。以长江口滨海湿地为对象，研究了海平面上升、盐水入侵和来沙减少对滨海湿地盐沼格局和初级生产力的影响；植被初级生产力时空格局与水盐因子的调控特征；水盐条件变化对植物光合固碳、系统甲烷通量和土壤微生物群落的影响；植被、外源沉积物和潮汐动态对土壤碳储量和潮沟碳输运的影响；植被修复后的碳汇功能提升效益。主要成果在于，（1）辨识了滨海湿地植被类群对水-沙-盐环境压力的适应性（耐受阈值），自主开发了长江口盐沼模型（SMM-YE），预测分析了海平面上升、来沙减少和盐水入侵对滨海湿地群落格局及初级生产力的影响。（2）提出了基于繁殖体-泥沙沉积-水动力“力量平衡”的潮间带植被建群新理论。在潮水动力和拥挤效应的双重影响下，植物趋向于将光合作用固定的碳更多地分配于地下部分，形成了适应潮滩环境压力的有效策略。（3）提出滨海湿地CH4通量主要受气温、潮位和光合有效辐射的控制，甲烷排放热点占到30%的日甲烷排放量，潮汐活动是甲烷通量的重要影响因子。（4）滨海盐沼土壤碳库的形成在发育早期以泥沙输入为主，植被定植后则以其碳输入为主。表层土壤碳储量受植被类型和外源沉积物空间特征的交互作用影响。滨海湿地植被群落、潮汐类型以及泥沙沉积动态对潮沟系统碳组分（DOC、DIC、POC和PIC）输运起到协同影响的作用。（5）滨海湿地植物碳储量对淹水频率变化的响应差异均不显著，盐度对植被碳储量有显著抑制作用，水盐变化对于不同植被类型的土壤微生物生物量碳和土壤酶活性也有显著影响。互花米草潮滩土壤微生物体现出较高的适应性。（6）基于我国海岸带特有种海三棱藨草的生态恢复实验，发现温和淤涨型细沙质潮滩恢复区土壤有机碳储量提高了1.14−1.52倍。地下生物量与土壤有机碳和营养物质之间存在显著相关性。植物修复初期的成功对于土壤有机碳积累起着至关重要的作用。为滨海湿地应对海平面上升的碳库管理提供了实践依据。