辽河口湿地土壤碳排放对水盐条件的响应及其机制

Estuary wetlands are located where rivers flow into the sea and the carbon gas emissions from soil are seriously controlled by water and salinity because of the tidal effects. However, it’s still unclear how patterns and what mechanisms the carbon gas emission responses to the comprehensive effects of water and salinity. In order to study the responses of the carbon gas emissions from soil to water and salinity and its mechanisms, a water-salinity gradient zone is to be selected in Liaohe estuarine wetland, and the methods of an in situ observation in field combined a microcosm incubation in laboratory are to be used. Our aims are 1) to study the soil respirations and CH4 emissions from soil along the water-salinity gradient and reveal the key factors influencing the carbon gas emissions, 2) to study the patterns of carbon gas emission and carbon aerobic/anaerobic mineralization responding to water and salinity in the microcosm incubation, 3) to study the effects of water and salinity on the characteristics of soil redox reaction, ionic strength and type, matrix quality, microbial activity and microbial community structure in incubations, 4) to analysis the correlations between carbon gas emission and soil chemical and microbial qualities, and 5) to discuss the mechanisms of carbon gas emission responding to the water and salinity effects. The expected results of the research could contribute to understand the carbon turnover in estuary wetland and provide the data to evaluate the influence of seawater intrusion on carbon loss in northern estuary wetlands.

河口湿地位于河流入海处，受潮汐作用的影响，土壤碳排放动态严重受制于水盐环境的变化，但河口湿地碳排放过程对水盐综合作用的响应规律及其机制尚不明确。本申请项目拟通过野外样区定位观测，研究辽河口湿地不同水盐梯度上土壤CO2与CH4排放的时空动态特征，揭示不同水盐梯度上湿地土壤碳排放的关键影响因子；通过室内模拟培养，研究不同水盐处理下土壤CO2与CH4排放动态与碳矿化过程，明确湿地土壤碳排放过程对水盐条件的响应规律；通过分析土壤碳排放与土壤氧化还原条件、离子强度与类型、可利用底质的性质、微生物活性与群落结构的关系，揭示土壤碳排放响应水盐条件的关键生物与化学机制。本研究将有助于揭示河口湿地碳过程机理，并为评估海水入侵对北方河口湿地碳损失的影响提供科学依据。

河口湿地位于河流入海处，受潮汐作用的影响，土壤碳排放严重受制于水盐环境的变化。为探明河口湿地碳排放对水盐变化的响应及其相关机制，本项目执行期间，基于野外观测与室内模拟培养等试验方法，重点开展了辽河口湿地不同水盐梯度上碳排放的时空变化特征、碳排放对水盐条件的响应规律、碳排放响应水盐条件的生物与化学机制等研究内容。研究发现：（1）6~11月，辽河口芦苇湿地、翅碱蓬地和裸滩三种类型湿地CO2与CH4随季节呈现出不同的排放特征，微咸水湿地排放速率高于咸水湿地，盐度和植物生物量是关键控制因素，潮汐降低了CO2与CH4的排放；（2）水盐变化对河口湿地CO2和CH4排放产生了显著影响。盐分升高降低了CO2和CH4排放速率，这主要与水盐变化改变了土壤理化性质特别是电导率（EC）、pH和微生物量碳（MBC）有关：淹水条件下（+5cm），CO2和CH4排放与EC和pH显著相关；波动水位下（-5cm~+5cm），CO2和CH4排放与EC和MBC显著相关。（3）盐水入侵提高了土壤离子强度，降低了基质的有效性，改变了土壤微生物群落结构，并最终导致土壤呼吸速率的下降；在3‰~5‰之间存在一个控制土壤呼吸的盐度阈值，在该阈值内即使较小的盐度变化也可能触发对基质有效性和微生物群落结构的抑制效应；盐分对河口湿地有机碳有氧/厌氧矿化的作用因离子类型而异，Cl-的作用强度强于SO42-，且中低浓度SO42-（<10‰）对碳矿化具有促进作用。本项研究阐明了河口湿地碳排放过程对水盐变化的响应规律，并从盐离子强度、盐离子类型、基质有效性和微生物群落结构等角度，揭示了河口湿地碳排放响应水盐变化的生物化学机制。本项目执行期间，发表论文10篇，其中Top期刊论文3篇，CSCD 7篇；培养研究生5人。相关研究成果为揭示河口湿地碳排放对海水入侵的响应机制提供了科学依据，为评估全球变化背景下河口湿地碳损益提供了科学参考。