DISSERTATION RESEARCH: Effects of Nutrient Enrichment and Salinization on the Fate and Persistence of Soil Organic Matter in Tidal Freshwater Wetlands

沿海湿地是全球重要的碳汇，因为植物生长速率高，微生物有机物分解速率低。然而，这些生态系统正日益受到盐碱化、养分富集和其他人为干扰的威胁。盐碱化和养分富集可以改变植物生长和微生物分解，但它们对滨海湿地碳平衡的影响尚不确定。人为干扰引起的植物和微生物群落的变化可能导致湿地土壤净碳释放量增加，也可能导致土壤有机质碳储量增加。因此，土壤有机质库反映了植物和微生物之间的反馈，并将它们在长时间尺度上进行整合，为评估盐碱化和养分富集对湿地碳循环的累积影响提供了有用的工具。为了评估盐碱化和营养物富集对湿地碳循环的影响，将从格鲁吉亚沿海的潮汐淡水湿地收集土壤，这些湿地的盐度或营养物已被实验提高到高于自然水平。此外，通过在富营养化湿地和盐碱化湿地之间移植植被土芯，探索盐碱化与养分富集的交互作用。土壤将被培养一年，并分析以下方面的变化：1)土壤有机质的数量和组成；2)不同类型土壤有机质的微生物需求；3)微生物有机质分解速率。这项研究的结果将与以前收集的每个站点的植物和微生物过程数据相结合。本研究通过考察全球范围内影响湿地的两种最常见的人类活动：海平面上升和淡水管理导致的盐碱化，以及农业活动导致的养分径流，有助于对生态系统尺度碳循环的基本理解。了解这些干扰的影响对于保护湿地生态系统和维持其提供关键生态系统服务（如碳封存和野生动物栖息地）的能力至关重要。印第安纳大学公共与环境事务学院的环境科学与政策专业学生以及乔治亚州海岸生态系统LTER校园项目的k-12教育工作者将参与这项研究的各个方面。这项研究的影响将作为学校的一部分进行讨论。湿地生物学与调控课程。研究结果将在科学会议、同行评审的出版物上进行交流，并通过与萨佩洛岛国家河口研究保护区、大自然保护协会和佐治亚州自然资源部的持续合作，直接传达给格鲁吉亚沿海居民和资源管理者。

Coastal wetlands are a globally significant sink for carbon due to high rates of plant growth and low rates of microbial organic matter breakdown. These ecosystems, however, are increasingly threatened by salinization, nutrient enrichment and other human disturbances. Salinization and nutrient enrichment are known to alter plant growth and microbial breakdown, however there is uncertainty regarding their effect on the carbon balance of coastal wetlands. Changes in plant and microbial communities brought on by human disturbances may lead to either increased net carbon release from wetland soils or to increased storage of carbon as soil organic matter. The soil organic matter pool, therefore, reflects feedbacks between plants and microbes and integrates them over long time-scales, providing a useful tool for assessing the cumulative impacts of salinization and nutrient enrichment on the wetland carbon cycle. In order to assess the impacts of salinization and nutrient enrichment on wetland carbon cycling, soil will be collected from tidal freshwater wetlands in coastal Georgia where either salinity or nutrients have been experimentally increased above natural levels. In addition, the interactive effects of salinization and nutrient enrichment will be explored by transplanting vegetated soil cores between nutrient-enriched and salinized wetland sites. Soils will be incubated for one year and analyzed for changes in 1) quantity and composition of soil organic matter 2) microbial demand for different types of soil organic matter and 3) rates of microbial organic matter breakdown. Results from this study will be integrated with previously collected data on plant and microbial processes at each site. This research contributes to a fundamental understanding of ecosystem scale carbon cycling by examining two of the most common human activities affecting wetlands on a global scale: salinization resulting from rising sea level and freshwater management, and nutrient runoff from agricultural activities. Understanding the impacts of these disturbances is important for protecting wetland ecosystems and maintaining their ability to provide key ecosystem services, such as carbon sequestration and wildlife habitat. Environmental science and policy students from the School of Public and Environmental Affairs at Indiana University and k-12 educators from the Georgia Coastal Ecosystems LTER Schoolyard Program will be involved in all aspects of this study. The implications of this research will be discussed as part of the School?s Wetlands Biology and Regulation course. Results will be communicated in scientific meetings, peer-reviewed publications and directly to coastal Georgia residents and resource managers through ongoing collaborations with the Sapelo Island National Estuarine Research Reserve, The Nature Conservancy and the Georgia Department of Natural Resources.