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，因为植物生长速度快，微生物有机物质分解率低。然而，这些生态系统日益受到盐碱化、营养丰富和其他人类干扰的威胁。众所周知，盐碱化和营养丰富可以改变植物生长和微生物分解，但它们对沿海湿地碳平衡的影响尚不确定。人类干扰引起的植物群落和微生物群落的变化可能导致湿地土壤净碳释放增加，或增加土壤有机质碳的储存。因此，土壤有机质库反映了植物和微生物之间的反馈，并在长时间尺度上整合它们，为评估盐碱化和养分丰富对湿地碳循环的累积影响提供了有用的工具。为了评估盐碱化和养分富集化对湿地碳循环的影响，将从佐治亚州沿海的潮汐淡水湿地收集土壤，这些湿地的盐分或养分已经实验增加到高于自然水平。此外，还将通过在营养丰富的湿地和盐碱化的湿地之间移植植被土芯来探索盐碱化和营养丰富的互动效应。土壤将培养一年，并分析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和3)微生物有机质分解率的变化。这项研究的结果将与之前收集的关于每个地点的植物和微生物过程的数据相结合。这项研究通过考察在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，以及农业活动的养分径流，有助于从根本上理解生态系统规模的碳循环。了解这些干扰的影响对于保护湿地生态系统和保持其提供碳固存和野生动物栖息地等关键生态系统服务的能力非常重要。印第安纳大学公共与环境事务学院的环境科学和政策专业的学生以及佐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所有方面。这项研究的意义将作为S湿地生物学与调节课程的一部分进行讨论。结果将通过与萨佩洛岛国家河口研究保护区、自然保护协会和佐治亚州自然资源部的持续合作，在科学会议、同行评议出版物中传达，并直接传达给格鲁吉亚沿海居民和资源管理人员。

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.