Linking Ecosystem Processes and Community Structure in Tropical Marshes: The Role of Macrophytes and Microbial Communities

摘要提案号0516159：链接热带沼泽生态系统过程和群落结构：大型植物和微生物群落的作用热带生态系统变化迅速增加，但热带湿地生态系统对养分输入大规模变化的反应尚不清楚。本研究的目的是获得生态系统水平对沿盐度梯度增加的养分输入的响应的解释。一项从2001年开始的长期实验将继续进行，其中包括向一组复制的沼泽添加营养物质。这些地块的一个子集将用于更详细地检查碳、氮和磷循环的特定组成部分。将利用根系微观模型对根系分泌物进行详细评估，并利用分子方法对沉积物细菌群落进行研究。到目前为止，我们证实了磷的添加促进了大型植物的生长，导致蓝藻席的减少和固氮的消除。在此基础上，我们建议继续在田间试验中对响应变量进行常规监测，并重点研究大型植物和微生物群落在磷氮内部循环中的作用。我们假设这种循环是由沉积物微生物群的组成和活动决定的，而这些微生物群又受到自养生物（大型植物和蓝藻垫）产生的有机碳的数量和质量的强烈影响。外加磷显著改变了自养群落，从而改变了有机质的输入量。不同的大型植物（香蒲和灯芯草）由于其产生的有机物质的质量和数量不同，对微生物群落的影响也不同。从磷限制到氮限制的转变将取决于内部氮循环的程度和异养微生物群提供足够额外氮的能力。这项研究将有助于量化和提高对人类活动导致的营养投入增加的敏感沼泽生态系统的结构变化和生物地球化学过程的理解。它在伯利兹和其他热带地区的生物保护和疾病控制方面具有重要的管理应用。

AbstractProposal number 0516159: Linking ecosystem processes and community structure in tropical marshes: the role of macrophytes and microbial communitiesEcosystem alterations in the tropics are increasing rapidly yet reactions of tropical wetland ecosystems to large-scale changes of nutrient input are poorly understood. The aim of this research is to obtain an explanation for an ecosystem level response to increased nutrient input along a salinity gradient. A long-term experiment, involving additions of nutrients to a replicated set of marshes that have started in 2001, will continue. A subset of the plots will be used for more detailed examination of specific components of carbon, nitrogen and phosphorus cycling. Root microcosms will be employed for detailed root exudates assessment and molecular methods will be utilized to investigate the sediment bacterial communities. So far, we confirmed that phosphorus additions promote the growth of macrophytes leading to reduction of cyanobacterial mats and elimination of nitrogen fixation. Building on these results, we propose to continue with the routine monitoring of response variables in the field experiment and, in addition, concentrate on the role of macrophytes and microbial communities in the internal phosphorus and nitrogen cycling. We hypothesize that this cycling is determined by composition and activities of sediment microflora, which in turn is strongly impacted by the quantity and quality of organic carbon produced by the autotrophs (macrophytes and cyanobacterial mats). External addition of P dramatically changes the autotroph community thus changing the quantity of the input of organic materials. Different macrophytes (cattails vs. rushes) will have different impact on microbial community due the differences in the quality and quantity of organic material they produce. The switch from phosphorus to nitrogen limitation will depend on the extent of internal nitrogen recycling and capability of heterotrophic microflora to provide enough additional nitrogen. This research will facilitate quantification and improved understanding of the changing structure and biogeochemical processes in sensitive marsh ecosystems exposed to increasing nutrient inputs through human activities. It has important management applications for biological conservation and disease control in Belize and other tropical regions.