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

University Of California-Davis, Davis CA

Investigators

Abstract

Abstract Proposal number 0516159: Linking ecosystem processes and community structure in tropical marshes: the role of macrophytes and microbial communities Ecosystem 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.