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Role of plants in wetland ecosystems

This research facilitates quantification and improved understanding of biogeochemical processes in sensitive marsh ecosystems that are being exposed to increasing nutrient inputs through human activities.

Increased nutrient inputs may lead to vegetation changes affecting ecosystem processes such as nitrogen (N) and phosphorus (P) uptake and recycling, N2-fixation, and mineralization. Research objectives designed to answer many of these questions have been a part of Dr. Rejmankova's NSF project “Linking ecosystem processes and community structure along salinity and nutrient gradients in tropical marshes”. The first phase of that project has been completed during this review period and we received additional funding for the second phase “Linking ecosystem processes and community structure in tropical marshes: the role of macrophytes and microbial communities”. We have established a field manipulative experiment to obtain a mechanistic explanation for an ecosystem level response to increased nutrient input. The central hypothesis was: The macrophyte/microphyte competition following P addition will constrain N2-fixation, which eventually will lead to N limitation. We have confirmed that P additions promote the growth of macrophytes, which rapidly reduces cyanobacterial mats and thus the autotrophic N2-fixation. The current project focuses on the role of macrophytes and microbial communities in the internal N cycling. N cycles are determined by the composition and activities of sediment microbial communities, which in turn is strongly impacted by the quantity and quality of organic carbon produced by the macrophytes. The switch from P to N limitation will depend on the extent of internal N recycling and capability of heterotrophic microflora, mainly N2-fixers, to provide enough additional N. My research now includes ever increasing microbial component and since I am not trained as a microbiologist, this part of the project is conducted in cooperation with other colleagues, namely from the cooperating University of South Bohemia, USB, and the Academy of Sciences of the Czech Republic.

We were awarded a joint international supplement to the existing NSF grant to facilitate the exchange of Czech and US researchers and students. This enabled participation of several students and colleagues from USB in the field research at the study site followed by laboratory experience at UCD.