Seasonal changes in periphyton nitrogen fixation in a protected tropical wetland |
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Authors: | Rodrigo Vargas Eberto Novelo |
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Affiliation: | (1) Center for Conservation Biology, University of California-Riverside, University Laboratory Building, Room 207, University of California, Riverside, CA 92521, USA;(2) Departamento de Biología Comparada, Facultad de Ciencias, Universidad Nacional Autónoma de México, México, México |
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Abstract: | Cyanobacteria are important for global nitrogen cycle and often form complex associations referred to as cyanobacterial mats or periphyton that are common in tropical, limestone-based wetlands. The objective of this study was to monitor the nitrogen fixation rate using the acetylene reduction assay of these cyanobacterial mats in a tropical, unfertilized, and protected wetland. To account for temporal and spatial variation of nitrogenase activity, we were interested in seasons in a hydrological cycle (dry, rains, and end of rains), sites with different vascular vegetation, and rates of nitrogenase activity in a 24-h cycle. The annual average of nitrogenase activity was 22 nmol C2H4 cm−2 h−1, with a range of <6 to 35 nmol C2H4 cm−2 h−1, and the annual nitrogen fixation rate of our study site (9.0 g N m−2 year−1) is higher than similar estimates from other freshwater wetlands. There was a clear temporal pattern in nitrogenase activity with a maximum rate occurring during the rainy season (August) and a maximum nitrogenase activity occurring between 0600 and 1200 hours. We found spatial differences in nitrogenase activity among the four sites that could be attributed to variations in species composition within the periphyton. |
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Keywords: | Tropical wetland Periphyton Nitrogen fixation Acetylene reduction assay Cyanobacteria Mexico |
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