Nitrogen Fixation (Acetylene Reduction) Associated with Decaying Leaves of Pond Cypress ( Taxodium distichum var. nutans ) in a Natural and a Sewage-Enriched Cypress Dome

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Abstract
Surface litter from a natural and a sewage-enriched cypress dome in north-central Florida showed a pronounced seasonal pattern of nitrogenase (acetylene reduction) activity associated with seasonal leaf fall from deciduous trees in the domes. Samples of peat from cores indicated negligible nitrogenase activity below the surface layer. Integrating the monthly rates of nitrogen fixation (based on the theoretical molar ratio of 3:2 for C 2 H 4 /NH 3 ) yielded 0.39 and 0.12 g of N/m 2 per year fixed in the litter of the natural and sewage-enriched domes, respectively. The nitrogen fixed in the first 3 months after leaf fall in the natural dome represented about 14% of the nitrogen increment in the decomposing cypress leaves, but fixation contributed a negligible amount of nitrogen (<1%) to decomposing litter in the sewage-enriched dome.