Biological nitrogen fixation (acetylene reduction) associated with blue-green algal (cyanobacterial) communities in the Beachwood Mangrove Nature Reserve. I. The effect of environmental factors on acetylene reduction activity

Nitrogen fixation of blue-green algae (cyanobacteria) associated with Avicennia marina (Forssk.) Vierh. pneumatophores and wet and dry surface sediments was investigated in the Beachwood Mangrove Nature Reserve by means of the acetylene reduction technique. Studies revealed percentage moisture and temperature to be the prime factors influencing ARA (acetylene reduction activity) in these habitats and rates were highest under submerged conditions and at 22°C. High concentrations of inorganic nitrogen (between 1 and 5mg l−1) significantly depressed ARA in all habitats. Increases in ARA occurred with increase in light intensity up to 40 μE m−2 s−1, with negligible dark rates being recorded in association with the wet and dry surface sediments. Significant dark rates of ARA and stimulation of ARA by sucrose in association with the pneumatophores indicated that bacteria may also be contributing to ARA in this habitat. No organic carbon stimulation was noted in the other sites. Salinity had little effect on ARA over the range generally experienced in each habitat