Nitrogenase activity in tropical carbonate marine sediments

Abstract

Rates of nitrogenase acbvity were investigated in carbonate sediments of shallow tropical waters uslng the acetylene (C2H2) reduction method Nitrogenase achvlty was significantly h g h e r in fine grained sedments than m coarser grained sands The importance of oxygen, ammonium (NH:) and organic substrate availability in regulating nitrogenase activ~ty in these sedlments was evaluated The effect of O2 was vanable and appeared to be influenced by physical dsturbance of the sediment Ammonium did not appear to inhibit rates of N2 fixation over the range of in situ concentrahons observed, as there was no significant correlation of N2 fixation rates and pore water NH: Neither additions of NH: nor MSX (L-methonlne-DL-sulfoxlmine a nltrogenase derepressor) had any consistent effect on N, flxatlon N2 fixation rates were correlated w t h total organlc content of sediments Additions of mannltol and glucose led to significant, concentrahon-dependent stimulation of N2 fixahon We therefore conclude that organic substrate avallabllity is a malor factor controlling rates of nitrogenase activlty in these shallow carbonate sediments Based on our experiments benthic heterotrophic bactena in carbonate sediments could account for d d y N2 fixation lnputs of 0 07 to 5 2 mg N m-2 (0 03 to 1 9 g N m yr-l) These estimates indicate that the extensive areas of carbonate sedlments in these environments may contnbute a substant~al amount of nitrogen to shallow tropical and subtropical ecosystems

Temporal and spatial variation in nitrogen fixation activity in the eelgrass Zostera marina rhizosphere

“…9, Table 1). Repression of nitrogenase activity by NH4+ is often variable in sedi m e n t~, both with and without vegetation, and may partly reflect differences in bacterial populations that vary in their susceptibility to NH4+ inhibition , O'Neil & Capone 1989. It is possible, however, that we did not observe NH4+ repression of nitrogen fixation in either the intact cores or sediment slurries because in situ nitrogen fixation activities were already below maximum rates because of the presence of NH,+ , and thus NH,' additions would be unlikely to further decrease nitrogen fixation rates.…”

High sensitivity measurements of nitrogen isotopic ratios in coral skeletons from Palau, western Pacific: Temporal resolution and seasonal variation of nitrogen sources

“…In coral reef ecosystems, N 2 fixation is conducted by various types of organisms, including symbiotic algae in coral; sponges; mat-forming and epiphytic algae; and microalgae in sediments (Weibe et al, 1975; York (1969). Iizumi, 1992;Crossland and Barnes, 1976;Corredor et al, 1988;Miyajima et al, 2001;O'Neil and Capone, 1989;Lesser et al, 2004). Yamamuro et al (1995) also reported 15 N-depleted macrophytes (δ 15 N~0‰) in the Palau reef, supporting N 2 fixation.…”

“…In order to understand the mechanism of the high productivity, investigation of the nitrogen cycle within the coral reef ecosystem is essential, since nitrogen is one of the most important nutrients. Biogeochemical studies have suggested that one of the nitrogen sources for reef ecosystem is atmospheric nitrogen, which is assimilated by symbiotic algae in coral, sponges, mat-forming and epiphytic algae, and by microalgae in sediments (Weibe et al, 1975;Iizumi, 1992;Crossland and Barnes, 1976;Corredor et al, 1988;Yamamuro et al, 1995, Miyajima et al, 2001O'Neil andCapone, 1989, Lesser et al, Wright et al (1988) established a technique that enabled nitrogen isotopic ratios to be measured on subnanomole samples of molecular nitrogen. We have developed a similar system by using a modified noble gas mass spectrometer .…”

Budget of Primary Production and Dinitrogen Fixation in a Highly Seasonal Red Sea Coral Reef

“…Moreover, after first evidence of a diazotroph-coral association by Shashar and others (1994a) and the subsequent discovery of diazotrophic cyanobacteria in the tissue of scleractinian corals of the genus Montastraea (Lesser and others 2004), there has been emergent recognition of the potential contribution of N 2 -fixing symbioses in coral reefs (Fiore and others 2010;Cardini and others 2014). Although reef sediments and cyanobacterial mats show high rates of BNF (O'Neil and Capone 1989;Capone and others 1992;Shashar and others 1994b;CharpyRoubaud and others 2001;Bednarz and others 2015b), N 2 -fixing coral symbioses may also be responsible for significant inputs of N on the ecosystem level, particularly in reef habitats with high live coral coverage.…”