NITROGEN FIXATION IN CAN GIO MANGROVE AND THE INVOLVING MICROORGANISMS
Abstract
Mangrove sediments are usually limited in nifrogen and phosphorous. Dissolved nittogen, the largest nittogen reservoir would help to solve this problem through activity of nittogen-fixing microorganisms, the role of these microbes is therefore quite important in mangrove ecosystem. In Cangio mangrove, the total nittogen content was measured highest at 2 - 3 cm surface of the sediment (342 nmol.kg"') and gradually decreased with depth, indicating the contribution of nittogen washed out from land to the surface layers and the role of native nittogen fixing microbes in supplying nittogen for deeper layers. By using acetylene reduction assay, the enzyme nittogenase was determined with minor activity in the surface layers, but with high activity concenttated at the depth below 5 cm, where oxygen is limited. Analyses of clone library of the nijH gene, coding for dinittogenase reductase of the nittogenase complex showed highly diversed nifrogen-fixing communities in both surface and deep sediments, among those anaerobic species such as Desulfovibrio and Geobacter were most abundant. This finding revealed a significant distinction between nittogen-fixing community in mangroves and that in rice or bean rhizosphere, where aerobic species (Rhizobium, Agrobacter ...) are dominant.