Correlation between diversity of nitrogen-fixing bacterial community inhabiting the rhizoplane of acid sulfate soil-tolerant local paddy plant and rice production

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In this study, we revealed a potent ability of Kalimantan local rice varieties cultivated on acid sulfate soil paddocks in South Kalimantan, Indonesia, and this rice production is regarded as a representative highly produced low-input sustainable agriculture. From the rhizoplane of local rice varieties, we have often isolated Sphingomonas spp. and a major strain was the same with those isolated from Melastoma malabathricum rhizoplane and Xyris complanata rhizosphere in South and Central Kalimantans. Thus, many Sphingomonas spp. isolated from the local rice varieties were considered to be functional rhizobacteria, 1) contributing to moderation of the rhizospherous environments, 2) directly fixing nitrogen or, at least, adjust the rhizoplane condition to be more suitable for nitrogen fixation, and 3) playing an important role in rhizo-biocomplex formation due to acceleration of microbial biomass accumulation. Therefore, rhizospherous microfloral communities including the Sphingomonas sp. established along the root system of local rice varieties are able to acquire nitrogen and buffer the rhizospherous environments, of which potent abilities are coming from their genetic diversity and stability. Since aerenchyma of the local paddy rice are remarkably developed well in the stems and roots, it is further necessary to study relationship between the inner tissue structures and endophytic nitrogen fixation.