Molecular Analyses of the Distribution and Function of Diazotrophic Rhizobia and Methanotrophs in the Tissues and Rhizosphere of Non-Leguminous Plants

Abstract

Biological nitrogen fixation (BNF) by plants and its bacterial associations represent an important natural system for capturing atmospheric dinitrogen (N2) and processing it into a reactive form of nitrogen through enzymatic reduction. The study of BNF in non-leguminous plants has been difficult compared to nodule-localized BNF in leguminous plants because of the diverse sites of N2 fixation in non-leguminous plants. Identification of the involved N2-fixing bacteria has also been difficult because the major nitrogen fixers were often lost during isolation attempts. The past 20 years of molecular analyses has led to the identification of N2 fixation sites and active nitrogen fixers in tissues and the rhizosphere of non-leguminous plants. Here, we examined BNF hotspots in six reported non-leguminous plants. Novel rhizobia and methanotrophs were found to be abundantly present in the free-living state at sites where carbon and energy sources were predominantly available. In the carbon-rich apoplasts of plant tissues, rhizobia such as Bradyrhizobium spp. microaerobically fix N2. In paddy rice fields, methane molecules generated under anoxia are oxidized by xylem aerenchyma-transported oxygen with the simultaneous fixation of N2 by methane-oxidizing methanotrophs. We discuss the effective functions of the rhizobia and methanotrophs in non-legumes for the acquisition of fixed nitrogen in addition to research perspectives.

Elevated Atmospheric CO2 and Nitrogen Fertilization Affect the Abundance and Community Structure of Rice Root-Associated Nitrogen-Fixing Bacteria

“…R2-708 (OTU321) under aCO 2 treatment (Figure 5C). Rhizobium is a well-known N 2 -fixing bacterium that is frequently detected in legumes as well as in rice roots (Zahran, 1999;Bao et al, 2014a;Yoneyama et al, 2019) and other plants. Heterotrophic N 2 -fixing bacteria, including Rhizobium, are often inhibited by nitrogen inputs (Kumar et al, 2018).…”

“…N fertilization decreased the relative abundance of root-associated bacteria community, especially type II methanotrophs and Bradyrhizobium (Ikeda et al, 2014). Generally, N fertilizer inputs inhibit N 2 fixation and influence the N 2 -fixing bacterial community (Kumar et al, 2018), which can convert atmospheric N 2 gas to ammonium and make it available to plants as a major nutrient (Yoneyama et al, 2019). eCO 2 can increase the N demand for plants, which is beneficial for N 2 fixation (Luo et al, 2004).…”

Genotypic Variation of Endophytic Nitrogen-Fixing Activity and Bacterial Flora in Rice Stem Based on Sugar Content

“…Carbohydrates produced by photosynthesis are stored in the stem mainly as starch and sucrose in rice (Yoshida, 1972 ) as shown in this study ( Table 2 , Figure 2 ). In the mature stem of sugarcane, about 10–20% of the accumulated sugars were present in the apoplast and contributed to high endophytic BNF (Welbaum and Meinzer, 1990 ; Dong et al, 1994 ; Yoneyama et al, 2019 ). The shading experiment also indicated that changes in sugar are more crucial than starch for the fluctuation of N-fixing activity, since ARA in agpl1 decreased significantly by shading treatment in association with a large decrease in sugar as compared with Nipponbare ( Figure 3 ).…”

“…On the basis of the studies conducted, active expression of NifH, one of the proteins that compose the nitrogenase enzyme, is phylogenetically similar to that of the Bradyrhizobium sp., and Azorhizobium sp. was observed in the N-fixing sugarcane stems, sweet potato stems, and tuberous roots (Terakado-Tonooka et al, 2008 ; Fischer et al, 2012 ; Yoneyama et al, 2019 ). In rice roots as well, active BNF by methane-oxidizing methanotrophs on consuming CH 4 as a carbon source has also been reported (Bao et al, 2014 ; Shinoda et al, 2019 ).…”

Efeitos da conversão pastagem-canavial e da intensificação do sistema de pastagem na microbiota do solo associada ao ciclo do nitrogênio

“…A produção da soja representa 50% da área total cultivada com leguminosas, e é responsável por fixar 16,4 Tg N anualmente, o que equivale a quase 80% de todo nitrogênio fixado pelas leguminosas (HERRIDGE et al, 2008). Apesar de associações simbióticas com rizóbios não serem naturais com plantas não-leguminosas, trabalhos mostram que culturas como arroz, milho, cana-de-açúcar, e gramíneas são capazes de fixar N2 por meio de relações menos especializadas com microrganismos de vida livre ou associados às plantas (HERRIDGE et al, 2008;YONEYAMA et al, 2019).…”