The response of microbial community in aerobic rice rhizosphere that affected by various plant growth stages and soil types

Aims@#Aerobic rice is a potential crop introduced to encourage water conservation in rice planting. However, a decline of aerobic rice yield has been reported and thus this study was initiated with the aim to observe the response of microbial community in this environment which are exposed to various plant growth stage and soil types. @*Methodology and results@#To determine the effect of soil types such as peat and sandy clay loam on microbial community. A total of four growth stages were tested namely vegetative, reproductive, ripening and maturing. To determine the influence of growth stages and soil types towards microbial community in aerobic rice, Biolog Ecoplate™ technique was used to quantify the response of microbial community through microbial functional diversity and carbon source utilization. The abundance of culturable aerobic bacteria, fungi, actinomycetes, nitrogen-fixing microorganism and phosphate-solubilizing microorganism were determined using five different selective media. Soil physical and chemical properties as well as total nitrogen in plant tissues were also determined. It was found that microbial functional diversity during plant growth (except for microbial evenness) varied between the soil types. Correlation analysis revealed different relationships between carbon source utilization and microbial functional diversity in both soil types. @*Conclusion, significance and impact of study@#Microbial community in rhizosphere responded according to plant development which is primarily determined by soil type. Therefore, it is concluded that soil type particularly the soil physical and chemical properties are important factors in shaping the microbial community by directly influencing the rhizosphere environment.

Eliminating aluminum toxicity in an acid sulfate soil for rice cultivation using plant growth promoting bacteria.

Aluminum toxicity is widely considered as the most important limiting factor for plants growing in acid sulfate soils. A study was conducted in laboratory and in field to ameliorate Al toxicity using plant growth promoting bacteria (PGPB), ground magnesium limestone (GML) and ground basalt. Five-day-old rice seedlings were inoculated by Bacillus sp., Stenotrophomonas maltophila, Burkholderia thailandensis and Burkholderia seminalis and grown for 21 days in Hoagland solution (pH 4.0) at various Al concentrations (0, 50 and 100 µM). Toxicity symptoms in root and leaf were studied using scanning electron microscope. In the field, biofertilizer (PGPB), GML and basalt were applied (4 t·ha-1 each). Results showed that Al severely affected the growth of rice. At high concentrations, the root surface was ruptured, leading to cell collapse; however, no damages were observed in the PGPB inoculated seedlings. After 21 days of inoculation, solution pH increased to >6.0, while the control treatment remained same. Field study showed that the highest rice growth and yield were obtained in the bio-fertilizer and GML treatments. This study showed that Al toxicity was reduced by PGPB via production of organic acids that were able to chelate the Al and the production of polysaccharides that increased solution pH. The release of phytohormones further enhanced rice growth that resulted in yield increase.