Rice is a monocot, non-leguminous crop, suggesting that associative N 2-fixing microbes play a key role in in situ nitrogen fortification (Zaki et al. Nitrogen-fixing bacteria can transform atmospheric nitrogen into fixed nitrogen, which will be further used by plants. Therefore, it is pertinent to find alternative nitrogen sources to avoid these problems.īiological nitrogen fixation (BNF) can substitute for some chemical nitrogen fertilizer use in rice cultivation (Choudhury and Kennedy 2004), thus reducing the afore-mentioned environmental problems to some extent. Moreover, the price of chemical nitrogen fertilizers has been increasing. In addition, application of excessive nitrogen fertilizers to increase yield may result in reducing grain yield and quality, low N use efficiency, and environmental pollution (Deng et al. However, nitrogen deficiency is often a limiting factor for rice growth, due partly to low nitrogen use efficiency caused by ammonia volatilization, denitrification, and leaching losses that cause environmental problems (Ponnamperuma 1972 Choudhury and Kennedy 2004). Of these chemical fertilizers, nitrogen fertilizers considerably affect rice yields because rice growth highly depends on nitrogen fertilizers that are closely related to the photosynthetic capacity of leaves, development of tillers, differentiation of spikelets, and properties of grains (Choudhury et al. One of technological methods used to increase rice yields is to apply more fertilizers to high-yield rice varieties. Moreover, it has been suggested that rice yields need to be increased by 40% or even more in the next few decades to meet the requirements of a rapidly increasing world population (Khush 2005). With reducing rice production areas due to urbanization and other cultural challenges, improvement in productivity is vital to ensure food security. Rice is one of the main food crops in the world, being consumed by about 50% of world and 85% of Asian populations (Sahoo et al. This study contributes to the selection of suitable Azotobacter strains for developing biofertilizer formulations and soil management strategies of Azotobacter for paddy fields. chroococcum CHB 869 may be used to develop biofertilizers for rice cultivation because they significantly promoted rice growth. Members of the same Azotobacter species showed diverse plant growth-promoting traits, suggesting that the 98 strains isolated in this study may not equally effective in promoting rice growth. In addition, the species diversity of Azotobacter was significantly related to soil pH, Mn, and Zn. Strains within individual Azotobacter species showed diverse profiles in carbon source utilization. beijerinckii had the highest level of nucleotide diversity. chroococcum was predominant (51.0%) but A. Four species of Azotobacter were identified within these 98 strains, including A. Of the 98 strains isolated in this study, 12 were selected to evaluate their effects on rice growth. The characteristics of these Azotobacter strains were analyzed including carbon source utilization and plant growth-promoting traits such as nitrogen fixation activity, indole acetic acid production, phosphate-solubilizing ability, and siderophore secretion. A total of 98 Azotobacter isolates were isolated from 27 paddy fields, and 16S rRNA gene sequences were used to identify Azotobacter species. The purposes of this study were to characterize Azotobacter species isolated from rice rhizospheres in Taiwan and to determine the relationship between the species diversity of Azotobacter and soil properties. Azotobacter species, free-living nitrogen-fixing bacteria, have been used as biofertilizers to improve the productivity of non-leguminous crops, including rice, due to their various plant growth-promoting traits.
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