Diversity of diazotrophic cyanobacteria in the acidified paddy fields around Lake Dongting and adaptation mechanisms of the dominant species to soil acidification

There is gap in production and demand of grain in our country, the demand for import of grain of cereal category alone is as high as 15 billion kilograms or so every year. At the same time, the long-term excessive use of chemical nitrogen fertilizer has led to the decline of soil pH by about 0.2 units per 10 years. Soil acidification has led to the appearance of large areas of low-yield fields and even tillage obstacles in many main grain-producing areas of our country, which seriously hindered the sustainable development of agriculture and increased the gap between production and demand of grain in our country. Reducing the use of chemical nitrogen fertilizer is the main way to curb soil acidification. Nitrogen-fixing cyanobacteria could reduce the use of chemical nitrogen fertilizer in paddy fields through biological nitrogen fixation. The excavation work of cyanobacterial resources in paddy fields of our country was mainly concentrated before the 1980s, and little work was done in the past 40 years. Compared with the past, the physical and chemical properties of paddy soil have changed significantly, but the excavation of cyanobacterial resources in paddy fields lags behind seriously. Nitrogen-fixing cyanobacteria previously isolated from non-acidified rice fields are difficult to form dominant populations in acidified rice fields or even fail to survive. The inoculation of nitrogen-fixing cyanobacteria isolated from acidified rice fields could better adapt to the environment of acidified rice fields and play their ecological functions of biological nitrogen fixation and nitrogen input in rice fields. However, there is no specific N-fixing cyanobacteria germplasm bank for acidified rice fields in China and abroad. Our previous sampling survey results showed that although a large number of rice fields around Dongting Lake area were acidified, nitrogen-fixing cyanobacteria resources were still rich and had great mining and application value.This project aims to meet the needs of national sustainable agricultural development and high grain yield. From the perspective of exerting the ecological function of nitrogen input to cyanobacteria-nitrogen fixation in rice fields and reducing the use of chemical nitrogen fertilizer, aiming at the technical bottleneck that it is difficult for the isolated cyanobacteria-nitrogen fixation to form dominant populations in acidified rice fields, or even to survive, according to the characteristics of microbial ecological adaptation, To explore the depth of nitrogen-fixing cyanobacteria resources in acidified rice fields around Dongting Lake region, and to analyze the adaptive mechanism of dominant nitrogen-fixing cyanobacteria in acidified rice fields to soil acidification. Our results would lay a theoretical foundation for reducing the amount of chemical nitrogen fertilizer in acidified rice fields using N-fixing cyanobacteria, and provide the germplasm resource support for algal species.