Diversity Of Microbial Community In Flooded And Non-flooded Paddy Fields

Rice (Oryza sativa) is one of the main foodstuffs of Chinese people. More than 30% crop field is used for rice cultivation in China. It provides 45% of crop yields in china. Because of landform limitation and in order to obtain a better yield, rice is usually planted under flooded conditions. Owing to the lack of water resource, landform and other factors, part of rice is planted in non-flooded fieldS. But the water consumption is greatness under the conventional cultivation of rice. It is estimated that the quantity of water used for irrigation takes up 65-80 percent of the total quantity water used for farm. China is short of fresh water resource. Water is becoming the main factor that restricts the agriculture development.This research studied the microbial characteristics of the flooded and non-flooded paddy soils at rice plantation of Dengjia Town, Yujiang County, Jiangxi province. The number of microorganisms, partial of physiological function groups and the diversity of microbial communities in in 0-5,5-10 and 10-15cm depth of flooded and non-flooded paddy fields were studied based on the plate count method, MPN(most probable number) method and molecule biology method of ARDRA (amplified ribosomal DNA restriction analysis). At the same time, the enzyme activity of key enzymes in nitrogen cycles, carbon cycles and phosphorous cycles were studied. The difference of diversity and the number of methanogen in flooded and non-flooded paddy fields were also studied. The aim of this study is to offer theoretics gist for reasonable and economical cultivation manner of rice. The main results of this study are as follows:The number of microorganism decrease with the increasing depth of Soil layers in the same paddy fields. The number of microorganism of topsoil was 10⁸, but the number of microorganisms of 10-15cm soil layers was 10⁷. The number of microorganiSm of flooded paddy fields is higher than that of the same layers soil in non-flooded paddy fields. although the number of microorganism was the same level. The results of partial functional groups counts Showed that the number of functional groups decrease with the depth of soil layers increased in the same paddy fields. The number of functional groups of flooded paddy fields is more than that of the same layers Soil in non-flooded paddy fields. But the changing trend of denitrifying bacteria was reverse compared with other functional groups.Bacteria diversity and its space distribution in 0～5,5～10 and 10～15 cm depth of flooded and non-flooded paddy fields were studied based on the molecular method of ARDRA (amplified ribosomal DNA restriction analysis). The results indicted that in flooded paddy fields, the bacterial types were very abundance in different depth of rice soils, there were significant discrepancy in bacteria diversity among different depth of soil because of the influence of soil moisture, the soil depth, the content of carbon and other factors. Bacterial community was most abundance and showed remarkably uniform distributions, and all species were nearly equally abundant in surface soil. There were 459 kinds of OTUs in 525 clones of topsoil bacterial clones of flooded paddy fields libraries and 452 kinds of OTUs in 522 clones of topsoil bacterial clone libraries of non-flooded paddy fields.The bacteria community diversity in 10～15 cm depth soil were lower than that in surface soil, but showed dominant groups of bacterial community. There were 372 kinds of OTUs in 507 clones of 10～15 cm layer soil bacterial clone libraries of flooded rice fields and 380 kinds of OTUs in 541 clones of 10～15 cm layer soil bacterial clone libraries of non-flooded paddy fields.The comparability of bacteria community in different depth soil was very low. These results indicate that the structures of soil bacteria communities are complex. The bacterial community diversity in soil with higher water content was higher than that of paddy soil with lower water content at the same depth soil, but the discrimination was not significant.The activity of urease, phosphatases and cellulsase decreased with the soil layers increased in flooded and non-flooded paddy fields, but the catalase activity is on ther way round. As a whole, the enzymes activity in flooded paddy fields is higher than that in non-flooded paddy fields.Through correlation analysis, there were different degree positive correlation between soil enzyme activity of urease, phosphatase and cellulsase and the number of microorganism ,soil fertility; but there was a negative relation between catalase activity and the number of microorganism, soil fertility; there were also positive correlation between the number of microorganism and soil fertility to different degree.The number of methanogen was 8.25×10⁶ cfu.g^-1 dry soil in flooded paddy fields and 4.16×10³ cfu.g^-1 dry soil in non-flooded paddy fields; There were 47 kinds of OTUs in 162 clones in flooded rice fields and 35 kinds of OTUs in non-flooded rice fields based on the molecular method of PCR-RFLP. From the above data, we can concluded that the number of methanogen and the methanogen diversity in flooded paddy fields were more than those in non-flooded paddy fields.