Ecological characteristics of rice rhizosphere of dry-raised seedlings

The dry-raising technique at rice seedling stage is an important cultivation method of rice that not only saves water, but also favors high yield production. To study the ecological characteristics of rice rhizosphere soils of dry-raised seedlings, the plant morphological index, ecological factor, soil nutrient effectiveness and bacterial community diversity of rhizosphere soils were investigated in a paddy field. The results showed that compared with moist-raised seedlings, shoot dry weight, root length, root dry weight, root-shoot ratio and white root number of dry-raised seedlings increased by 3.02%, 21.99%, 18.93%, 15.10% and 200.00%, respectively, but plant height decreased by 32.31%. Monitoring of ecological factor showed that soil water content of dry-raised seedlings was 15%17%. Under dry-raising condition, soil pH was decreased by 7.94% and electrical conductivity and temperature were decreased soil by 244.62% and 23 ℃, respectively, compared with those under moist-raising condition. The activities of phosphatase, invertase, urease, catalase and dehydrogenase in rhizosphere soils also increased by 166.66%, 518.85%, 131.98%, 102.70% and 84.36%, respectively, under dry-raised system at rice seedling stage, while nitrate reductase decreased by 72.95%. Dry-raising condition favored the conversion of soil organic matter and energy. This in turn increased soil organic matter, NO₃^-N, NH₄⁺-N, available K and available P in rhizosphere soil of dry-raised seedlings respectively by 89.27%, 320.11%, 56.95%, 50.85% and 184.75%. Finally, 16sRNA high-throughput sequencing analysis showed that Chao1 and Shannon-Wiener index for bacterial was higher in rhizosphere soil of dry-raised seedlings than those of moist-raised seedlings. Analysis of soil microorganism biota revealed that the proportions of Alphaproteobacteria, Gammaproteobacteria, Bacteroidetes, Chloroflexi, Nitrospirae, Acidobacteria, Gemmatimonadetes, Planctomycetes and Actinobacteria increased in rhizosphere soil of dry-raised seedlings, while the proportions of Firmicutes and Betaproteobacteria decreased. Function analysis on dominant populations of rhizospheric bacterial community showed that dry-raising system at rice seedling stage accelerated the growth of soil nutrient conversing bacteria. This included nitrifying bacteria, azotobacter, ammonia oxidizing bacteria, photosynthetic bacteria, phosphorus and potassium-solubilizing bacteria. In addition, the ratio of bacillales, pfseudomonas and rhizobium containing large amounts of plant growth-promoting rhizobacteria also increased significantly in rice rhizosphere soil of dry-raised seedling, which favored root growth. In summary, the cultivation of dry-raised seedling by controlling soil moisture content changed the pH, electric conductivity, temperature and bacteria diversity of rhizosphere soils of rice seedlings. This in turn favored the development of strong seedlings.