Analysis On Ecological Characteristics Of Rice Rhizosphere In Dry-Raised Seedlings

Dry-raised seedlings rice cultivation is a key measure for saving water, manpower, seed and fertilizer, and increasing yield and precocity related other characteristics. Already reported, experimental studies for dry-raised seedlings are mostly about the technical control measures and the physiological response mechanism of rice seedlings, but its rhizosphere ecological processes rarely reported. In this paper, by using the conventional rice line Jinhui-809 with large spikes as experimental material, we explored the dynamic changes of ecological factors and the changes in the rhizospheric microbial community structure in dry-raised seedlings. The main results were showed as follows.(1) Compared to the moist-raised seedlings, the physiological changes of seedlings and rice yield after transplanting under the way of dry-raised seedlings were discussed. Results showed that dry-raised seedlings could dramatically increase the concentration of GA3, ABA and IAA but reduce the content of ZT of root on the seedlings stage, boosted the accumulation of rice seedling root activity and dry matter, promoted the tillers occurrence after transplanting and improved the rice tiller rate, ultimately promoted the formation of high-yielding rice.(2) The ecological factors of rice rhizospheric soil were dynamically monitored in field trial. The results revealed that under the cultivation of dry-raised seedlings of moisture received strict control, the pH value sharply decreased, but the soil conductivity and temperature were significantly increased. Furthermore, the soil nutrients under different seedling-raising ways were determined, indicating that the cultivation of dry-raised seedlings could sharply increase the contents of nitrate nitrogen, ammonium nitrogen, available phosphorus, available potassium and organic carbon. Meanwhile, the activities of sucrase, urease, acid phosphomonoesterase, nitrate reductase and catalase associated with the C, N, P element transformation and dehydrogenase which described the diversity of microbial community structure were all enhanced, but the activities of nitrate reductase which involved in denitrification was significantly decreased.(3) Dual-end high-throughput sequencing methods of Illumina MiSeq was used to analysis the changes in the rhizospheric microbial community structure in dry-raised seedlings. The results showed that the diversity indexes of bacterial community became higher under the cultivation of the dry-raised seedlings compared to the moist-raised seedlings. While the dominant populations of rhizospheric bacterial community were further analyzed, it can be found that the proportion of bacteria relating to the recycling of soil nutrients increased dramatically under the way of dry-raised seedlings, including nitrifying bacteria (Nitrospira), Azotobacter (Rhizobiales, Hyphomicrobiaceae), Ammonia Oxidizing Bacteria (Rhodanobacter), photosynthetic bacteria (Rhodospirillaceae, Sphingomonas, Rhodoplanes), Phosporus-solubilizing bacteria (Xanthomonadaceae) and Potassium-solubilizing bacteria(bacillus), etc. In addition, the ratio of Bacillales, Pfseudomonas and Rhizobium which contain large amounts of Plant Growth-Promoting Rhizobacteria (PGPR) also increased significantly in the rhizosphere soil of dry-raised seedlings, thus contributing to the growth of the roots of dry-raised seedlings.In summary, dry-raised seedlings, by controlling moisture content of the soil, regulated the changes in soil pH, soil conductivity and temperature to improve the soil ecological environment, enhaned the proportion of bacteria relating to the nutrients recycling, and increased the activities of related soil enzymes and the availability of soil nutrients. Meanwhile, the number of rich PGPR bacterial community responded to the regulation of dry-raised seedlings significantly increased, regulated the content of the hormones related to root growth along with the increased root growth. All above conducive parameters triggered the formation of strong seedlings. In short, this study illustrated the physiological and ecological mechanisms of seedlings rhizosphere under the way of dry-raised seedlings, and deepen the theory of dry-raised cultivation develop the stong seedlings, which laid the foundation for the directional regulation of the rhizosphere of rice high-yield in future.