Abstract:Aiming to understand the effects on the improvement of typical saline-alkali land in Northern Ningxia of China under different grasscrop rotation patterns, and on the composition characteristics and influencing factors of the bacterial community microbial diversity of saline-alkali soil,as well as discussing the possible mechanism of grass-crop rotation patterns to improve saline-alkali soil. A positioned experiment of crop and rotation system of Medicago sativa L. was carried out to discuss the effect on the mechanism for improving the saline-alkali soil through implementing different grass-crop rotation patterns, including continuous cropping(AA), fallowing after plowing(AF), rotating with Helianthus annuus L.(AO), Zea may (AC) and Sorghum dochna (AS). Total genomic DNA was isolated from the rhizosphere soils using a power soil DNA isolation kit. Then V4 sections of 16S rDNA were sequenced with the aid of the IlluminaHiSeq high-throughput sequencing technology and the diversity and structure of soil microbial communities in the rhizosphere soils were analyzed with QIIME. The relationship between soil physicochemical factors and bacterial community structure was also analyzed. The results showed that Proteobacteria, Actinobacteria, Acidobacteria were the dominant phylum in different grass-crop rotation patterns. Among them,the number of Proteobacteria was significantly higher in Helianthus annuus L. patternthan that of other grass-crop rotation patterns (P<0.05).The second dominant group, Actinobacteria, had the highest relative abundance in the pattern of fallowing after plowing, rotating with Zea mays. As of the third dominant group of Acidobacteria,the relative abundance of which was the highest in soils of rotating with Sorghum dochna. At the genus level, Arthrobacter was the dominant genus in saline-alkali soils of all grass-crop rotation patterns in Northern Ningxia. Alpha diversity index showed that the diversity and richness of soil bacterial community in fallowing after plowing pattern was significantly higher than that of other patterns, Sorghum dochna pattern were significantly lower than that of other patterns. The result of soil physicochemical properties showed that the values of total salt, pH value and alkaline phosphatase were the lowest in rotating with Helianthus annuus L. and the values of alkalyzable potassium, alkalyzable phosphorus were the highest in fallowing after plowing pattern. Speculating that alkalyzable potassium, pH value and catalase were the crucial factors influencing the bacterial community diversity among five grass-crop rotation patterns. Highthroughput sequencing analysis can obtain more comprehensive information of bacterial community diversity, and the changes of soil environmental factors after grass-crop rotation affected the structure of soil bacterial community, which provided correlations between bacterial composition and diversity with environmental factors.
