Abstract: To explore the improvement mechanism of soil environment and microbial community in saline‐alkali land by rotation systems of alfalfa（Medicago sativa L.） and salt‐tolerant gramineous crops，four planting patterns were established in the saline‐alkali land of the Ningxia Yellow River irrigation area，including continuous alfalfa cropping（M），alfalfa‐Hunan Jizi rotation（H），alfalfa‐maize rotation（Y），and alfalfa‐sorghum rotation（G）.The effects of different planting patterns on soil physicochemical properties and bacterial community diversity were systematically analyzed. The results showed that compared with continuous alfalfa cropping，all rotation patterns significantly reduced soil total salt content，as well as the contents of Na⁺，Ca²⁺，and Mg²⁺. Among them，the alfalfa‐sorghum rotation exhibited the optimal salt reduction effect，with the soil total salt content decreased by 79.2% compared with continuous alfalfa cropping. Rotation practices markedly increased the contents of soil availabl phosphorus，total phosphorus，and organic matter，and the alfalfa‐maize rotation showed the best improvement effect，with increases of 67.1%，38.3%，and 147.7% respectively relative to continuous alfalfa cropping. In terms of bacterial diversity，rotation patterns significantly improved soil bacterial richness，with a notably higher Chao1 index than that of continuous alfalfa cropping. Other alpha diversity indices were also superior to those of continuous cropping，though the differences were not significant.In terms of species composition，the relative abundances of Proteobacteria，Acidobacteriota and Actinobacteriota in soils with continuous alfalfa monoculture were all higher than those under rotation systems. Principal coordinate analysis（PCoA） further indicated that rotation enhanced the plasticity of soil bacterial community structure with a greater intra‐group dispersion. In conclusion，the rotation of alfalfa with gramineous crops could effectively improve the physicochemical properties of saline‐alkali soil and optimize the structure of soil bacterial community.Specifically，alfalfa‐sorghum rotation and alfalfa‐maize rotation present outstanding comprehensive improvement effects.

Key words: Saline‐alkali soil, Alfalfa（Medicago sativa L.）, Rotation pattern, Soil physicochemical property, Bacterial diversity, Bacterial community structure

摘要： 为探究紫花苜蓿（Medicago sativa L.）与耐盐碱禾本科作物轮作对盐碱地土壤环境及微生物群落的改良机制，在宁夏引黄灌区盐碱地设置紫花苜蓿连作（M）、紫花苜蓿-湖南稷子轮作（H）、紫花苜蓿-玉米轮作（Y）、紫花苜蓿-高粱轮作（G）共4种模式，系统分析其对土壤理化性质及细菌群落多样性的影响。结果表明，与紫花苜蓿连作相比，轮作可显著降低土壤全盐含量以及Na^⁺、Ca^²⁺、Mg²⁺含量，其中紫花苜蓿-高粱轮作处理降盐效果最佳，其土壤全盐含量较紫花苜蓿连作下降79.2%；轮作可显著提高土壤速效磷、全磷及有机质含量，以紫花苜蓿-玉米轮作处理效果最佳，较紫花苜蓿连作分别提升67.1%、38.3%、147.7%。在细菌多样性方面，轮作可显著提高土壤细菌丰富度，其Chao1指数显著高于紫花苜蓿连作，其他Alpha多样性指数也均优于连作，但差异不显著。物种组成上，紫花苜蓿连作土壤中变形菌门、酸杆菌门和放线菌门的相对丰度均高于轮作。主坐标分析进一步表明，轮作可提升细菌群落结构的可塑性，其组内离散度较大。综上，紫花苜蓿与禾本科作物轮作可有效改良盐碱地土壤理化性状、优化土壤细菌群落结构，其中紫花苜蓿-高粱轮作、紫花苜蓿-玉米轮作综合改良效果较突出。

关键词: 盐碱地, 紫花苜蓿, 轮作模式, 土壤理化性质, 细菌多样性, 细菌群落结构