连作、轮作对谷子根际细菌群落结构的影响

Effects of continuous cropping and rotation on rhizosphere bacterial community structure of millet

为探明谷子连作与轮作对土壤细菌群落组成的影响,利用高通量测序技术,结合土壤理化性质及酶活性,比较分析了撂荒地、玉米-谷子轮作、谷子连作2、3 a和5 a土壤细菌群落组成多样性。结果表明:谷子连作与轮作土壤均为碱性,pH为8.26~8.49,碱解氮、有机质、脲酶活性表现为轮作地最高,连作2 a开始降低,连作3 a达最低值,连作5 a又开始回升,速效钾、多酚氧化酶、过氧化氢酶以及蔗糖酶活性均是连作土壤高于轮作土壤。谷子连作与轮作土壤细菌在门水平上群落组成比较固定,但不同物种的丰度差异较大;菌群分析发现放线菌门、变形菌门以及酸杆菌门是谷子根际土壤优势菌群;菌群相对丰度在轮作土壤中高于连作土壤的有:变形菌门、酸杆菌门、拟杆菌门、厚壁菌门以及硝化螺旋菌门,低于连作土壤的有己科河菌门和绿弯菌门;Alpha多样性分析显示各组间菌群差异不显著,Beta多样性分析则显示连作、玉米-谷子轮作地和撂荒地土壤菌群分布差异较大;冗余分析(RDA)表明鞘氨醇单胞菌与pH、有效磷、碱解氮和有机质呈正相关,类诺卡氏菌与pH、有效磷、碱解氮、有机质、脲酶和过氧化氢酶呈正相关,轮作、连作、撂荒地组间根际土壤优势菌存在差异,LEfSe分析确定了谷子根际土壤特定标志物,其中轮作地的优势菌群为鞘氨醇单胞菌和类诺卡氏菌,3 a连作地的优势菌群为土壤红杆菌。综上所述,谷子连作土壤与轮作土壤相比,细菌的ASVs丰度减少,细菌群落分布差异较大;随着谷子连作年限增加,土壤养分呈先下降后上升趋势。

This study explored the effects of continuous millet cropping and rotation on soil bacterial community composition. Highthroughput sequencing technology combining soil physicochemical properties and enzymatic activities were used to analyze the diversity of soil bacterial community composition in abandoned, maize-millet rotation, and continuous cropping land with millet for 2, 3, and 5 years.The soil of millet continuous cropping and crop rotation was alkaline, with its pH ranging from 8.26 to 8.49. The alkali solution nitrogen,organic matter, and urease activity were highest in the rotation land, which began to reduce in 2-year continuous cropping soil, achieved the minimum in 3-year continuous cropping land, and rose again after continuous cropping for 5 years. The rapidly available potassium,polyphenol oxidase, catalase, and invertase values in the continuous cropping lands were higher than in the rotation land. The community composition of soil bacteria was fixed at the phylum level between continuous cropping and rotation of millet, but the abundance of different species differed significantly. Results showed that Actinobacteria, Proteobacteria, and Acidobacteria were the dominant bacteria in millet rhizosphere soil. The relative abundance of Proteobacteria, Acidobacteria, Bacteroides, Firmicutes, and Nitrocellulobacteria in rotation soil was higher than in the continuous cropping soil, whereas hexane and Chlorocurved bacteria in the rotation soil were lower. Alpha diversity analysis showed no significant difference among the groups, whereas Beta diversity analysis showed a significant difference between continuous cropping, maize-millet rotation, and abandoned land. Redundancy analysis showed that Sphinomonas was positively correlated with pH, rapidly available potassium, organic matter, and alkaline hydrolysis nitrogen, whereas Nocarnoid was positively correlated with pH, rapidly available phosphorus, organic matter, alkaline hydrolysis nitrogen, urease, and catalase. There were differences in the dominant bacteria of rhizosphere soil among the rotation, continuous cropping, and abandoned land groups. The linear discriminant analysis effect size determined specific soil markers in the rhizosphere soil, that the dominant bacteria in the rotation soil were Sphingomonas and Nocardioides, and that the dominant bacteria in the continuous cropping land for 3 years was Solirubrobacter. In conclusion, with the increase of continuous millet cropping years, the soil nutrients first decrease and then increase. The ASV abundance of bacteria decrease compared with rotation, and the bacterial community distribution is significantly different.