连作木薯对土壤理化性质及细菌群落演替的影响

Effects of continuous cropping of cassava on soil physicochemi⁃cal properties and bacterial community succession

【目的】研究连作木薯对非根际和根际土壤理化性质变化及细菌群落演替的影响,为系统阐明木薯连作障碍形成机制及其缓解措施研发提供理论依据。【方法】以木薯品种华南205为试验材料,在撂荒地上连续种植3年,每年木薯块根成熟期(植后250 d)采集土壤样品。结合土壤农化分析、高通量测序技术和生物信息学手段,研究连作木薯对非根际和根际土壤理化性质及细菌群演替的影响。【结果】与种植第1年木薯相比,连作2年和3年的木薯非根际和根际土壤pH及有机质、碱解氮和速效磷含量降低,脲酶活性提高,除速效磷外,其他指标的变化均达显著水平(P<0.05,下同)。连作木薯会引起土壤细菌群落多样性及丰富度降低,其中根际土壤细菌群落多样性及丰富度下降速度比非根际土壤慢。连作木薯非根际与根际土壤细菌群落的分类和系统发育Beta多样性存在显著差异。连作木薯非根际和根际土壤的优势菌门均为放线菌门(Actinobacteriota)、变形菌门(Proteobacteria)、绿弯菌门(Chloroflexi)、厚壁菌门(Firmicutes)、酸杆菌门(Acidobacteriota),主要优势菌属均为芽孢杆菌属(Bacillus)、norank_f_Roseiflexaceae、norank_f_norank_o_Vicinamibacterales、norank_f_norank_o_Gaiellales。在操作分类单元(OTU)水平,不同连作年限木薯的非根际和根际土壤细菌群落组成存在显著或极显著(P<0.01)差异。土壤的细菌群落结构与理化性质相互影响,对细菌群落影响较大的环境因子排序为碱解氮含量>有机质含量>pH>速效磷含量>脲酶活性。【结论】连作会导致木薯非根际和根际土壤理化性质、细菌群落多样性和丰富度发生变化,土壤理化性质和细菌群落结构均在连作第3年出现明显劣化。木薯土壤理化性质变化与土壤细菌群落结构差异存在一定相关性,有益菌丰度降低可能是木薯连作造成土壤细菌群落劣化演替的重要原因之一。

【Objective】The aim of this study was to investigate how continuous cropping of cassava affected the physicochemical properties of non-rhizosphere and rhizosphere soils,as well as the succession of bacterial communities,and thus providing a theoretical basis for understanding the formation of cassava continuous cropping obstacles.【Method】The cassava variety South China 205 was continuously cultivated in an abandoned field for three years.The soil were sampled at cassava root tuber maturity stage(250 d after planting)in each year.Combining soil agrochemical analysis,high-throughput sequencing technology and bioinformatics methods,effects of continuous cassava on non-rhizosphere and rhizosphere soil physicochemical properties and bacterial group succession were studied.【Result】The results showed that pH,organic matter,alkali-hydrolyzed nitrogen and available phosphorus contents of non-rhizosphere and rhizosphere soil of cassava were decreased and urease activity was increased in two and three years of continuous cropping compared with the first year of planting,and except available phosphorus content,the changes of other indexes reached significant level(P<0.05,the same below).Continuous cropping of cassava led to a decrease in the diversity and richness of soil bacterial communities.However,the decline rate in rhizosphere soil bacterial communities was slower than that in non-rhizosphere soils.There were significant differences in the classification and phylogenetic Beta diversity of non-rhizosphere and rhizosphere soil bacterial communities of continuous cropping cassava.The dominant bacterial phyla in non-rhizosphere and rhizosphere soils were Actinobacteriota,Proteobacteria,Chloroflexi,Firmicutes and Acidobacteriota.The main dominant bacterial genera were Bacillus,norank_f_Roseiflexaceae,norank_f_norank_o_Vicinamibacterales and norank_f_norank_o_Gaiellales.At the operational taxonomic unit(OTU)level,significant or extremely significant(P<0.01)differences were found in the composition of soil bacterial communities in non-rhizosphere and rhizosphere soils of cassava at different continuous cropping years.The structure of soil bacterial communities was mutually affected by soil physicochemical properties,the environmental factors affected bacterial community ranked as alkaline hydrolysis nitrogen content>organic matter content>pH>available phosphorus content>urease activity.【Conclusion】Continuous cropping can lead to changes in non-rhizosphere and rhizosphere soil physicochemical properties,bacterial community diversity and richness,and soil physicochemical properties and bacterial community structure of cassava greatly deteriorate in the third year of continuous cropping.Soil physicochemical properties are correlated to structure of bacterial communities at certain extent.Notably,the decrease in the abundance of beneficial bacteria might be an important reason for the deterioration of soil bacterial community succession caused by cassava continuous cropping.