连作对枸杞根区土壤理化性质、农药残留和微生物群落的影响

Effects of Continuous Cropping on the Physiochemical Properties, Pesticide Residues,and Microbial Community in the Root Zone Soil of Lycium barbarum

连作障碍是限制枸杞优质高产的重要因素,为明确枸杞根区土壤特征对连作年限的响应,系统地对不同连作年限的枸杞根区土壤理化性质和农药残留量进行检测,并通过高通量测序技术表征了土壤细菌和真菌群落的特征.结果表明,枸杞连作显著增加了其根区土壤的全盐和吡虫啉含量,相较于连作2 a和9 a,连作15 a的枸杞根区土壤中全盐含量分别增加了51.97%和54.33%,吡虫啉含量分别增加39.58%和36.61%.碱解氮和速效钾含量呈现先增加后降低的趋势,相较于其他年限,连作9 a的枸杞根区土壤中碱解氮和速效钾含量分别增加16.94%~28.09%和18.31%~18.34%.相较于连作15 a,连作9 a的枸杞根区土壤中细菌群落的多样性和丰富度,以及真菌群落的丰富度显著增加.此外,连作年限的增加也增加了枸杞根区土壤假单胞菌属(Pseudomonas)、节杆菌属(Arthrobacter)、放射毛霉属(Actinomucor)和木霉属(Trichoderma)等植物有害病原菌的富集.土壤全盐、有机质、碱解氮和速效钾是影响枸杞根区土壤细菌群落分布的主要环境因子;土壤碱解氮、速效磷和铵态氮是影响枸杞根区土壤真菌群落分布的主要环境因子.此外,不同连作年限枸杞根区土壤细菌以代谢功能为主,特别是在连作9a的土壤中氨基酸代谢、能量代谢和核苷酸代谢最为丰度,而连作15 a的土壤中膜转运相关的功能基因丰度最高;不同连作年限枸杞根区土壤真菌则均以腐生营养型为主,病原交叉营养型次之.综上,长期连作诱导了枸杞根区土壤微环境的变化,增加了土壤中农药的残留和植物病原菌的富集,降低了土壤细菌和真菌群落的多样性.因此,在枸杞种植管理中要注意把控土壤养分的比例和农药用量,及时进行深耕深翻以及老龄植株的更替.

Continuous cropping is a common obstacle limiting the high quality and yield of Lycium barbarum(wolfberry).To clarify the response of soil characteristics of the wolfberry root zone to continuous cropping years,we systematically determined the physicochemical properties and pesticide residues of soils in the wolfberry root zone with different continuous cropping years.In addition,soil bacterial and fungal communities were characterized using high-throughput sequencing technology.The results were as follows:The content of total salt and imidacloprid in the root zone of wolfberry increased with increasing years of continuous cropping.Compared to that with 2 and 9 years,the total salt content in the root zone of wolfberry with 15 years of continuous cropping increased by 51.97%and 54.33%,respectively,and the imidacloprid content increased by 39.58%and 36.61%,respectively.Alkaline nitrogen and available potassium showed an increasing and then decreasing trend.Compared to that with 2 and 15 years,alkaline nitrogen and available potassium in the root-soil of wolfberry with 9 years of continuous cropping increased by 16.94%-28.09%and 18.31%-18.34%,respectively.The diversity and abundance of bacterial communities and the abundance of fungal communities were higher in the root-soil of wolfberry with 9 years of continuous cropping compared to that with 15 years of continuous cropping.In addition,the increase in continuous cropping years also increased the accumulation of harmful plant pathogens such as Pseudomonas,Arthrobacter,Actinomucor,and Trichoderma in the root zone of L.barbarum.Soil total salinity,organic matter,alkaline hydrolyzable nitrogen,and available potassium were the main factors influencing the distribution of bacterial communities.Soil alkaline hydrolyzable nitrogen,available potassium,and ammonium nitrogen were the main factors influencing the distribution of fungal communities.In addition,the soil bacteria in the root zone of L.barbarum were dominated by metabolic functions;in particular,amino acid metabolism,energy metabolism,and nucleotide metabolism were most abundant in the root soil of wolfberry with 9 years of continuous cropping,whereas the highest abundance of functional genes related to membrane translocation was found in the rootsoil of wolfberry with 15 years of continuous cropping.The soil fungi were all dominated by saprophytic trophic types,followed by pathogenic cross-nutrients in the root zone of L.barbarum.In conclusion,long-term continuous cropping induced changes in the soil microenvironment in the root zone of L.barbarum,increased soil residues of harmful pesticides and the enrichment of plant pathogens,and reduced the diversity of soil bacterial and fungal communities.Therefore,it is necessary to control the rate of application of soil nutrients and pesticides in the management of L.barbarum and to carry out deep ploughing and deep tilling in good time,and the turnover of old plants in the cultivation of L.barbarum.