Soil Microbial Diversity And Alleviating Effects Of Melatonin On Continuous Cropping Yugan Pepper Seedlings

Pepper is the pillar industry of vegetable production in Jiangxi Province.With the growth of market demand and the limited arable land area,continuous cropping phenomenon is increasingly serious in facility cultivation.At present,the research mainly focuses on the physiological mechanism of pepper and the accumulation of soil toxic substances,and the microbial research is insufficient.This study analyzed the effects of continuous cropping on soil microbial community diversity of Yugan pepper based on high-throughput sequencing technology,and alleviated the effects of continuous cropping on seedlings by spraying melatonin.The results are as follows:1.The total amount of microorganisms in continuous cropping group（TM）was higher than that in normal cropping group（CK）,the Bacteria/Fungi value was always lower than that in CK,and the proportion of fungi was increased.Pearson correlation analysis showed that organic matter was significantly positively correlated with soil p H value and total phosphorus content,while available phosphorus and total nitrogen content were extremely significantly positively correlated.The content of available potassium was negatively correlated with bacterial community and total microbial community.2.Analysis of yield and quality of Yugan pepper showed that continuous cropping resulted in serious reduction of pepper yield.The fruit longitudinal diameter and fruit shape index of TM decreased significantly,and the yield per plant was further reduced by 28.25%compared with CK.Further analysis of pepper quality showed that TM significantly reduced the content of vitamin C by 6.5%,but compared with CK,TM increased the content of soluble sugar and total capsaicin,and had no significant difference in soluble protein.3.Based on the next-generation high-throughput sequencing technology,the effects of continuous cropping on pepper rhizosphere soil microbial community were analyzed.The results are as follows:TM obtained more fungi and bacteria Operational taxonomic units than CK,and fungal diversity analysis showed that Simpson index increased and Shannon index decreased,indicating that TM fungal community richness decreased.We consider that continuous planting of pepper contributes to the maintenance of soil microbial activity,but the proportion of TM fungi is increasing,and the soil is gradually changing from bacterial to fungal soil.Species difference analysis showed that the relative abundance of beneficial bacteria was continuously decreasing in TM,while the relative abundance of harmful fungi was continuously increasing.Among them,Firmicutes accounted for 8.43%in TM.Continuous cropping resulted in an increase in the proportion of Ascomycota and Fusarium in the soil,and the relative abundance of coectomycetes,maletohycetes and discetes in TM was increased by 145.9%,228.8%and 79.4%compared with CK,while the relative abundance of beneficial fungi,cocciocoetes and trichocetes,was significantly decreased compared with CK.The beneficial bacteriaβ-proteobacteria,blastomonas,sphinospilibacida,cyanobacteria,fuscida and acidobacteria＿Gp1decreased significantly compared with CK;Continuous cropping significantly reduced the relative expression abundance of dominant bacteria Sphingomonas and Gemmatimonas,and increased the expression abundance of Lacibacterium.Significantly increased the relative expression abundance of Mycochlamys,Coprinellus,Botryotrichum and Fusarium in dominant fungi.These results may be the direct cause of deterioration of pepper rhizosphere soil microflora.4.Melatonin increased seedling growth potential by increasing plant height,true leaf number and chlorophyll content under continuous cropping.The stomatal conductance was improved by increasing stomatal diameter,which contributed to gas exchange,net photosynthetic rate（Pn）and instantaneous water use efficiency（WUEi）,and promoted photosynthetic carbon accumulation and water use of pepper seedlings.According to the physiological indexes of leaves and roots,25μmol/L melatonin can increase soluble protein content,decrease MDA and H₂O₂ content and improve the activities of antioxidant enzymes（CAT,SOD and POD）in leaves,so as to alleviate the stress of pepper in adversity and improve the resistance of pepper under continuous cropping obstacle.