Study On Soil Physicochemical Properties And Microbial Diversity In Agroforestry System Of Pecan

The initial planting density of pecan is high,which leads to the waste of land resources between rows,so plant some plants under the forest is necessary.However,the long-term effect of agroforestry management on soil is related to the growth and fruiting of the upper layer of pecan.The effects of agroforestry on soil physical and chemical properties and soil enzyme activities were studied in three different agroforestry models（pecan+Paeonia suffruticosa+Hemerocalliscitrina,PPH;pecan+Paeonia suffruticosa,PPS; pecan+Paeonia lactiflora Pall,PPL）and pure forest of pecan.Based on 16S r RNA and ITS2 amplicon sequencing technology,the effects of agroforestry on the community species diversity of soil microorganisms（bacteria and fungi）were analyzed,The purpose of this paper is to find out the agroforestry model for the growth and fruiting of pecan.The main conclusions are as follows:（1）Compared with the pure forest,the soil bulk density of PPH and PPL agroforestry decreased,while the soil moisture content and total soil porosity increased.After agroforestry,the soil electrical conductivity of 0-20 cm and 20-40 cm soil layer increased,but the improvement of soil physical properties was not obvious by PPS agroforestry.Compared with the pecan pure forest,the soil p H value decreased by 0.96%and 2.41%.There was a negative correlation between soil p H and the contents of soil total nitrogen（TN）,total phosphorus（TP）,ammonium nitrogen（NH₄⁺-N）,available phosphorus（AP）and available potassium（AK）,and the correlation degree was TN>AP>AK>TP>NH₄⁺-N.The contents of total phosphorus,total nitrogen,available potassium and total carbon in 0-20 cm soil layer were significantly positively correlated with soil Ca content,and PPS agroforestry significantly increased soil potassium,calcium and magnesium content.The content of available phosphorus decreased with the deepening of soil layer.（2）Agroforestry can improve some soil enzyme activities.In 0-20 cm soil,compared with the pure forest,the activities of urease,alkaline phosphatase and 1,4-β-N- acetylglucosaminidase in agroforestry system increased significantly.The soil polyphenol oxidase activity of PPH agroforestry was higher than that of other models.However,cellobiohydrolase,peroxidase andβ-1,4-glucosidase in pure forest were higher than those in other models.There is a correlation between soil enzyme activity and soil physical and chemical properties.There was a significant positive correlation between soil alkaline phosphatase activity and total nitrogen,soil moisture content,total phosphorus,available potassium and total carbon content.Soil cellobiohydrolase activity was significantly negatively correlated with ammonium nitrogen,available potassium,total nitrogen and total carbon.There was a significant negative correlation between soil polyphenol oxidase activity and soil bulk density,total phosphorus and total magnesium content.（3）Agroforestry is beneficial to increase the diversity and abundance of soil microbial community in woodland.Agroforestry has a certain influence on the diversity and structure of soil bacterial and fungal communities in 0-20 cm soil layer.The Alpha index of bacteria and fungi in PPS was the highest,followed by PPH.The Alpha index of bacteria and fungi in PPL was the lowest.The dominant bacteria in 0-20 cm soil layer were Proteobacteria,Acidobacteria,Gemmatimonadetes,Actinobacteria and Chloroflexi,in which Proteobacteria,Acidobacteria,Actinobacteria and Chloroflexi,had significant differences among different agroforestry patterns.The dominant fungi in 0-20 cm soil layer were Ascomycota,Basidiomycota and Zygomycota.Through redundant analysis of the potential relationship between soil microbial community structure and soil physical and chemical properties,it was found that total nitrogen,total phosphorus and nitrate nitrogen were the most key factors to explain the difference of bacterial community,and electrical conductivity and total potassium were the most key factors to explain the difference of fungal community.In a word,agroforestry of pecan can effectively increase the soil physical and chemical properties and enzyme activity,and increase the community diversity of soil bacteria and fungi.It is suitable to popularize the PPS agroforestry,followed by the PPH agroforestry.