Study On The Formation Mechanism Of Dual Mycorrhizae Based On Rhizosphere Microorganisms,Soil Physicochemical Properties And Plant Characteristics

Plant growth requires gaining water and mineral nutrients from soil by roots.Plant roots have developed diverse strategies to facilitate nutrient uptake during evolution.It has been known that more than 90% of land plants can form symbionts(mycorrhizae)with mycorrhizal fungi to enhance nutrient uptake.Generally,mycorrhizae are divided into four types according to different morphological and anatomical characteristics,such as arbuscular mycorrhiza(AM),ectomycorrhiza(ECM),ericoid mycorrhiza(ERM)and orchid mycorrhiza(OM).Most plants usually form symbiotic structures with one type of mycorrhizal fungi,but a growing number of studies have recently found that some plants can form dual mycorrhizal structures with both AM fungi and ECM fungi.In this study,we sampled thin roots of 183 adult individuals from 38 tree species in the 25-ha subtropical forest dynamic monitoring plot in Baishanzu,Zhejiang Province,and explored what factors contributed to the dual mycorrhizal formation of tree species.Once the root samples were collected,mycorrhizal status of plants were identified by microscopic examination.The individuals of the identified dual mycorrhizal plants were further categorized into the dual mycorrhizal group and the non-dual mycorrhizal group.The rhizosphere microorganisms,soil physicochemical properties and plant traits among different mycorrhizal plants,the two groups of dual mycorrhizal plants were compared to explore the potential factors underlying the formation of dual mycorrhizae.The main conclusions of this study are as follows:(1)Through sampling and observing root infection of 183 adult individuals from 38 tree species in 10 families,six dual mycorrhizal tree species were found in this study,including Lithocarpus brevicaudatus,Lithocarpus hancei,Castanopsis eyrie,Quercus engleriana and Fagus lucida from Fagaceae,and Pinus taiwanensis from Pinaceae.The remaining 29 tree species were AM species and three were ECM tree species.Both AM and ECM colonization rates in dual mycorrhizal colonization was lower in transport fine roots than absorptive fine roots.Moreover,there was a significant negative correlation between AM colonization rate and ECM colonization rate in dual mycorrhizal colonization(P < 0.05).(2)In terms of rhizosphere microorganisms,this study focused on soil fungi.There were significant differences in soil fungal abundance between the two groups of dual mycorrhizal plants(P < 0.05),but the ? diversity and ? diversity of fungal community showed no significant difference.Furthermore,both Archaeorhizomyces and Chaetosphaeria showed significant differences among different mycorrhizal plants and the two groups of dual mycorrhizal plants.Dual mycorrhizae was more likely to occur when there are Archaeorhizomyces of higher abundance and Chaetosphaeria of lower abundance in soil.(3)There were significant differences in the nitrate nitrogen content between the dual mycorrhizal group and the non-dual mycorrhizal group(P < 0.05).Meanwhile,the soil available phosphorus content is lower and the soil total phosphorus content is higher in dual mycorrhizal group.This may be due to soil physicochemical properties play a role together with rhizosphere microorganisms.In places with high organic nutrient content,the high abundance of soil saprophytes enables plants to form AM symbiosis that require less carbon thus maximizing investment-return.(4)The diameter at breast height(DBH)of the dual mycorrhizal group was significantly smaller than that of the ECM group(P < 0.05).In other words,dual mycorrhizal colonization more likely occured in juvenile trees.Meanwhile,with increase of individual DBH,AM infection rate decreases while ECM infection rate increases.Rhizosphere microorganisms,soil physicochemical properties and plant traits were comprehensively analyzed.It was found that soil physicochemical properties had the strongest correlation with dual mycorrhizal formation,followed by rhizosphere microorganisms,and plant traits had the weakest correlation with dual mycorrhizal formation.In conclusion,this study shows that soil fungal community,soil physicochemical properties and root traits are related to the formation of dual mycorrhizae,and thus affected the dual mycorrhizal formation in plants.Specifically,Archaeorhizomyces and the total phosphorus content possibly promote the formation of dual mycorrhizae while the available phosphorus content and DBH are negatively correlated with dual mycorrhizal formation.Consequently,soil microorganisms,soil physicochemical properties and plant traits were considered comprehensively to explore the potential factors driving the formation of dual mycorrhizae and laying a foundation for further understanding of the formation mechanism of dual mycorrhizae.