| Forest tress are often allied with soil microbes to cope with complex living environments.The mutualistic symbiosis between fungi and higher plants to form mycorrhiza,especially ectomycorrhizal fungi(ECM)is very common.With the continuous development and application of research methods,the ecological functions and species diversity of mycorrhizal fungi were gradually discovered.The formation of ECM can increase the absorption range of plant roots and activate the poorly soluble nutrients in the soil,thus showing the growth-promoting effect.There are many species of Quercus plants which are highly adaptable and versatile.ECM often formed in the roots of Quercus species.The results of artificial inoculation showed that the ECM fungi were mainly comprised of basidiomycetes,a few ascomycetes and lower fungi.However,at present,the research on the ECM of Quercus in China is based on the northern species,such as Quercus liaotungensis and Q.mongolica.There are few reports about the ECM of introduced or southern species in China.In this study,the ECM fungi associated with two southern oaks,Q.fabri and Q.acutissima,and eight introduced southern oaks,Q.macrocarpa,Q.virginiana,Q.michauxii,Q.nuttallii,Q.nigra,Q.lyrata,Q.shumardii and Q.coccine,were used to perform ECM investigation,morphological description,isolation and culture,and high-throughput sequencing analysis.The species diversity of ECM fungi and the dynamic succession of flora in different sampling periods were revealed.Based on this,a greenhouse inoculation test of a variety of ECM fungi was carried out to screen functional strains that could promote the growth and nutrient absorption of Quercus.The main findings are as follows:(1)Morphological characteristics of ECM fungiA survey of ECM fungi in nursery,plantation and wild populations revealed that the native or introduced Quercus exhibited well-developed ECM roots.The morphology of the ECM fungi of the annual seedlings of the nursery Quercus spp.was similar,without significant difference in structure and color.ECM is mainly white dichotomous and monopodial pyramidal branches,occasionally rod-shaped or irregular branches,indicating that there may be a lack of diversity of ECM fungi associated with genus in the nursery,or the ability of seedlings to recruit ECM fungi.In the 14-year-old plantation of Q.virginiana,all the examined ECM samples showed black,white,yellow,carmine and oyster white appearances.It is monopodial pyramidal,pinnate,dichotomous,rod-shaped,and irregular branching.The difference in external morphology and anatomical features is significant.Q.acutissima and Q.fabri mainly formed white coralloid and rod-shaped branches of ECM fungi,and the type of mantle is relatively simple.(2)Diversity,distribution and succession of Quercus-associated ECM fungiThirty-nine strains of pure ECM fungi were cultured by isolation and culture,and their genetic development was analyzed based on ITS and LSU gene fragments.The ECM fungi of the nursery Quercus seedlings are concentrated in the genus Clitopilus,Sistotrema and Scleroderma.Culturable ECM fungi were not isolated from wild Quercus spp..Amplicon-based high-throughput sequencing of fungi from root tips revealed that the mycorrhizal fungal groups were distributed in Boletales,Russulales,Thelephorales and Agaricales 5 orders in the Basidiomycota.Clear seasonal dynamics of ECM communities associated with Q.virginiana were found.Scleroderma was dominant in all samples but its abundance decreased sharply and subsequently maintained a stable level.In contrast,Russula was rare in first sampling time,but increased gradually.Tomentella didn’t change remarkably,with one exception of the second sampling time,when Tomentella was abundant and comparable to Scleroderma.This observation was consistent with the emergence of epigeous fruiting bodies of Scleroderma and Russula observed in the fields.In different sampling periods,the dynamics of ECM fungi community associated with Q.acutissima changed significantly.In March,mycorrhizal fungi were almost totally compromised of Boletales,while in August,Russula dominated.NMDS analysis revealed that the ECM fungal communities among the root tips samples from different sampling time differed greatly.The community structures of Q.fabri ECM fungi in different habitats were significantly different.The ECM fungi of the nursery Q.fabri are mainly comprised of Boletales.The wild Q.fabri-associated ECM are mainly concentrated in Agaricales and the dominant ECM fungi in the ten-year-old plantation are from Russulales.(3)Basic biological characteristics of ECM fungiIndole-3yl-acetic acid(IAA)and abscisic acid(ABA)production were determined in Clitopilus sp.,Sistotrema sp.and Atractiella rhizophila using HPLC-MS/MS approach.Most strains conceived the ability to produce IAA and/or ABA,but the patterns of production were quite different.In the nitrogen source utilization test,it was found that most strains were better at utilizing organic nitrogen,particularly bovine serum albumin(BSA)and glutamine(Glu).(4)Effects of ECM fungi on growth and nutrient absorption of QuercusPot experiment inoculation assay was conducted to evaluate the effects of various types of basidiomycetous root fungal symbionts on Quercus spp.seedling growth and nutrient absorption.Results indicated that these isolates showed plant growth promoting activities to varied degrees and a considerable ability to regulate root configuration after two months of inoculation.With regards to nutrient absorption,it was found that the total nitrogen contents in aboveground tissues were improved in inoculated Q.virginiana seedlings.The total phosphorus contents in seedlings were either positively or negatively affected.The total potassium contents in stems and leaves were significantly enhanced in all treatments.The effects of other inoculation combinations on the nutrient absorption of seedlings were not obvious,which was probably depending on the symbiotic types.Conclusively,this study suggests that both endophytic and ECM fungi are capable of imparting benefits to Quercus spp.growth and highlights the potential of further mycobiome-based seedling raising technology.Furthermore,our results provide a theoretical and technical basis for the development of high-quality seedlings associated with mycorrhizal fungi. |
