Diversity Maintenance Mechanism Of Ectomycorrhizal Fungal Community Associated With Pinus Tabuliformis In North China

Ectomycorrhizal(ECM)symbioses formed between special groups of soil fungi and fine root system of higher plant,which can promote the absorption of water and nutrients,and improve the resistance of host plants,effectively.Pinus tabuliformis is a typical ECM coniferous tree,and widely distributed in temperate forests of northern China.Because of strong adaptability and developed ECM system,P.tabuliformis is one of the most important afforesting tree species in the dry and semi-arid region of China,which is of great significance to the remediation of disturbed ecosystem and the development of regional economy of northern China.In this study,we investigated the diversity and composition of ECM fungal communities associated with P.tabuliformis by combining morphological classification with molecular identification to research the diversity of ECM fungi.Furthermore,according to the distribution characteristics of P.tabuliformis,it is divided into four geographical regions with distinct spatial and environmental heterogeneity,including eastern region,central region,southern region and northwest region.We analyzed the regional differentiation of ECM fungal communities associated with P.tabuliformis by comparing some community indicators,such as species diversity index,dominant species(genus),shared-endemic species,indicator species and community composition.And then,we analyzed the dominated factors that determine the diversity and composition of ECM fungal communities at the overall and regional scales.In addition,we also analyzed the relative importance of dispersal and selection processes on ECM fungal communities.The main research contents and results are as follows:1.A total of 331 ECM fungi operational taxonomic units(OTUs)were identified from330 samples collected from 66 plots,and 262 belonged to Basidiomycota,69 belonged to Ascomycota.Chao2 richness index showed that there are ca.496 fungi species can form ECM symbioses with P.tabuliformis in nature.Tomentella、Cenococcum、Sebacina、Russula、Inocybe and Amphinema were the dominant genera in ECM fungal communities and 153 singletons were existed,which indicates that the ECM fungal community of P.tabuliformis was composed of a small number of dominant groups and a large number of rare species.Cenococcum geophilum was the most important species because it has highest importance value.2.There was a significant difference in alpha diversity between the four geographic regions.ECM fungal richness in the eastern region was significantly lower than other three regions.Chao2 richness index in southern and central regions were significantly higher than the eastern and northwest region.Shannon index,Simpson index and Pielou index in central,southern and northwest regions were significantly higher than the eastern region.The most important species(highest importance value)in eastern,central,southern,northwest regions were Clavulicium sp.1,Amphinema sp.1,C.geophilum 2 and C.geophilum 1,respectively,showed that the dominant species in each geographic region were various.The results of shared-endemic species analyses showed that there were up to 257OTUs(77.6% of the total)exist only in a single geographic distribution region,and just five OTUs could be detected at four regions,simultaneously.Indicator species analysis showed that the number of indicator species in eastern,central,southern and northwest regions were 2,5,7 and 8.Sorensen and Jaccard similarity index of ECM fungi community in central and northwest region were higher,but central and southern region were lowest.Non-metric multidimensional scaling(NMDS)and permutational multivariate analysis of variance(PERMANOVA)showed there was significant difference in ECM fungal community composition between each regions.3.At whole distribution range scale,unit regression analysis showed that ECM fungal richness had significant correlation with longitude,latitude,altitude,pH,electrical conductivity(EC),organic matter(SOM),total phosphorus(TP)and total nitrogen(TN).Multiple stepwise regression analysis showed that latitude,pH,TN and EC were the main determinant of ECM fungi richness with an independent effects strength latitude > pH > TN >EC.At each geographic region scale,the distribution patterns and determinants of ECM fungi diversity were different.Mean annual precipitation(MAP)and pH were the main determinants of ECM fungal richness in central and eastern region,respectively.Latitude,altitude,EC,mean annual temperature(MAT)and MAP were the main factors that influence ECM fungi richness in the northwest region,and the impact strength were EC > altitude >MAT >latitude > MAP.25 ECM fungal genera had significant correlation with one or more environmental variables.Canonical correspondence analysis showed that Clavulicium and Clavulina genusECM fungi had prefer growth in low altitude area,Geopora,Choiromyces,Wilcoxina and Tricholoma were more suitable for habitat in arid,low temperature and high pH environments.Amphinema,Tuber,Suillus and Tomentella had no obvious environmental bias.4.At whole distribution range scale,Mantel test showed that ECM fungal community composition have significant correlation with geographical distance,MAT,MAP,altitude,pH,EC,SOM,TN,TP and carbon and nitrogen ratio(C/N).Multiple regressions on distance matrices(MRM)revealed ECM fungi community composition co-determined by geographic distance(6.8%),MAP(4.5%),pH(9.8%)and TN(1.5%),which illustrated ECM fungi community composition restricted by dispersal limitation and environmental selection,and environment selection act as the first-order determinants.However,at each geographic region scale,we found ECM fungal community composition was structured by dispersal limitation and environmental selection in central,southern and northwest region,but by only environmental selection in eastern region.