Abstract:

Objective: Quercus virginiana (Fagaceae), native to the southeastern United States, is recently introduced to the Yangtze Delta and often planted as landscape and coastal shelter forests. Quercus root tips are often heavily colonized by a phylogenetic diverse group of ectomycorrhizal (ECM) fungi, which improve nutrient acquisition and stress resistance for host plants. The purpose of this work is thus to reveal the identities of ECM fungi associated with Q. virginiana roots in the new environment. Method: The ectomycorrhizal root samples were collected at four different stages from October 2017 to August 2018 and traditional morphological description, fungal amplicon-based high-throughput sequencing approaches were used to investigate the diversity and structure dynamics of ectomycorrhizal fungi associated with Q. virginiana. Result: All the examined ectomycorrhizas showed black, white, yellow, and their intermediate colors (carmine and oyster white) appearances. The presence of mantle structure was observed microscopically. Based on the operational taxonomic units (OTUs) assignment and their relative abundances, the first three colored mycorrhizas corresponded to the fungi belonging to Tomentella, Scleroderma, and Russula, respectively, which showed rich interspecific genetic diversity inferred from phylogenetic analysis. Weighted Pair-Groups Method Average (WPGMA) cluster analysis of the OTU data matrix revealed that fungal compositions of the remaining two colored-mycorrhizas were very similar to those presented in yellow and black-colored mycorrhizas, respectively, indicating the different development stage of the same type of ectomycorrhizas. In addition, a few other ectomycorrhizal taxa including Amanita, Hebeloma, Pisolithus, Lactarius, and Sebacinales were detected with low abundances. The ectomycorrhizal community structure varied obviously in different sampling time. It is mainly shown as follows:Scleroderma dominated in all samples, its abundance was high at the initial stage, and then gradually decreased and subsequently maintained a stable abundance level; On the contrary, Russula had very low proportion in first sampling time, but increased its abundance gradually; Tomentella was not changed remarkably, with one exception was the second sampling time, in which Tomentella was abundant and comparable to Scleroderma. This observation was also consistent with the emergence of epigeous fruiting bodies of Scleroderma and Russula observed in the field. The non-metric multidimensional scaling analysis revealed that there were obvious differences in the ectomycorrhizal fungal communities of the root tips samples from four sampling periods of time (stress=0.157). Highest α-diversity indices (Chao1, ACE, Shannon, and Simpson) were observed in the ectomycorrhizal fungal communities of pooled samples collected at the second sampling period. Also, the greatest pairwise dissimilarity value occurred between the samples from the first and fourth sampling period of time based on β-diversity heatmap. Conclusion: The ectomycorrhizal fungi associated with Q. virginiana are mainly composed of Tomentella, Scleroderma and Russula. There are significant changes of ectomycorrhizal fungal communities at different growth stages, which are probably correlated with the changes of soil moisture and temperature. The results also gain the highlights on exploiting ectomycorrhizal fungi for mycobiont-based Q. virginiana cultivation technology.

Key words: Scleroderma, Russula, Tomentella, amplicon-based high-throughput sequencing, symbiosis