The diversity of ectomycorrhizal fungi in a mature beech-maple forest: Influences of soil environment and vegetation

Background/Question/Methods

Many important forest trees form mutually beneficial associations with ectomycorrhizal fungi (ECM) that colonize plant roots. ECM can enhance plant nutrient acquisition, and increase resistance to pathogens and drought. The distribution and diversity of ECM may be controlled by soil environment and plant diversity. Human activities, including forest fragmentation, can alter forest soils, which may negatively impact the diversity and abundance of ECM. Such ECM losses could result in altered patterns of forest productivity and carbon and nutrient cycling. To better understand the effects of soil environment and vegetation on ECM, we examined their distribution in relation to soil environmental conditions and the spatial distribution of plant species in a mature beech-maple forest in Northeastern Ohio. A total of 120 soil cores were collected in June and September of 2006 to a depth of 5-cm. Soil was sorted from roots and reserved for analysis of soil pH, C, N and P. DNA was extracted from root tips recovered from soil samples and used to amplify the internal transcribed spacer (ITS) region of the rRNA gene which has taxonomic significance. PCR product was used to generate terminal restriction fragment length polymorphism (TRFLP) profiles that were used to determine the presence of mycorrhizas and their proportional abundance within each soil core.

Results/Conclusions

We detected at least 37 different mycorrhizal species types among the cores, representing 16 different genera. Nearly half of all species belonged to the genera Russula and Tomentella (24% and 22% of ECM species respectively). These genera were also among the most commonly encountered with at least one species of Russula found in 51% of cores and one species of Tomentella found in at least 43% of cores. Roots from within a core were colonized by an average of 4.9 species of fungi. We found that soil environment was significantly correlated with the distribution of fungal genera within the forest. The genus Tomentella was significantly and positively correlated with soil C and N content and with the presence of beech trees of the largest diameter class (>60-cm dbh). In contrast, the genus Boletus was negatively correlated with the presence of beech trees of the largest diameter class. These results suggest that the distribution of important ECM may be influenced by the soil environment, emphasizing the sensitivity of belowground communities to environmental change.