Influence of soil moisture on Alnus rubra ectomycorrhizal fungal community distribution throughout a growing season

Background/Question/Methods

A dearth of information surrounds ectomycorrhizal fungal (EM) ecology and the influences of EM species distribution in temperate forests. EM species distribution may be influenced by fungal host specificity, their ability to spatially disperse and colonize tree roots, and by soil characteristics. The objective of this study is to analyze the impact of seasonal soil conditions, primarily soil moisture, on the distribution of EM species associated with an 85 year-old Alnus rubra stand in western Washington. The study will determine 1) which EM species are present and their relative abundance; 2) if soil conditions explain variation of EM species abundance; and 3) whether EM species abundance changes over a growing season. One hundred and fifty root cores with soil variables (volumetric water content, total C and N, available P, pH), and Frankia nodule presence were collected May to September 2011. EM species were identified using morphological and DNA sequencing techniques. EM sporocaps were collected and sequenced to refine DNA matches of EM tips. Cluster analyses and non-metric multidimensional scaling (NMDS) ordinations visualized fungal groups. Fungal species that characterized clusters were determined using indicator species analyses. Soil variables were overlaid on NMDS plots to examine relationships to fungal groups.

Results/Conclusions

Twenty-two different species of 85-year-old A. rubra-associated EM fungi were identified, with most species belonging to the Naucoria and Tomentella genera. The most abundant species over the sampling period were a Cortinarius and Tomentella species and three different Naucoria species. Species varied in their relative abundance and location in the plot over the sampling period. Grouping of root cores of EM species abundance for each month, their respective indicator species, and soil variables explaining the groups varied throughout the sampling period. The distribution of the EM community in relation to soil conditions varied from species to species across the growing season. Results indicate that seasonal change in soil conditions influences A. rubra EM species abundance and distribution.