Poster #4

Pine encroachment into hardwood forests alters soil fungal communities with consequences for soil nutrient cycling
C. VIETORISZ, N. POLICELLI, C. TATSUMI, J.M. BHATNAGAR
Department of Biology, Boston University, 5 Cummington Mall, Boston, MA 02215

While the processes governing aboveground forest changes are well-studied, little is known about belowground processes driving and accompanying changes in tree composition. In the northeastern US, white pines encroach into hardwood forests, creating understories of young pines beneath hardwood canopies. We hypothesized that encroaching pines alter soil nutrient cycling by associating with ectomycorrhizal fungi (EMF) that mine soil N and P to meet their hosts’ nutrient demands. We assessed fungal communities, their transcriptomic activity, and soil biogeochemistry across four forest types in Massachusetts, USA: mature pine forests, mature hardwood forests, hardwood forests with encroaching pines, and mature mixed forests. We found a positive relationship between EMF relative abundances, N-decomposition gene copies from EMF, and net ammonification rates. The EMF-ammonification relationship is strongest under pine encroachment, suggesting that pine-associated EMF may be mining N at high rates to meet the demands of fast-growing pines. Net nitrification rates are significantly lowest under pine encroachment, which may be explained by the negative relationship between EMF abundance and net nitrification. Pine-associated EMF may be competing with nitrifying bacteria for ammonium, reducing nitrification rates. To determine the metabolic causes of these trends, we are conducting meta-transcriptomics on the soil fungal community.