Nitrous Oxide Emissions and Microbial Communities Associated with Mycorrhizal-Inoculated Willows.

Due to the ability of willow trees (Salix spp.) to thrive in contaminated, water-logged and low nutrient soils, they are increasingly used for remediation of marginal lands. Furthermore, their rapid production rates in short-rotation coppice systems have made them sources of biomass for use in biofuel production. Willows can be colonized by both arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi which can improve primary production in part through increased access to soil nutrients. By establishing a more efficient nutrient cycle in the rhizosphere, mycorrhizae may alter emission rates of the greenhouse gas nitrous oxide (N₂O). Due the role of willows in the biofuel industry, we wanted to examine how mycorrhizal fungi may impact the cycling of nitrogen in willow systems, particularly with respect to N₂O. A greenhouse experiment evaluated the effect of AM and EM inoculation on willow growth, microbial community dynamics, and emissions of N₂O. Cuttings from two willow genotypes (S. viminalis and S. miyabeana) were potted in 6 Southern Ontario soils representing a range of soil textures.  Cuttings were inoculated with commercial mycorrhizal fungal inoculant in 1 of 4 treatments: 1) AM (Glomus intraradices), 2) EM (Hebeloma cylindrosporum), 3) AM and EM, or 4) uninoculated. After 40 days, willow trees were placed in flow-through chambers for 72 hours to determine N₂O fluxes using tunable diode laser technology. N₂O emissions were found to be significantly influenced by soil type, plant presence and inoculation. After 4 months, trees were harvested and DNA was extracted from soil and root samples. Soil, genotype and mycorrhizal treatment all significantly affected above-ground biomass. Colonization and presence of nitrifying and denitrifying microorganisms was assessed by quantitative polymerase chain reaction (PCR). This research will contribute to an understanding of the link between rhizosphere microbial communities and N₂O emissions in a willow production system.