Hubbard Brook Experimental Forest: soil, litter, plant and microbial attributes on mycorrhizae litter decomposition plots

Studies show mycorrhizal fungi can influence leaf litter decomposition in a variety of ways, but the effects of arbuscular mycorrhizal (AM) fungi and ectomycorrhizal (ECM) fungi on litter decay in forests vary widely across published reports. We experimentally reduced the presence of fine roots and their associated mycorrhizal fungi by soil trenching within a series of plots spanning a gradient of mycorrhizal dominance containing from 96% AM to 100% ECM-associated trees at Hubbard Brook Experimental Forest in Woodstock, NH. We incubated four species of leaf litter in mesh decomposition bags in areas with reduced access to roots and mycorrhizal fungi and in adjacent areas with intact roots and mycorrhizal fungi. After 608 days of decomposition (November 2017 through July 2019), we found that litter decayed more rapidly in the presence of fine roots and mycorrhizal hyphae in all plots, regardless of dominant tree mycorrhizal type. Root and mycorrhizal exclusion did not affect enzyme activities on decomposing litter or soil microbial community composition. Despite reports that both AM and ECM fungi may reduce litter decay rate, our results indicate that AM and ECM-associated fine roots stimulate litter decomposition.