Mixedwood conifer trial to compare ectomycorrhizal and arbuscular fungal effects on soil organic matter decay

The purportedly enhanced decay of soil organic matter (SOM) by ectomycorrhizal fungi (EMF), in contrast to arbuscular mycorrhiza (AMF), was tested in a 30-year old mixedwood trial. Total peroxidase activity, including manganese-peroxidase (MnP), and mass of the humus layer were compared between Pseudotsuga menziesii (EMF) and Thuja plicata (AMF) across a natural productivity gradient. We found total peroxidase and MnP activity diverged between hosts as humus C:N increased, culminating in 3- to 4-fold greater enzyme activity for EMF on low fertility soils. This edaphic effect also correlated significantly with exchangeable Mn, highlighting a possible further restriction on SOM turnover by EMF. Peroxidase activity was well aligned with EMF species other than Cortinariaceae, notably Piloderma olivaceum and Piloderma sphaerosporum. The 3-fold decline in humus mass with decreasing soil fertility under P. menziesii, unlike T. plicata, was strong affirmation that EMF engaged in organic N liberation can lead to reductions in SOMcarbon sequestration