Fungal community dynamics and carbon mineralization in Populus tremuloides, Picea mariana, and Pinus banksiana coarse woody debris in two ecoregions of northern Ontario

Abstract

In Canadian silvicultural systems, intensifying biomass removal while harvesting for saw or pulpwood is presently the only economically feasible way of increasing biomass feedstocks. As a result, there is less slash and subsequently less coarse woody debris (CWD) pools in different decay stages over time. The impacts on saproxylic fungi and ecosystem functioning are not well understood. Fungi are the primary agents of CWD decay in forests, playing essential roles in nutrient cycling and carbon storage. We compared fungal biodiversity and CWD mineralization across 3 CWD species (Pinus banksiana, Populus tremuloides, and Picea mariana), 5 decay classes, and 2 ecoregions representing 3W and 3E Ontario. Fungal diversity metrics and community structure were examined via high-throughput sequencing of the ITS2 region. CWD pieces were incubated in a temperature controlled lab setting and C mineralization rates measured. Moisture content, density, and nutrient dynamics, including C, N, P, K, Ca, Mg, and Mn concentrations, C:N ratio, and N:P ratio of CWD were assessed. Fungal communities significantly differed among CWD species, decay class, and ecoregion and were primarily correlated with Ca, Mn, and K concentrations, density, and C:N ratio. Species richness and diversity peaked in 3W Ontario and in decay classes 4 and 5. We observed a shift from pathogenic, colonizer fungi to an increased abundance of wood decay fungi as decay class increased. Hardwood CWD had higher abundances of white rot fungi than softwood CWD. C mineralization was higher in hardwood CWD, increased with decay class, and was primarily influenced by P concentration and density. Data from this study will be used in developing forest management strategies to preserve biodiversity and monitor carbon flux in northern boreal forests, particularly under intensified-bioenergy production silvicultural systems.