OOS 23-5 - Linking soil microbial community diversity and ecosystem function in developing postfire forests in Greater Yellowstone

Increasingly frequent and large high-severity fires are rapidly reshaping forest landscapes and increasing the extent of young ( <40 years) postfire forests throughout the West. Consequences for trees receive much attention, but the microbial communities that dominate ecosystem biodiversity and control vital ecosystem processes, such as biogeochemical transformations of critical plant nutrients, are vastly understudied. It is especially unclear whether there are consistent relationships between soil microbial community structure and forest ecosystem function, and what factors explain such patterns. We asked how soil microbial community composition relates to indicators of ecosystem function in developing postfire lodgepole pine (Pinus contorta var. latifolia) forests of Grand Teton National Park (Wyoming, USA). During July 2022, we sampled 9 stands (0.25-ha plots) that burned as stand-replacing fire, were located in the same environmental setting, and varied in time since fire (6, 22 and 34 years, n=3 per age class). We divided plots into quadrants, tallied lodgepole pine density in each quadrant, then measured tree size (basal diameter and diameter at breast height) and collected foliage from 8 trees per quadrant (n=32 trees per plot) to assess foliar nitrogen (N) and carbon (C) concentration. To characterize soil microbial community composition, we extracted and composited three mineral soil cores (2 cm diameter x 15 cm depth) per quadrant (n=4 per plot). Average lodgepole aboveground net primary production (ANPP) increased with time since fire (3.9, 8.9, and 23.7 Mg ha-1 yr-1, respectively). Indicators of nutrient status suggest available N declined with time since fire but may not inhibit growth in these developing stands. Foliar N concentration in composite (all-age) lodgepole pine needles averaged 1.58% in 6-year-old forests, 1.35% in 22-year-old forests, and 1.21% in 34-year-old forests. Soil microbial DNA has been extracted, and the 16S rRNA gene v4 for bacterial and ITS2 gene regions for fungal communities have been amplified using PCR. Total microbial richness, composition, and differential abundance will be linked with indices of forest ecosystem function across age classes. Understanding links between microbial communities and ecosystem function in young postfire forests is essential for elucidating nutrient cycling and stand development as increased fire activity transforms Western forest landscapes.