Bryophyte diversity and soil organic carbon content in contrasting Northern Appalachian vernal pools

Bryophytes are important contributors to carbon (C) sequestration and play an important role in regulating C and nitrogen (N) flux in wetland environments. We assessed bryophyte species number and biomass, and select soil chemical parameters at four depth intervals (0–5, 5–10, 10–15, and 15–20 cm) in two vernal pool systems located within two contrasting physiographic provinces (the Appalachian Plateau and the Ridge and Valley) of the U.S. northern Appalachians. Results indicated that bryophyte species number and biomass were significantly higher in the Ridge and Valley versus the Appalachian Plateau system. While total soil organic carbon (TOC) and N were significantly higher in the Ridge and Valley at the shallower depths of 0–5, 5–10, and 10–15 cm, no significant differences were found between the two physiographic provinces for either parameter at the deepest depth interval (15–20 cm). The mineral-associated fraction of soil organic C, as indicated by the recalcitrant index for C (RIC), was only found to be significantly different at the 5–10 cm depth interval. When RIC was averaged across the samples for each study area, the mineral-associated fraction of soil organic C was found to be constant with depth in all vernal pools, while the relationship between RIC and TOC varied with depth within each vernal pool. These results suggest that variations in C input due to differing bryophyte species number and biomass may explain why vernal pools in the two contrasting study areas appear to have different TOC retention capacities, yet similar potentials for long-term C sequestration.