PARENT SESSION
Poster Session 32: Biogeochemistry
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Water-soluble organic carbon characteristics and fluxes along climate and stand productivity gradients in interior Alaskan soils.

Kane, Evan^*,1, Valentine, David¹, Michaelson, Gary², Fox, John¹, Ping, Chien-Lu^{1, 2}, ¹ University of Alaska, Fairbanks, AK, USA² University of Alaska, Palmer, AK, USA

ABSTRACT- Soil carbon (C) balance in boreal forests is the small residual of two much larger C fluxes, soil respiration and net primary production, and therefore small changes in C cycling can change the net C status of these systems from a sink to a source. Soil respiration increases with temperature and primary production (as aboveground and root inputs decompose), but exactly how these factors influence the pool of water soluble organic C (WSOC), which moves with the mass flow of water from upland boreal forest soils, is uncertain. To examine this, we measured WSOC concentration and composition in organic and surface mineral soils, as well as soil CO₂ efflux, along 4 replicate gradients in upland black spruce productivity and climate in interior Alaska. The proportions of relatively bioavailable organic fractions (hydrophilic organic matter and low molecular weight acids) were highest in WSOC from the colder, low-productivity stands whereas the more degraded products of microbial activity (fulvic acids) were highest in warmer, high-productivity stands. Concentrations of WSOC in organic and mineral horizons ranged from 4.9−22.7 g C m^-2 and from 1.4−8.4 g C m^-2, respectively. Fluxes of WSOC (determined from a simple water balance model) ranged from 7.1−29.7 g C m^-2 yr^-1. Empirically modeled annual soil CO₂ efflux ranged from 365−739 g C m^-2 yr^-1 and increased with WSOC flux (r = 0.80, p=0.01); both fluxes were higher in warmer, more productive stands. Although annual WSOC flux was proportionately small compared to total soil CO₂ efflux across all sites (2−6%), its relative contribution was highest in warmer, more productive stands. These data suggest that WSOC should be accounted for in order to accurately determine the sensitivity of boreal soil organic C balance to climate change.

Key words: DOC, Picea mariana, climate change, high latitude