||Globally, soils contain twice as much carbon (C) as the atmosphere, with forest soils comprising about 17% of this soil C pool or 350 Pg of C (Amthor et al. 1998). The sequestration of soil organic carbon (SOC) is the residual between inputs from plant production and outputs from decomposition. In forested ecosystems, the dominant C inputs to the soil are derived from litter, woody debris, and roots. Increased wood removal for biofuel, among other uses, leads to the question, how important is wood (both above- and belowground sources) to soil C sequestration? Additionally, what mechanisms mediate SOC sequestration, particularly in the face of an altered climate predicted for the future? Woody biomass removals have the potential to affect the rate at which SOC is stored or lost, which could either attenuate or exacerbate increases in atmospheric CO2 (e.g., Schimel et al. 1990).
Our primary objectives directly investigate consequences of the expected future atmospheric chemistry (increased CO2 and O3) on the stabilization of woody biomass in terrestrial pools (soil C) versus being lost to atmospheric pools (CO2). Taking advantage of isotopically labeled wood, our overall research objectives are: 1. To determine the contribution of woody biomass produced under predicted future elevated levels of CO2 and O3 to stable SOC pools in forest soils, and 2. To assess the impact of different fungal decay pathways (i.e., white-rot versus brown-rot) in interaction with varying soil texture and soil temperature and initial contact with mineral fractions (i.e., buried versus surface wood) on the transformation of this woody material into long residence-time SOC components. In this exploratory research, we will accomplish three tasks: 1. Establish the experiment, 2. Characterize the initial transformation of the woody substrates, and 3. Test methods for SOC characterization as proof of concept for future funding. This research lays the foundation for a longer-term study tracking the fate of wood-derived C into distinct soil C pools.
In 2010, in Rhinelander, WI, the trees at the Aspen FACE (Free Air CO2 Enrichment) site were cut, providing large quantities of aspen woody biomass with unique 13C signatures (depleted by 14‰) and with biochemical characteristics altered by the treatments. The FACE wood was chipped and will be applied in a series of field decomposition experiments involving two soil types (coarse and fine textured), two types of integration (buried in the mineral soil vs. soil surface), two temperature treatments (warmed and ambient), three fungal inoculation treatments (white-rot, brown-rot, and natural rot), and three wood quality treatments (wood from +CO2, +CO2+O3, and ambient atmosphere). We will also include control plots with no added woody detritus.
To our knowledge, this study will represent the first field study directly investigating fungal priority effects on the ushering of wood-derived C into discrete soil fractions. As such, the results of this study will represent a true breakthrough in our understanding of controls on the transformation of biomass into long-lived SOC pools. Moreover, we will be able to directly measure changes in woody biomass pools, and the wood-derived C into SOC, with changes in climate (passive warming treatment).