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Title: Interactive Effects of Climate Change and Decomposer Communities on the Stabilization of Wood-Derived Carbon Pools: Catalyst for a New Study

Globally, forest soils store ~two-thirds as much carbon (C) as the atmosphere. Although wood makes up the majority of forest biomass, the importance of wood contributions to soil C pools is unknown. Even with recent advances in the mechanistic understanding of soil processes, integrative studies tracing C input pathways and biological fluxes within and from soils are lacking. Therefore, our research objectives were to assess the impact of different fungal decay pathways (i.e., white-rot versus brown-rot)—in interaction with wood quality, soil temperature, wood location (i.e., soil surface and buried in mineral soil), and soil texture—on the transformation of woody material into soil CO2 efflux, dissolved organic carbon (DOC), and soil C pools. The use of 13C-depleted woody biomass harvested from the Rhinelander, WI free-air carbon dioxide enrichment (Aspen-FACE) experiment affords the unique opportunity to distinguish the wood-derived C from other soil C fluxes and pools. We established 168 treatment plots across six field sites (three sand and three loam textured soil). Treatment plots consisted of full-factorial design with the following treatments: 1. Wood chips from elevated CO2, elevated CO2 + O3, or ambient atmosphere AspenFACE treatments; 2. Inoculated with white rot (Bjerkandera adusta) or brown rot (Gloeophyllum sepiarium) pure fungalmore » cultures, or the original suite of endemic microbial community on the logs; and 3. Buried (15cm in soil as a proxy for coarse roots) or surface applied wood chips. We also created a warming treatment using open-topped, passive warming chambers on a subset of the above treatments. Control plots with no added wood (“no chip control”) were incorporated into the research design. Soils were sampled for initial δ13C values, CN concentrations, and bulk density. A subset of plots were instrumented with lysimeters for sampling soil water and temperature data loggers for measuring soil temperatures. To determine the early pathways of decomposition, we measured soil surface CO2 efflux, dissolved organic C (DOC), and DO13C approximately monthly over two growing seasons from a subsample of the research plots. To determine the portion of soil surface CO2 efflux attributable to wood-derived C, we used Keeling plot techniques to estimate the associated δ13C values of the soil CO2 efflux. We measured the δ13CO2 once during the peak of each growing season. Initial values for soil δ13C values and CN concentrations averaged across the six sites were -26.8‰ (standard error = 0.04), 2.46% (se = 0.11), and 0.15% (se = 0.01), respectively. The labeled wood chips from the Aspen FACE treatments had an average δ13C value of -39.5‰ (se 0.10). The >12 ‰ isotopic difference between the soil and wood chip δ13C values provides the basis for tracking the wood-derived C through the early stages of decomposition and subsequent storage in the soil. Across our six research sites, average soil surface CO2 efflux ranged from 1.04 to 2.00 g CO2 m-2 h-1 for the first two growing seasons. No wood chip controls had an average soil surface CO2 efflux of 0.67 g CO2 m-2 h-1 or about half of that of the wood chip treatment plots. Wood-derived CO2 efflux was higher for loam textured soils relative to sands (0.70 and 0.54 g CO2 m-2 h-1, respectively; p = 0.045)), for surface relative to buried wood chip treatments (0.92 and 0.39 g CO2 m-2 h-1, respectively; p < 0.001), for warmed relative to ambient temperature treatments (0.99 and 0.78 g CO2 m-2 h-1, respectively; 0.004), and for natural rot relative to brown and white rots (0.93, 0.82, and 0.78 g CO2 m-2 h-1, respectively; p = 0.068). Our first two growing seasons of soil surface CO2 efflux data show that wood chip location (i.e., surface vs. buried chip application) is very important, with surface chips loosing twice the wood-derived CO2. The DOC data support this trend for greater loss of ecosystem C from surface chips. This has strong implications for the importance of root and buried wood for ecosystem C retention. This strong chip location effect on wood-derived C loss was significantly modified by soil texture, soil temperature, decomposer communities, and wood quality as effected by potential future CO2 and O3 levels.« less
  1. Michigan Technological Univ., Houghton, MI (United States)
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Resource Type:
Technical Report
Research Org:
Michigan Technological Univ., Houghton, MI (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES wood decomposition; soil organic carbon; stable carbon isotopes; soil CO2 efflux; dissolved organic carbon; soil carbon stability