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

Technical Report · Mon Nov 17 00:00:00 EST 2014

DOI:https://doi.org/10.2172/1163911· OSTI ID:1163911

Resh, Sigrid C. ^[1]

---

1. Michigan Technological Univ., Houghton, MI (United States)

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 fungal 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.

• Research Organization: Michigan Technological Univ., Houghton, MI (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• DOE Contract Number: SC0006986
• OSTI ID: 1163911
• Report Number(s): DOE-MTU-0006986
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
wood decomposition
soil organic carbon
stable carbon isotopes
soil CO2 efflux
dissolved organic carbon
soil carbon stability