Harvard Forest On-Going Research Projects

Harvard Forest Research

EBIS-Ameriflux: Characterizing Organic Carbon Flux from Litter Sources to Mineral-Soil Sinks

Principal Investigator: Paul Hanson
Oak Ridge National Laboratory: Nov 01 2007 - Dec 01 2011:

Abstract:
This research provides quantitative data on the rate of C flux from litter sources to mineral soil sinks for United States eastern hardwood forests. These data are necessary for testing process-level hypotheses and judging the efficacy of soil C cycling models. We have been utilizing 14C-enriched material from local releases of radiocarbon resulting in whole-ecosystem isotopic label near Oak Ridge, Tennessee to study issues associated with the terrestrial soil carbon cycle. In 2004 and 2005, new atmospheric pulses of 14CO2 led to biological enrichment of additional plant material on the Oak Ridge Reservation (ORR). These 14C inputs bring the EBIS-Oak Ridge field-scale manipulations to a conclusion, but provide a new opportunity to deploy enriched materials for soil carbon cycle studies along a climatic gradient of AmeriFlux hardwood sites.

The EBIS-Oak Ridge observations supported conclusions that intra- and inter-annual soil carbon cycling in hardwood forest soils should be characterized as a two-compartment system where surface leaf-litter and belowground root turnover represent the primary carbon sources for organic-layer and mineral-soil carbon cycles, respectively. After 3-years of litter manipulation and 4 years of tracking, 14C-signatures of bulk organic horizons indicate the arrival of enriched litter into the humus (Oe/Oa) layer with a turnover time of ~9 years. Fractionation of soil C by soil microbes, size/aggregate- and density-based methods suggests that labile mineral-soil carbon is disproportionately affected by root rather than leaf litter inputs. EBIS-Oak Ridge experimental findings are being used to parameterize and refine existing carbon dynamics models (Daycent, RothC) and to build new models for the characterization of key process-level features of the soil C cycle applicable to eastern temperate forests in general.

We propose a new experimental plan designed to apply newly-collected 14C enriched leaf and root litter and humus to multiple AmeriFlux sites for the direct characterization of leaf litter, organic layer humus, and fine root litter C transfers to mineral-soil sinks over a range of climatic and biological conditions. The experimental data generated by the EBIS-AmeriFlux effort together with conclusions from the preceding EBIS-Oak Ridge study will provide a key contribution to databases on soil carbon cycling processes for use in evaluating the next generation of terrestrial carbon models. Those models are needed in the ongoing evaluation of terrestrial ecosystem’s role in the global carbon cycle. This proposed research will provide data for addressing DOE’s goal of understanding mechanisms controlling C flux, and for the improvement of models to be applied to policy discussions regarding the safe levels of greenhouse gases for the earth’s system.

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	Harvard Forest Research EBIS-Ameriflux: Characterizing Organic Carbon Flux from Litter Sources to Mineral-Soil Sinks Principal Investigator: Paul Hanson Oak Ridge National Laboratory: Nov 01 2007 - Dec 01 2011: Abstract: This research provides quantitative data on the rate of C flux from litter sources to mineral soil sinks for United States eastern hardwood forests. These data are necessary for testing process-level hypotheses and judging the efficacy of soil C cycling models. We have been utilizing 14C-enriched material from local releases of radiocarbon resulting in whole-ecosystem isotopic label near Oak Ridge, Tennessee to study issues associated with the terrestrial soil carbon cycle. In 2004 and 2005, new atmospheric pulses of 14CO2 led to biological enrichment of additional plant material on the Oak Ridge Reservation (ORR). These 14C inputs bring the EBIS-Oak Ridge field-scale manipulations to a conclusion, but provide a new opportunity to deploy enriched materials for soil carbon cycle studies along a climatic gradient of AmeriFlux hardwood sites. The EBIS-Oak Ridge observations supported conclusions that intra- and inter-annual soil carbon cycling in hardwood forest soils should be characterized as a two-compartment system where surface leaf-litter and belowground root turnover represent the primary carbon sources for organic-layer and mineral-soil carbon cycles, respectively. After 3-years of litter manipulation and 4 years of tracking, 14C-signatures of bulk organic horizons indicate the arrival of enriched litter into the humus (Oe/Oa) layer with a turnover time of ~9 years. Fractionation of soil C by soil microbes, size/aggregate- and density-based methods suggests that labile mineral-soil carbon is disproportionately affected by root rather than leaf litter inputs. EBIS-Oak Ridge experimental findings are being used to parameterize and refine existing carbon dynamics models (Daycent, RothC) and to build new models for the characterization of key process-level features of the soil C cycle applicable to eastern temperate forests in general. We propose a new experimental plan designed to apply newly-collected 14C enriched leaf and root litter and humus to multiple AmeriFlux sites for the direct characterization of leaf litter, organic layer humus, and fine root litter C transfers to mineral-soil sinks over a range of climatic and biological conditions. The experimental data generated by the EBIS-AmeriFlux effort together with conclusions from the preceding EBIS-Oak Ridge study will provide a key contribution to databases on soil carbon cycling processes for use in evaluating the next generation of terrestrial carbon models. Those models are needed in the ongoing evaluation of terrestrial ecosystem’s role in the global carbon cycle. This proposed research will provide data for addressing DOE’s goal of understanding mechanisms controlling C flux, and for the improvement of models to be applied to policy discussions regarding the safe levels of greenhouse gases for the earth’s system. :
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