||extra carbon taken from the atmosphere under elevated atmospheric [CO2] and the fate of this extra carbon in terms of partitioning to, and residence time in carbon pools of different longevity. In Phase I (FY’10) we will improve understanding of the effect of spatial variation in nitrogen availability (both native and imposed) and temporal variation in climate (specifically in temperature, growing season length, and soil moisture) on the quantity of the extra carbon fixed under elevated CO2 and its allocation among pools of differing longevity. In Phase II (FY’11), harvesting above and below ground in half of each plot will constrain allometric responses and estimates of C in all pools. In Phase III (FY’11-’12) post-fumigation “relaxation” will be followed to separate direct from indirect effects of [CO2]; infrastructure removal will be a part of this phase.
Description: The Duke FACE experiment increases atmospheric [CO2] to a height of 25 m in four 30-m diameter plots, each containing ~100 canopy trees and many sub-canopy individuals, keeping the volume otherwise unaltered. The experiment began in 1994 with the prototype, and in three additional plots in 1996, enriching the atmosphere by 200 ppmv (e-[CO2]) relative to paired, comparable ambient plot (a-[CO2]).
The stimulation of NPP by e-[CO2] at Duke FACE has large spatial variation, and the partitioning of NPP among pools of different mean-residence times is even more variable, most likely owing to variation in nitrogen (N) availability. In March of 2005, FACE plots were split and fertilized, thus establishing a [CO2] X N study. Given pine needle longevity, and the slowness of large forests (i.e., ~22 m in height) to respond, the first responses to this mid-course adjustment of the experiment was observed in 2007 and 2008. Continuing enrichment through the growing season of 2010 will ensure an increased definition of the response (Phase I). Subsequent phases will reduce uncertainties in the estimated responses and allow separation of direct from indirect, long term structural effects. We will (1) determine the effect of N availability on the rate of C uptake, allocation and storage among the experimental 12 plots that span a well characterized gradient in soil-N availability, (2) test conceptual and quantitative models of C cycling under elevated CO2 and varying levels of N supply against the data collected from the N-fertilized portion of each FACE plot, (3) incorporate the effects of inter-annual variability in climate on C uptake, allocation and storage under e-[CO2] and varying levels of N availability.
The proposed research significantly expands the scope of inference by explicitly quantifying the effect of three global changes (CO2, N deposition, climate) on C storage in forests, and helping adjust the structure of models to account for these interactions, an ongoing joint activity with ORNL FACE.
Duration and Cost: Continuing CO2 enrichment through 2010 will provide the data necessary to assess a more stable response to the new [CO2] X N experiment. The following two years will be dedicated to a harvest immediately (to be completed by May 2011 to avoid growth under un-enriched conditions), a full year of monitoring followed by half a year of data synthesis and infrastructure removal. The 3-yr budget (Oct. 1, 2009 – Sept. 30, 2012) for (1) core science through Duke University is $2,618,652 ($901,471, $1,068,636, and $648,545 for the three years sequentially), (2) Operation—to be directed to Brookhaven National Lab is $3,444,000 ($1,798,000, $637,000, $1,009,000), and thus for (3) the entire experiment, the cost is $6,062,652 (FY’10: $2,699,471, FY’11: $1,705,636, FY’12:$1,657,545).
The long-term performance measure (LTM) of the proposed research is the delivery of data, parameters and functions to the modeling community. These deliverables will be used to calibrate and test prognostic models. The calibrated models will then be used to scale plot-level results from the Duke FACE site (and a companion study on sweetgum at ORNL FACE) to regional estimates of C sequestration with rising concentrations of atmospheric [CO2], a changing climate, and changing soil resource availability.