Elevated CO2 differentiates ecosystem carbon processes: Deconvolution analysis of Duke Forest FACE data

Quantification of the flux of carbon (C) through different pathways is crit ical to predict the impact of global change on terrestrial ecosystems. Past research has encountered considerable difficulty in separating root exudat ion, root turnover rate, and other belowground C fluxes as affected by elev ated CO2. In this study we adopted a deconvolution analysis to differentiat e C flux pathways in forest soils and to quantify the flux through those pa thways. We first conducted forward analysis using a terrestrial-C sequestra tion (TCS) model to generate four alternative patterns of convolved respons es of soil surface respiration to a step increase in atmospheric CO2. The m odel was then validated against measured soil respiration at ambient CO2 be fore it was used to deconvolve the CO2 stimulation of soil respiration. Dec onvolved data from the Duke Forest free-air CO2 enrichment (FACE) experimen t suggest that fast C transfer processes, e.g., root exudation, are of mino r importance in the ecosystem C cycling in the Duke Forest and were not aff ected by elevated CO2. The analysis indicates that the fine-root turnover i s a major process adding C to the rhizosphere. This C has a residence time of several months to similar to2 yr and increases significantly with increa sed CO2, In addition, the observed phase shift in soil respiration caused b y elevated CO2 can be only reproduced by incorporation of a partial time de lay function in C fluxes into the model. This paper also provides a detaile d explanation of deconvolution analysis, since it is a relatively new resea rch technique in ecology.