Change in net primary production and heterotrophic respiration: How much is necessary to sustain the terrestrial carbon sink?
In recent years, the chief approaches used to describe the terrestrial carbon sink have been either (1) inferential, based on changes in the carbon content of the atmosphere and other elements of the global carbon cycle, or (2) mechanistic, applying our knowledge of terrestrial ecology to ecosystem scale processes. In this study, the two approaches are integrated by determining the change in terrestrial properties necessary to match inferred change in terrestrial carbon storage. In addition, a useful mathematical framework is developed for understanding the important features of the terrestrial carbon sink. The Carnegie‐Ames‐Stanford Approach (CASA) biosphere model, a terrestrial carbon cycle model that uses a calibrated, semimechanistic net primary production model and a mechanistic plant and soil carbon turnover model, is employed to explore carbon turnover dynamics in terms of the specific features of terrestrial ecosystems that are most important for the potential development of a carbon sink and to determine the variation in net primary production (NPP) necessary to satisfy various carbon sink estimates. Given the existence of a stimulatory mechanism acting on terrestrial NPP, net ecosystem uptake is expected to be largest where NPP is high and the turnover of carbon through plants and the soil is slow. In addition, it was found that (1) long‐term, climate‐induced change in heterotrophic respiration is not as important in determining long‐term carbon exchange as is change in NPP and (2) the terrestrial carbon sink rate is determined not by the cumulative increase in production over some pre‐industrial baseline, but rather by the rate of increase in production over the industrial period.
© 1996 American Geophysical Union. (Received February 1, 1996; revised May 29, 1996; accepted May 29, 1996.) Paper Number 96GB01667. This research was funded in part by a NASA EOS/IDS grant to P. J. Sellers and H. A. Mooney and support from the Andrew W. Mellon Foundation to the Carnegie Institution of Washington. J.T.R. is supported on a NASA Global Change Fellowship. C.M.M. is supported on a DOE Global Change Fellowship. We thank Anne Ruimy for helpful review of the manuscript and Geeske Joel for critique of the figures. Special thanks to Franz-W. Badeck, who provided the live biomass turnover time data, and to Graham Farquhar, whose visit inspired this study. The complete model (in C with UNIX C shell scripts and documentation) is available upon request. This is CIW-DPB Publication number 1301.
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