A Land surface C transfer model and numerical experiments on belowground C accumulation and its impact on vegetation C level

Ota, Masakazu  ; Nagai, Haruyasu  ; Koarashi, Jun   

A model simulating transport and exchange for C (or CO) in a land surface ecosystem was developed and the belowground C accumulation and its impact on vegetation C level at a hypothetical cultivated field was studied with the model through numerical experiments. The developed model involved physical CO transport in surface atmosphere and soil and physiological CO exchanges in leaves, and was incorporated into a dynamical model (SOLVEG-II) that calculates transport and exchange for heat, water and CO. The model was tested through a simulation of an existing-experiment on an acute exposure of grape-plants to CO. The calculated C amount in leaves agreed with the observations within a factor of 1.7. A hypothetical scenario used for the numerical experiments considered an annual C input into surface soil layers via C-enriched foliage or root litter under a continually-heightened atmospheric CO environment. The specific activity of C in the surface soil layers increased with time and eventually converged to a certain value several decades after the start of accumulation. At this equilibrium state, the increased belowground CO production enhanced the atmospheric CO level, and consequently CO uptake by vegetation increased to 1.1 folds of the control one calculated without belowground C accumulation. The model results also demonstrated that C accumulated in soil can retain an enhanced vegetation C level for at least several decades even after the end of accumulation.