A land surface ¹⁴C transfer model and numerical experiments on belowground ¹⁴C accumulation and its impact on...

A model simulating transport and exchange for ¹⁴C (or ¹⁴CO₂) in a land surface ecosystem was developed and the belowground ¹⁴C accumulation and its impact on vegetation ¹⁴C accumulation at a hypothetical cultivated field were studied with the model through numerical experiments. The developed model involved physical ¹⁴CO₂ transport in surface atmosphere and soil and physiological ¹⁴CO₂ exchanges in leaves, and was incorporated into a dynamical model (SOLVEG-II) that calculates transport and exchange for heat, water and CO₂. The model was tested through a simulation of an existing-experiment on an acute exposure of grape plants to ¹⁴CO₂. The calculated ¹⁴C amount in leaves agreed with the observations within a factor of 1.7. A hypothetical scenario used for the numerical experiments considered an annual ¹⁴C input into surface soil layers via ¹⁴C-enriched foliage or root litter under a continually heightened atmospheric ¹⁴CO₂ concentration. The specific activity of ¹⁴C in the surface soil layers increased with time and several decades after the start of accumulation it eventually converged to eight times the initial specific activity. At this equilibrium state, the increased belowground ¹⁴CO₂ production enhanced the atmospheric ¹⁴CO₂ level and, consequently, ¹⁴CO₂ uptake by vegetation increased to 1.1 times the control calculated without belowground ¹⁴C accumulation. The model results also demonstrated that ¹⁴C accumulated in soil can maintain an enhanced vegetation ¹⁴C level for at least several decades even after the end of accumulation.