Annual Variations of the 14C Content of Soil CO2

Abstract

A 6-year and a 2-year record of ¹⁴C measurements of soil CO₂ in two soils are presented and discussed. The annual ¹⁴C variation of soil CO₂ is controlled by the seasonally varying contribution of root respiration and of microbial decomposition of organic matter producing soil CO₂. The Δ¹⁴C soil CO₂ difference between summer and winter is ca 50‰ in a soil where turnover of organic matter is fast (τ = 2.5a) and ca 100‰ in a soil of slow turnover (τ = 60a). A simple model describing the movement and turnover of organic matter is derived, giving the depth distributions of organic carbon and of ¹⁴C. The model needs a subdivision of the carbon reservoir into at least two reservoirs with residence times of τ₁ = la and τ₂ = 100a, respectively, and with a vertical transfer velocity in the order of 0.6mm/a.