Abstract

Soil radiocarbon measurements can be used to estimate soil carbon turnover rates and inventories. A labile component of soil carbon has the potential to respond to perturbations such as CO2 fertilization, changing climate, and changing land use. Soil carbon has influenced past and present atmospheric CO2 levels and will influence future levels. A model is used to calculate the amount of additional carbon stored in soil because of CO2 fertilization.

Introduction

The Intergovernmental Panel on Climate Change estimates that doubling atmospheric CO2 over preindustrial levels will lead to a global-mean temperature increase of 1.5–4.5°C (e.g., Mitchell et al., 1990). Predicting when or if this doubling will occur requires an improved understanding of the global carbon cycle. One key question is the role of soil humus, which contains approximately 3 times the amount of carbon present in the preindustrial atmosphere. Scientists need to know if the soil carbon is labile or inert. If labile, soil carbon can respond to perturbations, either adding or removing atmospheric CO2. If inert, soil humus does not significantly influence atmospheric CO2 levels.

The purpose of this chapter is to show how soil radiocarbon measurements can be used to estimate soil carbon turnover times. The results presented here can be thought of as providing an example of what could be done on a biome-to-biome basis were more soil radiocarbon data available. Background material discusses the greenhouse effect, the global carbon cycle, and CO2 fertilization, which are linked with soil carbon turnover times.