The Impact of Elevated Atmospheric [CO2] on Soil C and N Dynamics: A Meta-Analysis

Abstract

The current rise in atmospheric [CO2], a consequence of human activities such as fossil fuel burning and deforestation, is thought to stimulate plant growth in many ecosystems (Bazzaz and Fajer 1990). Gifford (1994) suggested that the resulting increase in C assimilation by plants and its subsequent sequestration in the soil could counterbalance CO2 emissions. However, higher plant growth rates in a CO2-rich world can only be sustained if the soil supplies plants with additional nutrients (Zak et al. 2000; Luo et al. 2004). Therefore, the effect of elevated (e)[CO2] on soil N availability is of key importance when predicting the potential for C storage in terrestrial ecosystems. In short-term experiments, soil N availability can decrease (Diaz et al. 1993) or increase (Zak et al. 1993) under e[CO2], depending on the response of the soil microbial community. Moreover, plants under e[CO2] can increase N uptake at the expense of microbial N consumption (Hu et al. 2001). Clearly, the impact of higher [CO2] levels on C and N dynamics in terrestrial ecosystems depends on a set of complex interactions between soil and plants. Also, the establishment of equilibrium between soil organic matter (SOM) input and decomposition can take up to decades or longer. Therefore, we need longterm experiments under realistic field situations to predict changes in ecosystems under future [CO2]. The use of open-top chambers (OTC) and free-air carbon dioxide enrichment (FACE) techniques allowed for CO2 fumigation studies under far more realistic conditions than before (Rogers et al. 1983; Hendrey 1993; Chapter 2). Over the past two decades, many OTC and FACE experiments have been conducted, covering a wide range of terrestrial ecosystems. Soil characteristics