Elevated Tropospheric Ozone Concentration Alters Soil Co2 Emission: A Meta-Analysis

Elevated tropospheric ozone (O-3) concentration may substantially influence the below-ground processes of terrestrial ecosystems. Nevertheless, a comprehensive and quantitative understanding of O-3 impacts on soil CO2 emission remains elusive, making the future sources or sinks of soil C uncertain. In this study, 77 pairs of observations (i.e., elevated O-3 concentration treatment versus control) extracted from 16 peer-reviewed studies were synthesized using meta-analysis. The results depicted that soil CO2 efflux was significantly reduced under short-term O-3 exposure (<= 1 year, p < 0.05), while it was increased under extended duration (>1 year, p < 0.05). Particularly, soil CO2 emission was stimulated in nonagricultural ecosystems, in the free-air CO2 enrichment (FACE) experiment, and in the soils of lower pH. The effect sizes of soil CO2 efflux were significantly positively correlated with experimental duration and were significantly negatively correlated with soil pH, respectively. The ozone effect on soil CO2 efflux would be enhanced at warm temperatures and high precipitation. The duration of O-3 exposure was the fundamental factor in analyzing O-3 impacts on soil CO2 emission.