Integrating O₃ influences on terrestrial processes: Photosynthetic and stomatal response data available for regional and global modeling

Using data from the peer-reviewed literature, we have compiled photosynthetic and stomatal responses to chronic O₃ exposure for all plant types with data available in the peer-reviewed literature as a standardized function of cumulative uptake of O₃ (CUO), which integrates O₃ flux into leaves through time. These data suggest that stomatal conductance decreases ∼11% after chronic O₃ exposure, while photosynthesis independently decreases ∼21%.

Despite the overall decrease in both variables, high variance masked any correlations between the decline in photosynthesis or stomatal conductance with increases in CUO. Though correlations with CUO are not easily generalized, existing correlations demonstrate that photosynthesis tends to be weakly but negatively correlated with CUO while stomatal conductance is more often positively correlated with CUO. Results suggest that large-scale models using data with strong negative correlations that only affect photosynthesis need to reconsider the generality of their response.

Data from this analysis are now available to the scientific community and can be incorporated into global models to improve estimates of photosynthesis, global land-carbon sinks, hydrology, and indirect radiative forcing that are influenced by chronic O₃ exposure.