The prediction of complex interactive effects
of rising concentrations of ozone and CO2on vegetation
will require robust models based on mechanistic understanding of how these two
gases affect photosynthesis. This paper describes the development of a model
of acute ozone exposure effects on wheat leaf photosynthesis, based on the
mechanism of reactive oxygen scavenging processes. Based on experimental data,
the dose of ozone to the leaf above a threshold flux, here termed the
effective ozone dose, was found to be linearly related to the decline in the
in vivo maximum rate of carboxylation. The proposed
mechanism is that ozone damage to the photosynthetic ap paratus will only
occur above a critical rate of ozone delivery.
By combining the model of the response of ribulose-1,5-bisphosphate-saturated
and limited photosynthesis to ozone exposure with both a mechanistic
biochemical model of leaf photosynthesis and a phenomenological model of
stomatal conductance, it was possible to investigate the degree of dependency
of ozone-induced stomatal closure on changes in the mesophyll. The stomatal
conductance of the model simulation compared well with the magnitude of
measured stomatal closure. The results indicate that the stomatal changes
caused by acute ozone exposure can be predicted from changes in the mesophyll
rather than directly on the stomata.
The findings that the effects of ozone on photosynthesis can be predicted by
an effective ozone dose to the leaf, and that the resulting reduction in
CO2 assimilation rate can, in turn, predict stomatal
closure, greatly simplifies modelling the effects of elevated concentrations
of ozone and CO2 on wheat photosynthesis. Future work
should determine whether the model can be adapted to predict chronic ozone
exposure effects on photosynthesis, and whether it can be applied to other
species by adjusting the values of threshold flux, related to the maximum
scavenging capacity within the leaf, and the ozone slope coefficient,
representing the inherent sensitivity of the photosynthetic apparatus to
ozone.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.