Comparatively little is known about mechanisms of potential changes in plant stress tolerance under
e[CO2]. Defence metabolites such as antioxidants are, in part, directly linked to primary carbohydrate
mechanism and so potentially impacted by e[CO2].
It is unknown whether photoprotective and antioxidative
defence systems, key to plant stress tolerance, will be affected, and if so, whether the response
will be strengthened or weakened by e[CO2].
Better understanding of underlying principles is particularly important because it is virtually impossible to test all possible stress factor combinations with e[CO2] in realistic field settings.