Work

Leaf phenology determines the response of poplar genotypes to O 3 through mesophyll conductance

Year: 2025

Type: article

Abstract: SUMMARY Tropospheric ozone (O 3 ) is a phytotoxic air pollutant that impairs photosynthesis. The mechanisms of O 3 ‐induced reduction of mesophyll conductance ( g m ) are not clear. We investigated the interaction of O 3 and leaf age on g m by using structural equation modelling (SEM) for two poplar clones (I‐214 and Oxford) exposed to three O 3 levels (ambient air, AA; 1.5 × AA; 2.0 × AA) in a free‐air controlled experiment. Clone‐specific phenological responses to elevated O 3 were found: I‐214 showed a rapid leaf turnover and formed new productive leaves, whereas Oxford was more ‘conservative’ maintaining old or injured leaves. In the I‐214 clone with fast leaf turnover, g m was reduced due to increasing cell wall thickness in new leaves, a possible reaction to increase its resistance against O 3 damage. As I‐214 leaves aged, a decrease in the fraction of the mesophyll surface area unoccupied by chloroplasts was observed at 2.0 × AA prior to a reduction in photosynthesis. In the Oxford clone with slow leaf turnover, g m was mainly affected by physiological rather than structural factors: in particular, a marked reduction of g m caused by abscisic acid (ABA) was noticed. As photosynthesis is limited by diffusional barriers, O 3 effects on g m will be key for carbon sequestration modelling of O 3 pollution and climate change.

Source: The Plant Journal

DOI: 10.1111/tpj.70091