The response of mesophyll conductance to ozone-induced oxidative stress is genotype-dependent in poplar

Abstract

The CO2 diffusion conductance within the leaf mesophyll (gm) is considered a major limiting factor of photosynthesis. However, the effects of the major secondary air pollutant ozone (O3) on gm have been poorly investigated. Eight genotypes of the economically important tree species Populus x canadensis Moench were exposed to 120 ppb O3 for 21 days. gm showed a genotype-dependent response to O3-induced oxidative stress and was a major limiting factor of the net assimilation rate (Anet), ahead of stomatal conductance to CO2 (gsc) and of the maximum carboxylation capacity of the Rubisco enzyme (Vcmax) in half of the tested genotypes. An increased leaf dry mass per area (LMA) and a decreased chlorophyll content were linked to the observed gm decrease, but this relationship did not entirely explain the different genotypic gm responses. Moreover, the oxidative stress defence metabolites ascorbate and glutathione were not related to O3-tolerance of gm. However, malondialdehyde (MDA) probably mitigated the observed gm decrease in some genotypes due to its oxidative stress signalling function. The large variation of gm suggests different regulation mechanisms amongst poplar genotypes under oxidative stress.

Variations in leaf anatomical characteristics drive the decrease of mesophyll conductance in poplar under elevated ozone

“…In this study, the contributions of g m to the decreased photosynthesis under elevated O 3 were most important, and there was no significant effect of O 3 on g s in clone “546” (Table 1; Xu et al, 2019). Contrastingly, decreased g s , but not g m , was the most important contributor to O 3 ‐induced declines in photosynthesis in the Populus × canadensis Moench genotype (Joffe et al, 2022). Thus, the contributions of g s , g m , and biochemical capacity to limiting photosynthesis under elevated O 3 may be species dependent.…”

“…However, conflicting relationships between LMA and g m under elevated O 3 have been reported. Recent studies have shown that the O 3 ‐induced reduction of g m is mainly due to increased LMA and leaf density (Hoshika et al, 2020; Joffe et al, 2022). Ozone‐induced thicker leaf density may be associated with increased cell wall thickness and decreased g m (Hoshika et al, 2020; Joffe et al, 2022).…”

“…Recent studies have shown that the O 3 ‐induced reduction of g m is mainly due to increased LMA and leaf density (Hoshika et al, 2020; Joffe et al, 2022). Ozone‐induced thicker leaf density may be associated with increased cell wall thickness and decreased g m (Hoshika et al, 2020; Joffe et al, 2022). However, the LMA and leaf density in the present study positively correlated with g m and T cw (Table 1 and Figure 5).…”

“…Stomatal conductance ( g s ), photosynthetic biochemical capacity, and mesophyll conductance ( g m ) are the three physiological factors that control photosynthesis (Farquhar et al, 1980; Flexas et al, 2016). Several studies have confirmed that O 3 ‐induced g m impairment is critical in limiting leaf photosynthesis (Hoshika et al, 2020; Joffe et al, 2022; Xu et al, 2019). However, the mechanism by which elevated O 3 affects g m has not yet been clarified.…”

“…limiting leaf photosynthesis (Hoshika et al, 2020;Joffe et al, 2022;Xu et al, 2019). However, the mechanism by which elevated O 3 affects g m has not yet been clarified.…”