Interactive effect of leaf age and ozone on mesophyll conductance in Siebold's beech

Abstract

Mesophyll conductance (Gm) is one of the most important factors determining photosynthesis. Tropospheric ozone (O3) is known to accelerate leaf senescence and causes a decline of photosynthetic activity in leaves. However, the effects of age‐related variation of O3 on Gm have not been well investigated, and we, therefore, analysed leaf gas exchange data in a free‐air O3 exposure experiment on Siebold's beech with two levels (ambient and elevated O3: 28 and 62 nmol mol−1 as daylight average, respectively). In addition, we examined whether O3‐induced changes on leaf morphology (leaf mass per area, leaf density and leaf thickness) may affect CO2 diffusion inside leaves. We found that O3 damaged the photosynthetic biochemistry progressively during the growing season. The Gm was associated with a reduced photosynthesis in O3‐fumigated Siebold's beech in August. The O3‐induced reduction of Gm was negatively correlated with leaf density, which was increased by elevated O3, suggesting that the reduction of Gm was accompanied by changes in the physical structure of mesophyll cells. On the other hand, in October, the O3‐induced decrease of Gm was diminished because Gm decreased due to leaf senescence regardless of O3 treatment. The reduction of photosynthesis in senescent leaves after O3 exposure was mainly due to a decrease of maximum carboxylation rate (Vcmax) and/or maximum electron transport rate (Jmax) rather than diffusive limitations to CO2 transport such as Gm. A leaf age×O3 interaction of photosynthetic response will be a key for modelling photosynthesis in O3‐polluted environments.

Integrating stomatal physiology and morphology: evolution of stomatal control and development of future crops

“…In the case of species such as Olea europaea occupying arid environments, where for extended periods water availability limits growth to a greater extent than the potential for photosynthetic CO 2 -uptake, minimising water-loss by largely restricting gas exchange to one surface may be advantageous (Guerfel et al 2007 ). Amphistomatous species may also be more vulnerable to infection via pathogenic fungi which enter the leaf through stomata (Muir 2015 ) and higher stomatal conductance is associated with increased entry of toxic atmospheric gases (Hoshika et al 2020 ). The majority of amphistomatous species have equal distributions of stomata on the abaxial and adaxial surfaces (so-called ‘perfect’ amphistomaty), suggesting that the selective pressures acting on stomatal distribution tend to strongly favour either ‘optimal outcomes’ of amphistomaty or hypostomaty with little evolutionary benefit for partial amphistomaty (Muir 2015 ).…”

Acclimation of mesophyll conductance and anatomy to light during leaf aging in Arabidopsis thaliana

“…On the other side, the scarce studies investigating how the leaf internal architecture modulates g m during leaf development and aging demonstrate that g m can be a significant constraint to photosynthesis during leaf life span (Clarke et al, 2021; Hanba et al, 2001; Hoshika et al, 2020; Marchi et al, 2008; Miyazawa et al, 2003; Miyazawa & Terashima, 2001; Niinemets et al, 2012; Tosens et al, 2012). Once fully expanded leaves achieve maximum g m , this photosynthetic trait tends to decrease with leaf age (Loreto et al, 1994; Niinemets et al, 2012), being suggested by Miyazawa and Terashima (2001), Miyazawa et al (2003), Tosens et al (2012), and Sugiura et al (2020) to be mainly due to the accumulation of cell wall material, which results in thicker cell walls.…”

Responses of photosynthesis and long-term water use efficiency to ambient air pollution in urban roadside trees

“…This indicates that non-stomatal factors are more important constraints than the stomata for leaf photosynthesis of these three urban tree species under high levels of NO and NO 2 . The importance of non-stomatal limitations for the reduction in photosynthesis by an air pollutant, O 3 , has been reported for poplar and beech (Xu et al 2019;Hoshika et al 2020). For G. biloba, on the other hand, the reduction in the difference between non-stomatal and stomatal limitations at the high-pollution levels (Fig.…”

“…Although exogenous NO reduced leaf photosynthesis, NO has important roles in protection against the harmful effects of heavy metals (Procházková et al 2013). Another important air pollutant ozone (O 3 ) imposes signi cant negative effects on the leaf photosynthesis of trees (Xu et al 2019;Hoshika et al 2020). Although urban roadside trees are expected to improve air quality by capturing particulate air pollutants, such as PM2.5 (Grzędzicka 2018;Zhao et al 2018), PM2.5 potentially reduces the leaf photosynthesis of urban trees; the heavy pollution of PM2.5 reduced the photosynthesis of a crop, wheat, up to 87% in wheat-planted farmland (Gu et al 2018).…”

“…The photosynthetic response to environmental variables is regulated by both stomatal and non-stomatal limitations, in which non-stomatal limitations are related to the leaf mesophyll anatomy and photosynthetic biochemistry (Flexas et al 2012). Although the stomatal response has been expected as a key for the photosynthetic response to air pollution (Wittig et al 2007), recent studies reported that for poplar and beech, the decline in photosynthesis caused by the atmospheric pollutant O 3 is largely due to increased non-stomatal limitations (Xu et al 2019;Hoshika et al 2020). Further and more extensive studies are needed to clarify the species-speci c effect of air pollution on the photosynthesis of urban trees and its underlying mechanisms.…”