New Insights into Leaf Physiological Responses to Ozone for Use in Crop Modelling

Abstract

Estimating food production under future air pollution and climate conditions in scenario analysis depends on accurately modelling ozone (O3) effects on yield. This study tests several assumptions that form part of published approaches for modelling O3 effects on photosynthesis and leaf duration against experimental data. In 2015 and 2016, two wheat cultivars were exposed in eight hemispherical glasshouses to O3 ranging from 22 to 57 ppb (24 h mean), with profiles ranging from raised background to high peak treatments. The stomatal O3 flux (Phytotoxic Ozone Dose, POD) to leaves was simulated using a multiplicative stomatal conductance model. Leaf senescence occurred earlier as average POD increased according to a linear relationship, and the two cultivars showed very different senescence responses. Negative effects of O3 on photosynthesis were only observed alongside O3-induced leaf senescence, suggesting that O3 does not impair photosynthesis in un-senesced flag leaves at the realistic O3 concentrations applied here. Accelerated senescence is therefore likely to be the dominant O3 effect influencing yield in most agricultural environments. POD was better than 24 h mean concentration and AOT40 (accumulated O3 exceeding 40 ppb, daylight hours) at predicting physiological response to O3, and flux also accounted for the difference in exposure resulting from peak and high background treatments.

Can Reduced Irrigation Mitigate Ozone Impacts on an Ozone-Sensitive African Wheat Variety?

“…By the end of the high O 3 exposure period, flag leaves in all irrigation treatments were significantly damaged and at various stage of senescence, resulting in different physiological responses to treatments compared to the healthy leaves at the start of the O 3 exposure period. Previous research indicated that accelerated senescence might be the dominant O 3 effect influencing wheat yield with O 3 effects on photosynthesis only observed alongside O 3 -induced leaf senescence, monitored as CCI [47]. However, the earlier significant decline in A sat compared to CCI in WW plants in the current study (resulting in a sometimes relatively high CCI compared to A sat at a CCI above 26 (Figure 4d)) suggests that a decline in photosynthesis might already occur before the onset of O 3 -induced leaf senescence.…”

“…Whilst ABA appears to play a central role in root-to-shoot chemical signalling to regulate growth and water use at reduced irrigation [36,37,38,39,40], elevated O 3 might reduce the sensitivity of stomatal closure to ABA in the presence of O 3 -induced emissions of ethylene [50,51,52]. Incomplete understanding of the physiological mechanisms driving O 3 -induced yield reduction hamper integration of O 3 effects in crop modelling [47,53,54]. It is not fully understood yet which processes affected by O 3 uptake at the leaf level are most important in driving ultimate yield loss.…”

“…It is not fully understood yet which processes affected by O 3 uptake at the leaf level are most important in driving ultimate yield loss. In crop modelling, there is a need to use a dynamic approach [47,55] and to improve the understanding of leaf-area dynamics in response to O 3 [54].…”

Effects of ozone on agriculture, forests and grasslands

“…This will occur either by directly impairing stomatal functioning (through damage to guard cells [128]) or indirectly through reductions in photosynthesis (caused by damage to photosynthetic machinery) leading to an increase in sub-stomatal CO 2 concentrations (Ci; #2) and closure of stomata [23]. Ozone may also reduce root:shoot biomass ratios [11] leading to reduced soil water uptake by roots (#8) and can accelerate leaf senescence (#7; [129], reducing plant water utilization. These effects will influence transpiration (#11; [130]) and have implications for C assimilation (#5), allocation (#6) and ultimately crop growth and yield [11].…”

Getting ready for the ozone battle: Vertically transmitted fungal endophytes have transgenerational positive effects in plants

“…Consequently, daily peaks of high ozone concentration usually occur around noon (Ainsworth et al, 2020, and references therein). By entering the plant through leaf stomata, and reacting with cellular components, oxidative stress rises as reactive oxygen species (ROS) are formed (Abeli et al, 2017; Osborne et al, 2016; Osborne et al, 2019). Depending on the type of exposure (chronic/acute) and concentration (low/high), ozone‐driven dysfunctionalities at an individual level can be detected as reduced photosynthesis, early leaf senescence and, eventually, plant death (see Agathokleous, Kitao, & Calabrese, 2020; Ainsworth (2017); Ainsworth et al (2012); Ashmore (2005); Fiscus, Booker, and Burkey (2005); Fuhrer (2009); Osborne et al (2016)).…”