Technical note: A simple theoretical model framework to describe plant stomatal “sluggishness” in response to elevated ozone concentrations

Abstract

Abstract. Elevated levels of tropospheric ozone, O3, cause damage to terrestrial vegetation, affecting leaf stomatal functioning and reducing photosynthesis. Climatic impacts under future raised atmospheric greenhouse gas (GHG) concentrations will also impact on the net primary productivity (NPP) of vegetation, which might for instance alter viability of some crops. Together, ozone damage and climate change may adjust the current ability of terrestrial vegetation to offset a significant fraction of carbon dioxide (CO2) emissions. Climate impacts on the land surface are well studied, but arguably large-scale modelling of raised surface level O3 effects is less advanced. To date most models representing ozone damage use either O3 concentration or, more recently, flux-uptake-related reduction of stomatal opening, estimating suppressed land–atmosphere water and CO2 fluxes. However there is evidence that, for some species, O3 damage can also cause an inertial “sluggishness” of stomatal response to changing surface meteorological conditions. In some circumstances (e.g. droughts), this loss of stomata control can cause them to be more open than without ozone interference. To both aid model development and provide empiricists with a system on to which measurements can be mapped, we present a parameter-sparse framework specifically designed to capture sluggishness. This contains a single time-delay parameter τO3, characterizing the timescale for stomata to catch up with the level of opening they would have without damage. The larger the value of this parameter, the more sluggish the modelled stomatal response. Through variation of τO3, we find it is possible to have qualitatively similar responses to factorial experiments with and without raised O3, when comparing to reported measurement time series presented in the literature. This low-parameter approach lends itself to the inclusion of ozone-induced inertial effects being incorporated in the terrestrial vegetation component of Earth system models (ESMs).

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“…When the O3 flux into plant stomata is small, plants naturally detoxify the oxidative stress from O3, but large O3 flux overwhelms the detoxification capacity and may cause visible foliage injury. Stomata can close, or in some cases become "sluggish" in responding to environmental changes (e.g., Huntingford et al, 2018), as a result of O3 damage, with ramifications to boundary-layer meteorology, water and carbon cycle, crop production and food security. In particular, it reduces gross primary production (GPP), which is the gross carbon uptake via photosynthesis and a measure of ecosystem productivity.…”

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“…Tropospheric ozone (O 3 ) is a toxic air pollutant with detrimental effects on vegetation (Yue and Unger, 2014;Juráň et al, 2021). Plant stomatal uptake of O 3 decreases both chlorophyll and Rubisco contents and increases the deformity rate of chloroplasts (Booker et al, 2007;Akhtar et al, 2010;Inada et al, 2012), which further reduces the leaf area index (LAI) and gross primary productivity (GPP) of ecosystems (Karnosky et al, 2007;Ainsworth et al, 2012). Modeling studies estimated that O 3 damage reduces global GPP by 1.5 %-3.6 % with regional maximum reductions of 8 %-20 % over eastern US, western Europe, and eastern China (Yue and Unger, 2014;Lei et al, 2020;Zhu et al, 2021).…”

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“…This is compounded by the fact that there is a need to incorporate within-plant feedbacks (e.g. sluggish stomatal responses) (Huntingford et al 2018) (see also…”