Current and future impacts of drought and ozone stress on Northern Hemisphere forests

Abstract

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Combined Acute Ozone and Water Stress Alters the Quantitative Relationships between O3 Uptake, Photosynthetic Characteristics and Volatile Emissions in Brassica nigra

“…Yet, only a few studies have investigated the impact of combined drought and ozone stresses and simultaneously monitored both photosynthetic and VOC emission characteristics [ 26 ]. Although both drought and O 3 reduce g s , O 3 can cause stomatal sluggishness, i.e., reduce the responsiveness of stomata to environmental clues such as light and humidity, disturbing the effective control of transpiration [ 44 ] and making the plants more vulnerable to the following stresses [ 45 ]. On the other hand, drought that precedes O 3 stress can reduce stomatal ozone uptake and thereby reduce O 3 -dependent damage [ 36 , 46 ], but whether the impact of drought on plant O 3 response is only due to reduced O 3 uptake or whether there is a significant interactive effect among drought and O 3 on photosynthesis and volatile emissions, e.g., due to drought priming, is not known.…”

FORCAsT‐gs: Importance of Stomatal Conductance Parameterization to Estimated Ozone Deposition Velocity

“…By introducing the Jarvis, Ball‐Berry and Medlyn parameterisations of stomatal conductance and photosynthesis into FORCAsT1.0, a 1‐D column model of trace gas exchange between a forest canopy and the atmosphere (Ashworth et al., 2015; Otu‐Larbi, Bolas, et al., 2020; Otu‐Larbi, Conte, et al., 2020), we were able to evaluate the performance of the three physiological models via comparison of simulated photosynthesis with long‐term measurements of GPP taken from the FLUXNET2015 data set (Pastorello et al., 2020). We find that all three models reproduce the seasonal and diel variations in GPP well at a range of forest types, Boreal evergreen (FI‐Hyy), Temperate deciduous (US‐Ha1), and Mediterranean evergreen (IT‐Cp2 and US‐Blo), but struggle to capture seasonality at a Tropical broadleaf evergreen site (BR‐Sa1).…”

“…The superior performance of the Medlyn optimisation model in the two Mediterranean climates could also be due to the fact that vegetation response to soil moisture stress is better accounted for through a combination of stomatal and biochemical limitations (e.g., see De Kauwe et al., 2015; Lin et al., 2015; Otu‐Larbi, Conte, et al., 2020). BB, by comparison, assumes that drought stress directly downregulates photosynthesis rates or is the result of biochemical limitation only (e.g., see Best et al., 2011; Clark et al., 2011; Fares et al., 2019).…”

“…The measured CO 2 from net ecosystem exchange (NEE) is partitioned into GPP and ecosystem respiration (Reco) using model parameterizations based on nighttime or daytime fluxes (Lasslop et al., 2010; Reichstein et al., 2005). We use GPP estimated from nighttime fluxes (GPP_NT_VUT_REF) for model evaluation as this is a standard benchmarking protocol in the land surface modeling community (see e.g., Harper et al., 2021; Otu‐Larbi, Conte, et al., 2020). In this study, GPP is assumed to be zero in the absence of light.…”

“…Ozone taken up through stomata is detrimental to plant growth and health leading to a decrease in productivity, causing billions of dollars in crop losses annually (Ainsworth et al., 2012; Avnery et al., 2011). Ozone damage has been shown to reduce gross primary productivity (GPP) by up to 10% in different forest ecosystems under current climatic conditions, although this impact is projected to decline in future as increased CO 2 and drought severity reduce stomatal conductance and hence stomatal ozone uptake (Oliver et al., 2018; Otu‐Larbi, Conte, et al., 2020).…”