Abstract
In order to understand the effect of phytotoxic tropospheric ozone (O3) on terrestrial vegetation, we quantified the impact of current O3 concentration ([O3]) on net ecosystem production (NEP) when compared to the conditions of the pre-industrial era. We compared and tested linear mixed-effects models based on [O3] and stomatal O3 flux (Fsto). The managed ryegrass–clover (Lolium perenne and Trifolium pratense) mixture was grown on arable land in the Czech Republic, Central Europe. Values of [O3] and Fsto were measured and calculated based on resistance analogy, respectively, while NEP was calculated from eddy covariance CO2 fluxes. We found the Fsto-based model more precise when compared to measured NEP. High Fsto was found even at low [O3], while broad summer maximum of [O3] was not necessarily followed by significant NEP decline, due to low soil water content leading to a low stomatal conductivity and Fsto. Comparing to low pre-industrial O3 conditions, current levels of O3 resulted in the reduction of cumulative NEP over the entire growing season, up to 29.7 and 13.5% when the [O3]-based and Fsto-based model was applied, respectively. During the growing season, an O3-induced reduction of NEP ranged between 13.1% in May and 26.2% in July when compared to pre-industrial Fsto levels. Looking to the future, high [O3] and Fsto may lead to the reduction of current NEP by approximately 13.3% on average during the growing season, but may increase by up to 61–86.6% in autumn, indicating further O3-induced acceleration of the senescence. These findings indicate the importance of Fsto and its inclusion into the models estimating O3 effects on terrestrial vegetation. The interaction between environmental factors and stomatal conductance is therefore discussed in detail.
Highlights
Tropospheric ozone (O3) is formed in UV-driven photochemical reactions from NO2, which are further catalyzed by precursor gases, including carbon monoxide, methane, and volatile organic compounds [1,2]
We quantified the reductions in net ecosystem production (NEP) of a managed ryegrass–clover mixture caused by current O3 conditions compared to pre-industrial O3 conditions and we predicted these reductions under expected future O3 conditions
Reductions of NEP were estimated by a linear mixed-effects model based on O3 concentration ([O3]) and stomatal O3 flux (Fsto)
Summary
Tropospheric ozone (O3) is formed in UV-driven photochemical reactions from NO2, which are further catalyzed by precursor gases, including carbon monoxide, methane, and volatile organic compounds [1,2]. Background [O3] usually reaches maxima during summer and in the mid-afternoon, respectively, while the minima occur during winter and night periods [3,6]. Such seasonal and diurnal patterns in [O3] are attributed to meteorological factors, solar radiation, temperature, and the availability of O3 precursors [2]. High [O3] results in the formation of reactive oxygen species (ROS) in leaf tissues, resulting in local necrotic cell death or early senescence [11], chloroplast injuries and an enlargement of intercellular spaces [12], coupled with a reduction of Rubisco content and a consequent decrease in photosynthetic CO2 uptake [13,14]. The diversity of response patterns to O3 occurs due to differences in stomatal conductivity to O3 [15], the genetically based potential to detoxify ROS [16], the species-specific plasticity to reallocate resources from damaged leaves [17], and the interaction of O3 with other environmental factors [2]
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