Ozone risk assessment in three oak species as affected by soil water availability

Abstract

To derive ozone (O) dose-response relationships for three European oak species (Quercus ilex, Quercus pubescens, and Quercus robur) under a range of soil water availability, an experiment was carried out with 2-year-old potted seedlings exposed to three levels of water availability in the soil and three levels of O pollution for one growing season in an ozone free-air controlled exposure (FACE) facility. Total biomass losses were estimated relative to a hypothetical clean air at the pre-industrial age, i.e., at 10 ppb as daily average (M24). A stomatal conductance model was parameterized with inputs from the three species for calculating the stomatal O flux. Exposure-based (M24, W126, and AOT40) and flux-based (phytotoxic O dose (POD)) dose-response relationships were estimated and critical levels (CL) were calculated for a 5% decline of total biomass. Results show that water availability can significantly affect O risk assessment. In fact, dose-response relationships calculated per individual species at each water availability level resulted in very different CLs and best metrics. In a simplified approach where species were aggregated on the basis of their O sensitivity, the best metric was POD, with a CL of 6.8 mmol m for the less O-sensitive species Q. ilex and Q. pubescens and of 3.5 mmol m for the more O-sensitive species Q. robur. The performance of POD, however, was very similar to that of POD, and thus a CL of 6.9 mmol m POD and 3.6 mmol m POD for the less and more O-sensitive oak species may be also recommended. These CLs can be applied to oak ecosystems at variable water availability in the soil. We conclude that POD is able to reconcile the effects of O and soil water availability on species-specific oak productivity.

A procedure to evaluate the factors determining the elemental composition of PM2.5. Case study: the Veneto region (northeastern Italy)

“…Hoshika et al (2017a) tested a ratio of photosynthesis to ozone uptake as an index for the assessment of foliar visible injury in Oxford poplar. The same team (Hoshika et al 2017b) investigated in a free-air controlled exposure facility the ozone doseresponse relationships for three European oak species under a range of soil water availability. Physiological and biochemical responses to long-term exposure to ozone of two Italian provenances of Fraxinus excelsior were the focus of the paper presented by Cotrozzi et al (2017a).…”

What Are the Principal Factors Affecting Ambient Ozone Concentrations in Czech Mountain Forests?

“…On a long-term basis, ambient O 3 has been considered as a stress factor contributing to impairment of forest health status and its influence has been studied from different aspects. In spite of clear evidence of O 3 harmful effects observed in laboratory experiments, fumigation chambers, or FO 3 X (Free air O 3 eXposure) experiments (Sandermann et al, 1997;Paoletti et al, 2017;Franz et al, 2018;Hoshika et al, 2018), the field evidence for impacts of O 3 exposure on tree growth is not that clear (De Vries et al, 2014;Cailleret et al, 2018). Moreover, observations in real stand conditions from numerous regions show that measured high O 3 exposures or modeled high O 3 stomatal flux do not correspond with unclear impacts on forest ecosystems (e.g., Ferretti et al, 2007;Matyssek et al, 2007;Waldner et al, 2007;Baumgarten et al, 2009).…”

Extrapolating plot-scale CO2 and ozone enrichment experimental results to novel conditions and scales using mechanistic modeling

“…In fact, several studies (McLaughlin et al 2007;Sun et al 2012) reported substantial increases of transpiration at the ecosystem-level in southeastern US forests that were attributed to ozone-induced stomatal sluggishness. This exacerbates the effect of drought because impaired stomata reduce the ability of trees to conserve water (Hoshika et al 2018a). In the Aspen FACE experiment, the stomatal CO 2 response of aspen-birch communities was inhibited by ozone and this effect developed progressively over the growing season (Onandia et al 2011).…”

“…As a result, ozone decreases intrinsic water use efficiency and thus increases C i (e.g., Farage and Long 1995). Using empirical measures of stomatal response to ozone and water stress in a different free-air ozone exposure experiment (Hoshika et al 2018a; see Paoletti et al 2017 for the detail of the experiment), we developed equations to modify C i (Cimodifier) as a function of cumulative ozone dose, water stress and species susceptibility to stomatal sluggishness in response to ozone, to reflect the effects of ozone on stomatal conductance:…”

“…Regression coefficients for computing the effects of ozone on stomatal sluggishness (Cimodifier) based on data fromHoshika et al (2018a, b) …”