Developing Ozone Risk Assessment for Larch Species

Yasutomo Hoshika,Elena Paoletti,Tetsuto Sugai,Evgenios Agathokleous,Takayoshi Koike

doi:10.3389/ffgc.2020.00045

Yasutomo Hoshika, Elena Paoletti + Show 3 more

Open Access

https://doi.org/10.3389/ffgc.2020.00045

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Abstract

Ozone (O3) risk assessment for the protection of forests requires species-specific critical levels (CLs), based on either O3 concentrations (AOT40) or stomatal uptake (PODY) accumulation over the growing season. Larch (Larix sp.) is a genus with O3-susceptible species, widely distributed in the northern hemisphere and with global economic importance. We analyzed published and unpublished data of Japanese larch (L. kaempferi) and its hybrid F1 (L. gmelinii var. japonica × L. kaempferi) responses to O3 exposure for developing a parameterization of stomatal conductance model and estimating PODY-based CLs with two Y thresholds, i.e. 0 and 1 nmol m-2 s-1 PLA. In parallel, we estimated AOT40-based CLs. The results show that the AOT40-based CLs for a 2% and 4% biomass loss in Japanese larch were 5.79 and 11.59 ppm h, i.e. higher than in hybrid larch F1 (2.18 and 4.36 ppm h AOT40), suggesting a higher O3-susceptibility of the hybrid. However, the use of PODY reconciled the species-specific differences, because the CLs were similar; i.e. 9.40 and 12.00 mmol m-2 POD0 and 2.21 and 4.31 mmol m-2 POD1 in Japanese larch, vs. 10.44 and 12.38 mmol m-2 POD0 and 2.45 and 4.19 mmol m-2 POD1 in the hybrid, for 2% and 4% biomass loss, respectively. Overall, the CLs were lower than in other forest species, which suggests a relatively high susceptibility of these larches. These results will inform environmental policy-makers and modelers about larch susceptibility to O3.

Highlights

Tropospheric ozone (O3) is the most widespread phytotoxic air pollutant (Mills et al, 2018)
When AOT40 was applied, in particular, a higher slope was found for hybrid larch F1 than for Japanese larch (Figure 2)
The critical levels (CLs) calculated on the basis of these dose–response relationships were 2.7 times higher in Japanese larch than in its hybrid F1 when AOT40 was used, while PODY-based CLs were similar between the two species when using either no Y threshold or a Y threshold of 1 nmol m−2 s−1 projected leaf area (PLA) (Table 3)

Summary

Introduction

Tropospheric ozone (O3) is the most widespread phytotoxic air pollutant (Mills et al, 2018). Ozone has a strong oxidative capacity and may cause severe injury to forests (Paoletti, 2007; Li et al, 2017). One of the most common metrics is AOT40, that is, the accumulated exposure over an hourly threshold of 40 ppb during the growing season, there is a general consensus that the accumulated stomatal O3 flux – or phytotoxic ozone dose (POD) – is more biologically meaningful as it estimates the amount of O3 entering the plants through the stomata (Paoletti and Manning, 2007). A flux threshold Y below which O3 uptake is not expected to be injurious to plants has been postulated.

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