Epidemiological derivation of flux-based critical levels for visible ozone injury in European forests
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ORIGINAL PAPER
Epidemiological derivation of flux‑based critical levels for visible ozone injury in European forests Pierre Sicard1 · Alessandra De Marco2 · Elisa Carrari3 · Laurence Dalstein‑Richier4 · Yasutomo Hoshika3 · Ovidiu Badea5 · Diana Pitar5 · Silvano Fares6 · Adriano Conte6 · Ionel Popa5 · Elena Paoletti3
Received: 16 June 2020 / Accepted: 10 July 2020 © Northeast Forestry University 2020
Abstract The European MOTTLES project set-up a newgeneration network for ozone ( O3) monitoring in 17 plots in France, Italy and Romania. These monitoring stations allowed: (1) estimating the accumulated exposure AOT40 and stomatal O3 fluxes (PODY) with an hourly threshold of uptake (Y) to represent the detoxification capacity of trees (POD1, with Y = 1 nmol O3 m−2 s−1 per leaf area); and (2) collecting data of forest-response indicators, i.e. crown defoliation and visible foliar O3-like injury over the time period 2017–2019. The soil water content was the most important parameter affecting crown defoliation and was a key factor affecting the severity of visible foliar O3-like injury on the dominant tree species in a plot. The soil water content is thus an essential parameter in the PODY estimation, particularly for water-limited environments. An assessment based on
stomatal flux-based standard and on real plant symptoms is more appropriated than the exposure-based method for protecting vegetation. From flux-effect relationships, we derived flux-based critical levels (CLef) for forest protection against visible foliar O 3-like injury. We recommend CLef of −2 5 and 12 mmol m POD1 for broadleaved species and conifers, respectively. Before using PODY as legislative standard in Europe, we recommend using the CLec for ≥ 25% of crown defoliation in a plot: 17,000 and 19,000 nmol mol−1 h AOT40 for conifers and broadleaved species, respectively.
Project funding: This work was supported by the LIFE financial instrument of the European Union in the framework of the MOTTLES project “Monitoring ozone injury for setting new critical levels” (LIFE15 ENV/IT/000183).
Surface ozone ( O3) is a major air quality issue worldwide (Sicard et al. 2013, 2016a, 2017, 2020) with harmful effects on forest trees (Sicard et al. 2016b; Mills et al. 2018; Feng et al. 2019). The adverse effects can be a reduction of leaf chlorophyll content (Dalstein et al. 2005), sluggishness or impairment of leaf stomata (Hoshika et al. 2015), visible foliar O3 injury (Calatayud and Cerveró 2007; Paoletti et al. 2009; Schaub et al. 2010; Sicard et al. 2016c; Moura et al. 2018), and a reduction of growth (Fares et al. 2013; Proietti et al. 2016; Braun et al. 2017; Cailleret et al. 2018). The O3 exposure metric AOT40, i.e. the cumulated exposure to O 3 hourly concentrations exceeding 40 nmol mol−1 over the daylight hours during the growing season, is recommended for the protection of vegetation by the European Council Directive 2008/50/EC. For forest protection, an exposurebased critical level of 5000 nmol mol−1 h AOT40 is recommended by UNECE (2010
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