Elsevier

Atmospheric Environment

Volume 45, Issue 28, September 2011, Pages 5064-5068
Atmospheric Environment

Short communication
New stomatal flux-based critical levels for ozone effects on vegetation

https://doi.org/10.1016/j.atmosenv.2011.06.009Get rights and content

Abstract

The critical levels for ozone effects on vegetation have been reviewed and revised by the LRTAP Convention. Eight new or revised critical levels based on the accumulated stomatal flux of ozone (PODY, the Phytotoxic Ozone Dose above a threshold flux of Y nmol m−2 PLA s−1, where PLA is the projected leaf area) have been agreed. For each receptor, data were combined from experiments conducted under naturally fluctuating environmental conditions in 2–4 countries, resulting in linear dose–response relationships with response variables specific to each receptor (r2 = 0.49–0.87, p < 0.001 for all). For crops, critical levels were derived for effects on wheat (grain yield, grain mass, and protein yield), potato (tuber yield) and tomato (fruit yield). For forest trees, critical levels were derived for effects on changes in annual increment in whole tree biomass for beech and birch, and Norway spruce. For (semi-)natural vegetation, the critical level for effects on productive and high conservation value perennial grasslands was based on effects on important component species of the genus Trifolium (clover species). These critical levels can be used to assess protection against the damaging effects of ozone on food security, important ecosystem services provided by forest trees (roundwood production, C sequestration, soil stability and flood prevention) and the vitality of pasture.

Section snippets

Introduction and background

Tropospheric or ground-level ozone pollution has increased significantly over the last 100 years (Vingarzan, 2004) with current and future effects on health, ecosystems and vegetation being of considerable concern (Royal Society, 2008). For example, a recent study indicated that in Europe over 30 crop and 80 (semi-)natural vegetation species growing in 16 countries showed visible injury symptoms and other negative effects of ambient ozone such as biomass/yield reduction in the period of

The stomatal flux model used for the flux-based critical levels

Stomatal flux of ozone for an upper canopy sun-lit leaf is modelled using a multiplicative algorithm adapted from Emberson et al. (2000a) that incorporates the effects of air temperature (ftemp), vapour pressure deficit of the air surrounding the leaves (fVPD), light (flight), soil water potential (fSWP) or plant available water content (fPAW), plant phenology (fphen) and ozone concentration (fozone) on the maximum stomatal conductance (gmax, mmol O3 m−2 PLA s−1), i.e. the stomatal conductance

Agricultural crops

The flux-based critical levels are applicable for assessing the impacts of ozone on food security via affects on food availability and stability of food supplies. Flux-based response functions for effects of ozone on wheat (grain yield, protein yield and grain mass), potato (tuber yield), tomato (fruit yield), oilseed rape (oil content, seed yield), broccoli (floret yield), lettuce (biomass) and bean (pod yield) were reviewed. Approved for the derivation of critical levels were the functions

Supporting evidence, sources of uncertainty and further research

For each receptor, confidence is gained from the coherent pattern in response when combining experiments from different countries with different climatic conditions, and for crops for a range of varieties (Table 1). These functions had a similar level of significance to those using AOT40 as the ozone parameter (LRTAP Convention, 2010, Pleijel et al., 2007, Karlsson et al., 2007). However, the more biologically meaningful flux-based method provided a better fit to mapped data than AOT40,

Conclusion

In this paper we have provided an overview of the new/revised flux-based critical levels that have been agreed for use in assessment of risk of damage to crops, forest trees and (semi-)natural vegetation within the LRTAP Convention region. These critical levels and associated functions can be used to quantify impacts on food security, ecosystem services provided by forest trees, and the vitality of grasslands by following the guidance provided in LRTAP Convention (2010). Despite the

Acknowledgements

Gina Mills, Harry Harmens and Felicity Hayes wish to thank Defra (contracts AQ0810, AQ0816 and AQ0601), the LRTAP Convention and NERC for continued financial support of the coordination of the ICP Vegetation, and all the participants of the ozone group of the ICP Vegetation for their contributions to the review of the critical levels. Lisa Emberson and Patrick Büker would like to thank Defra for funding their research (contract AQ0601). The work by Håkan Pleijel, Per-Erik Karlsson and Helena

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