RESUMEN
Ozone (O3) pollution poses a significant threat to global crop productivity, particularly for wheat, one of the most important staple foods. While bread wheat (Triticum aestivum) is unequivocally considered highly sensitive to O3, durum wheat (Triticum durum) was often found to be more tolerant. This study investigated the O3 dose-response relationships for durum wheat in the Mediterranean region, focusing mainly on grain yield losses, and utilizing the phytotoxic ozone dose (POD) metric to describe the intensity of the stressor. The results from two experiments with Open-Top Chambers performed in 2013 and 2014 on two relatively sensitive durum wheat cultivars confirmed that this wheat species is far more tolerant than bread wheat. The use of a local parameterization of a stomatal conductance model based on field measurements did not significantly improve the dose-response relationships obtained in comparison to the generic parameterization suggested by the Mapping Manual of the United Nations Economic Commission for Europe (UNECE). The POD6 critical level of 5 mmolO3 m-2 for 5% grain yield loss was remarkably higher than the one established for bread wheat with analogous experiments, highlighting that O3 risk assessments based on bread wheat may largely overestimate the damage in the Mediterranean region where durum wheat cultivation prevails.
RESUMEN
Tropospheric ozone (O3) is a secondary atmospheric pollutant known to cause negative effects on vegetation in terms of physiological oxidative stress, growth rate reductions and yield losses. In recent years, dose-response relationships based on the O3 stomatal flux and effects on the biomass growth have been defined for several crop species. This study was aimed at developing a dual-sink big-leaf model for winter wheat (Triticum aestivum L.) to map the seasonal Phytotoxic Ozone Dose above a threshold of 6nmolm-2s-1 (POD6) in a domain centered on the Lombardy region (Italy). The model runs on local measured data of air temperature, relative humidity, precipitation, wind speed, global radiation and background O3 concentration provided by regional monitoring networks, and includes parameterizations for the crop's geometry and phenology, the light penetration within the canopy, the stomatal conductance, the atmospheric turbulence, and the soil water availability for the plants. For the 2017 an average POD6 of 2.03mmolm-2PLA (Projected Leaf Area) was found for the Lombardy regional domain, corresponding to an average relative yield loss of 7.5%, using the finest spatio-temporal resolution (1×1km2 and 1-h). An analysis of the model's response to different spatio-temporal resolutions (from 2×2 to 50×50km2 and from 1 to 6 h) suggests that coarser resolution maps underestimated the average POD6 regional value from 8to16%, and were unable to detect O3 hotspots. Nevertheless, resolutions of 5×5km2 1-h, and 1×1km2 3-h, can still be considered reliable for the estimation of the O3 risk at the regional level since they presented relatively low root mean squared error. Furthermore, although temperature was the main limiting factor for the wheat stomatal conductance in most of the domain, soil water availability emerged as the key factor for determining the spatial patterns of the POD6.