Assessing the role of soil water limitation in determining the Phytotoxic Ozone Dose (PODY) thresholds

TitoloAssessing the role of soil water limitation in determining the Phytotoxic Ozone Dose (PODY) thresholds
Tipo di pubblicazioneArticolo su Rivista peer-reviewed
Anno di Pubblicazione2016
AutoriDe Marco, Alessandra, Sicard P., Fares S., Tuovinen J.-P., Anav A., and Paoletti E.
RivistaAtmospheric Environment
Parole chiaveAbies alba, Fagus sylvatica, forestry, Mediterranean forest, Ozone, Ozone risk assessment, Phytotoxic ozone dose, Pinus cembra, Quercus ilex, Risk assessment, Risk perception, Soil moisture, Soil water content, Soils, Threshold

Phytotoxic Ozone Dose (PODY), defined as the accumulated stomatal ozone flux over a threshold of Y, is considered an optimal metric to evaluate O3 effects on vegetation. PODY is often computed through the DO3SE model, which includes species-specific parameterizations for the environmental response of stomatal conductance. However, the effect of soil water content (SWC) on stomatal aperture is difficult to model on a regional scale and thus often ignored. In this study, we used environmental input data obtained from the WRF-CHIMERE model for 14,546 grid-based forest sites in Southern Europe. SWC was obtained for the upper 10 cm of soil, which resulted in a worst-case risk scenario. PODY was calculated either with or without water limitation for different Y thresholds. Exclusion of the SWC effect on stomatal fluxes caused a serious overestimation of PODY. The difference increased with increasing Y (78%, 128%, 237% and 565% with Y = 0, 1, 2 and 3 nmol O3 m−2 s−1, respectively). This behaviour was confirmed by applying the same approach to field data measured in a Mediterranean Quercus ilex forest. WRF-CHIMERE overestimated SWC at this field site, so under real-world conditions the SWC effect may be larger than modelled. The differences were lower for temperate species (Pinus cembra 50–340%, P. sylvestris 57–363%, Abies alba 57–371%) than for Mediterranean species (P. pinaster 87–356%, P. halepensis 96–429%, P. pinea 107–532%, Q. suber 104–1602%), although a high difference was recorded also for the temperate species Fagus sylvatica with POD3 (524%). We conclude that SWC should be considered in PODY simulations and a low Y threshold should be used for robustness. © 2016 Elsevier Ltd


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