Research papers

Ozone dynamics in a Mediterranean Holm oak forest: comparison among transition periods characterized by different amounts of precipitation


Tropospheric ozone (O3) is one of the most toxic compounds for plants in the atmosphere. The large amount of anthropogenic O3 precursors in the urban areas promote O3 formation, thus making Mediterranean forests located in periurban areas particularly vulnerable to this pollutant. O3 flux measurements have been carried out using the Eddy Covariance technique over a Holm oak forest located 25 Km from Rome downtown, inside the Presidential Estate of Castelporziano (Italy).Two transition periods - early Spring and late Fall - in two consecutive years were examined. The uncommon low precipitation recorded in both transition periods in 2012 allowed to evaluate the influence of water availability on O3 fluxes during seasons which are not commonly affected by drought stress.Overall, the forest canopy showed to be a net sink of O3, with peak values of mean daily O3 fluxes of -8.9 nmol m-2s-1 at the beginning of flowering season and -4.6 nmol  m-2s-1 at the end of Fall.

O3 fluxes were partitioned between stomatal and non stomatal sinks using the evaporative/resistive method based on canopy transpiration in analogy with an Ohm circuit. By comparison of the two years, water availability showed to be an important limiting factor during Spring, since in this season plants are more photosynthetically active and more sensitive to water availability, while in Fall, under conditions of low stomatal conductance,  the dependence on water availability was less appreciated.


ozone fluxes; O3; Holm oak; Mediterranean forest; Eddy Covariance; drought stress; pollution

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Altimir N., Kolari P., Tuovinen J.-P., Vesala T., Bäck J., Suni T., Kulmala M., Hari P.

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