Responses to ozone pollution of alfalfa grown with increasing levels of salt stress

It’s well known that ozone is the most dangerous atmospheric pollutant for vegetation and reduces yield of several crops (Ferretti et al., 2007). Considering that ozone enters into plant tissues through the stomata, all the factors that reduce stomatal conductance also reduce ozone injuries to crops (Fagnano and Merola, 2007). Among these factors, in Mediterranean area increasing problems of watertable and soil salification are widespread reported. Salt stress reduced ozone sensitivity of some crop (Maggio et al., 2007), thanks to its effect on stomatal conductance and antioxidants production. The aim of this paper was to verify if irrigation with saline water can modify alfalfa responses to ozone pollution. From this experiment, it was confirmed that environmental conditions can strongly modify the response of plants to ozone pollution. Therefore, the thresholds for the protection of vegetation actually based on plant exposure to ozone tropospheric concentration are not suitable for the Mediterranean cropping systems, because these environments are characterized by multiple stresses (i.e. drought, salinity and ozone) that can modify the response of plants to the single stresses. For these reasons a ozone flux approach that takes into account other pedoclimatic stressors, therefore based on the real ozone dose absorbed by plants, will be more suitable for estimating ozone damages to crops in the different agro-environmental conditions of Europe.