Suitability of four main Mediterranean tree crops for their growth in peri-urban agriculture and restoration (Gabes, Tunisia).

In order to increase the knowledge about crop tolerance to air pollutants in the different agroclimatic zones of the world, so that they can be efficiently considered for improving peri-urban agriculture, increasing the success of restoration projects, or enhancing air quality in polluted sites, the suitability of four economical valuable tree crops of the Mediterranean agriculture were studied under field conditions: date palm tree (Phoenix dactylifera L.), pomegranate (Punica granatum L.), fig tree (Ficus carica L.), and olive tree (Olea europaea L.). The measurement of biochemical markers such as ascorbic acid content, leaf relative water content, leaf total chlorophyll and leaf extract pH, at two contrasted air quality sites, a polluted site located around Gabes (Tunisia) industrial area and a control site, allowed the assessment of the air pollution tolerance index (APTI) and anticipated performance index (API) for the assayed species. Results showed obvious differences between the evergreen and the caducifolious tree crops assayed. Phoenix dactylifera tree (API = 6) was classified as an excellent performer for growing under poor air quality, followed by Olea europaea tree (API = 2) which was classified as a moderate performer. Both of trees can be recommended for successful results in peri-urban agriculture and restoration projects of polluted areas in the Mediterranean climate; on the contrary, the suitability of the Punica granatum (API = 1) was very poor, but still potentially interesting as a biological indicator of air pollution. Regarding the Ficus carica tree (API = 0), this species is not suitable for growing in air-polluted areas.