Combined salinity and ambient ozone stress effects on olive physiology and biochemistry

Abstract

The presence of high ambient ozone concentrations is common in the Mediterranean region, while saline water is often used for olive irrigation. The effects of this combined stress on physiology and biochemistry were studied in young olive trees. Two-year-old ‘Konservolea’ and ‘Kalamata’ olive plants (Olea europaea L.) grafted on seedling rootstock were grown in sand:perlite mixture irrigated with half strength Hoagland’s solution containing or not 100 mM NaCl. In open top chambers, the plants received outside air with ambient ozone or charcoal-filtered air from April to October in 2006 and 2008. Specific leaf mass, chlorophyll content, net photosynthetic and transpiration rate, stomatal conductance, chlorophyll fluorescence, midday stem water potential and superoxide dismutase, catalase and ascorbate peroxidase activities were measured periodically from June to September. On October 15, 2006 and 2008, the plants (after sampling fresh tissues for soluble sugar and starch analysis) were divided into roots, trunk, old shoots, new shoots, old leaves and new leaves. Shoot length and total leaf area were initially measured and dry mass at each plant part was measured after complete dryness. Both studied olive cultivars showed similar behavior to salinity stress possibly due to the seedling rootstock on which both cultivars were grafted. Irrigation with 100 mM NaCl solution negatively affected most of the leaf physiological parameters evaluated resulting in reduced productivity. This was clearly evaluated by the dry mass partitioning data, where total tree dry matter decreased due to salinity as shoot length, leaf surface area and dry matter accumulated to new leaves, new shoots and roots was significantly reduced. Salinity also increased neutral sugar concentration in new shoots and leaves and decreased neutral sugarconcentration in roots. The opposite was often found for starch concentration. Ambient ozone concentrations from May to September able to damage plants (daylight mean ozone concentration >60 nL L-1) did not affect the olive leaf functions studied, dry matter accumulation and partitioning and stored sugar metabolism to any of the plant parts of young olive trees. This clearly shows that young olive trees are relatively resistant to ozone levels found around the Mediterranean region. The combination of salinity and ambient ozone stress did not result in any further effectsto leaf physiological parameters besides the ones from the salinity stress alone.