Comparative effects of exogenous glycine betaine, kaolin clay particles and Ambiol on photosynthesis, leaf sclerophylly indexes and heat load of olive cv. Chondrolia Chalkidikis under drought

The aim of the present study was to investigate the effects of exogenous application of kaolin clay particles, glycine betaine and Ambiol on olive (Olea europaea L.) plants subjected to drought stress. Two years old self-rooted cv. Chondrolia Chalkidikis olive trees were subjected to two irrigation regimes, i.e. the fully irrigated and the water stressed trees, while they were treated with the three pre-mentioned products. Drought decreased the relative water content, the actual water content and the succulence of leaves significantly, while leaf tissue density was increased. Carbon assimilation rate, stomatal conductance and intrinsic water use efficiency were significantly reduced under drought stress conditions, while intercellular CO2 increased. Among the alleviating products tested, kaolin clay particles had a significant positive effect on leaf water content, succulence, leaf tissue density and leaf temperature under both drought and well irrigated conditions. Glycine betaine and kaolin clay particles when applied to drought stressed trees, resulted in increased CO2 assimilation rates compared to control. Furthermore, kaolin clay particles treated leaves exhibited high diurnal CO2 assimilation rates under drought conditions. Based on the results of the present study, kaolin clay particles and glycine betaine proved to be the most effective, among the applied products, on alleviating the negative effects of drought stress.

► Glycine betaine and kaolin clay particles ameliorate drought stress consequences.
► Stomatal as well as non-stomatal limitations on photosynthesis occur under drought.
► Kaolin efficacy depends on environmental conditions and morphological characteristics of the cultivar.
► Olive leaves experience high heat load during the course of a summer day.