Comparative effects of water deficit and enhanced UV-B radiation on photosynthetic capacity and leaf anatomy traits of two grapevine (Vitis vinifera L.) cultivars

The effects of drought and enhanced UV-B radiation on photosynthetic and leaf anatomical characteristics were studied in two different grapevine genotypes (Vitis vinifera L. cvs 'Romeiko' and 'Soultanina'), which were grown outdoors in 25 L pots containing a peat:perlite:sand (3:1:1, v/v/v) potting mix. The plants were subjected to three levels of UV-B radiation (i) ambient, (ii) intermediate (ambient plus 15 % UV-B radiation), (iii) high (ambient plus 30 % UV-B radiation) and two irrigation regimes (i) well-watered (irrigated on daily basis to substrate capacity) and (ii) drought-stressed (irrigated daily with the 50 % of the amount of water provided to well-watered plants). Both abiotic stressors induced a significant decrease in net photosynthesis (Pn) while the combination of drought and elevated UV-B radiation appeared to have synergistic effects on photosynthetic rate. At leaf anatomical level, drought resulted in the development of idioblastic cells in leaves of both grapevine varieties as well as in the reduction of leaf expansion rate, total lamina thickness and total biomass per leaf area whereas leaf tissue density considerably increased. On the other hand, enhanced UV-B radiation did not affect leaf anatomical characteristics of both genotypes in a similar way. In particular, different responses, closely depended to UV-B levels applied, were observed concerning the chlorenchymatic tissue and total lamina thickness. Moreover, the stimulation of UV-B absorbing compounds biosynthesis under enhanced UV-B radiation, could not manage to preserve photosynthetic performance. The implication of the watering regime and the UV-B in the induction of leaf anatomical and morphological alterations in net photosynthesis is discussed.