Shade role in facilitation drought stress symptoms on physiology of mount Atlas mastic (Pistacia atlantica Desf.) seedlings

This investigation was carried out in Albroz research station complex (Karaj, Iran) during 2014 summer. Mount Atlas mustic (Pistacia atlantica Desf.) seedlings were treated by drought (moderate, sever and without drought stress) and shading (low, moderate and without shade) factors in a split plot experiment based on a randomized complete block design. After one month, physiological characteristics of leaves including RWC, soluble sugars, proline and pigments content, catalase enzyme activity and ion leakage were studied. Drought stress caused severe decrease in RWC and a, b and total chlorophyll contents. In contrast, shade by ameliorating drought stress significantly increased these parameters. Drought induced tolerance mechanisms in saplings and increased proline and carotenoid content while shade decreased these parameters significantly as well as a to b chlorophyll ratio. Interaction of drought and shade was significant for a chlorophyll and catalase activity, suggested that, drought treatments showed different responses to shade. Overall, results revealed positive effect of shade on drought induced saplings.