Physiological Performance of Pyrus pyraster L. (Burgsd.) and Sorbus torminalis (L.) Crantz Seedlings under Drought Treatment

In this study, seedlings of Pyrus pyraster and Sorbus torminalis were grown for 60 days in the regulated environment of a growth chamber under different water regimes. The measured indicators were the growth and distribution of mass to organs, total biomass, root to shoot mass ratio (R:S), and gas exchange parameters (g(s), E, A(n), and water use efficiency (WUE)). The amount of total biomass was negatively affected by drought. Differences between species were confirmed only for the dry matter of the leaves. P. pyraster maintained the ratio of the mass distribution between belowground and aboveground organs in both variants of the water regime. S. torminalis created more root length for a given dry-mass under drought treatment, but its R:S was lower compared to P. pyraster. The water potential of the leaves (Ψ(wl)) was affected by substrate saturation and interspecific differences. P. pyraster had a demonstrably higher water potential and maintained this difference even after prolonged exposure to drought. After 30 days of different water regimes, Pyrus maintained higher values of g(s), A(n), and E in control and drought treatments, but over a longer period of drought (after 50 days), the differences between species were equalized. The changes of the leaf gas exchange for Pyrus were accompanied by a significant increase in WUE, which was most pronounced on the 40th day of the experiment. A significant and strong relationship between WUE and g(s) was demonstrated. The results confirmed the different physiological performances of seedlings of tree species and the different mechanisms of their response to water scarcity during drought treatment. P. pyraster presented more acclimation traits, which allowed this taxon to exhibit better performance over a longer period of water scarcity.