Comparison of Morphological and Physiological Traits between Pinus brutia, Pinus halepensis, and Their Vigorous F1 Hybrids

Hybrids between Pinus brutia Ten. and Pinus halepensis Mill. have mainly been investigated with respect to their growth rate. Less attention has been paid to factors that contribute to their resistance to drought, although the hybrids have been shown to thrive over P. brutia in semi-arid regions. To understand the superior hybrid phenotype, we investigated morphological traits, growth parameters, and physiological response to drought stress in P. brutia, P. halepensis, and their vigorous hybrids. Rooted cuttings were propagated from mature trees and were examined in a high-throughput gravimetric system to evaluate their response to drought. Higher root-to-shoot ratio, needle length, and leaf mass per area (LMA) were observed in the hybrids compared to the two parental species. P. halepensis demonstrated higher transpiration rates (E) and stomatal conductance (g_sc) than P. brutia, and an earlier reduction in E and g_sc in response to drought stress. Similar to P. brutia, the hybrids showed low E and g_sc, and an early stomatal closure in response to drought similar to P. halepensis. Our study suggests that the hybrids exhibit a unique combination of traits that may contribute to forest resilience in semi-arid regions undergoing climate change.