Intraspecific Variation in Drought and Nitrogen-Stress Responses in Pedunculate Oak (Quercus robur L.) Half-Sib Progeny.

Pedunculate oak (Quercus robur L.) face increasing threats from drought and nutrient limitation under climate change, yet their genetic variation may have adaptive potential. We examined the responses of pedunculate oak (Quercus robur L.) half-sib progeny from five maternal trees (1, 12, 32, 57, and 60) to water stress (WS), nitrogen limitation (NL), and combined WS+NL. WS reduced leaf relative water content (RWC) by 18-32% in all families and decreased proline only in two families (233.57 and 209.1), while four families (63.12, 149.1, 303.32, and 339.57) showed 1.7-2.0-fold proline accumulation. Exposure to WS+NL inhibited height and diameter growth in family 339.57 and diameter growth in families 23.12, 303.32 and 405.60, relative to the control. NL decreased chlorophyll (Chl) in two families (23.12 and 405.60) 1.5-fold and increased carotenoids in one of them (405.60) and RWC by 29% and 12% in 23.12 and 303.32 families, respectively. ROS-scavenging activities of catalase (CAT), guaiacol-dependent peroxidase (POD), and superoxide dismutase (SOD) enzymes increased 1.4- to 26.7-fold across all families except 151.1. Overall, families 303.32 and 339.57 were the most resilient to WS, NL, and WS+NL, whereas 233.57 and 151.1 were the most sensitive to WS, 23.12 to NL, and 405.60 to both stresses. These results highlight the family-level variation in stress responses and provide a basis for selecting resilient oak genotypes for forestry and conservation.