Irrigation-driven modulation of growth and stress resilience in cork oak (Quercus suber L.) seedlings in nursery environments

Abstract

Cork oak (Quercus suber L.) is a keystone species of Mediterranean forestry, increasingly threatened by prolonged droughts and anthropogenic pressures. Improving nursery seedling quality is therefore essential for successful reforestation. This study evaluates the effects of three irrigation regimes (i) daily manual watering (IN), (ii) irrigation triggered when soil moisture falls below 30% (IB), and (iii) irrigation at field capacity based on daily container weight loss (IC), and two container types (rigid pots: 2000 cm³; alveolate trays: 500 cm³ per cell) on the morphological development of Q. suber seedlings over six months. A total of 210 acorns from the Maâmora forest were sown in a fully crossed two-factor design. A two-way ANOVA revealed significant main effects of irrigation regime (F = 18.43, p < 0.001) and container type (F = 12.67, p < 0.001), as well as a significant interaction (F = 4.21, p = 0.019) on shoot height. The IC treatment consistently produced the best results: shoot height 24.64 ± 0.8 cm, root length 63.33 ± 2.1 cm, and leaf dimensions 4.88 × 3.33 cm. The IB group displayed stress signs, including reduced leaf area and lower biomass. Rigid pots promoted shoot elongation but induced root deformation (chignon) in 82% of seedlings, compared to only 14% in alveolate trays. These findings demonstrate that combining field capacity irrigation with alveolate container systems significantly enhances seedling resilience and quality for Mediterranean reforestation programs.