Growth and physiology of Hopea odorata planted within gaps in an acacia plantation acting as a nurse crop

Background: Mixtures of tropical acacia nurse crops and understorey native species have been established to aid forest restoration in Vietnam, but with partial success. Knowledge of physiological mechanisms underlying competitive interactions remains limited.Aims: To examine growth and physiological responses of Hopea odorata, a shade-tolerant dipterocarp, established within an Acacia hybrid (Acacia mangium × Acacia auriculiformis) nurse-crop plantation.Methods: H. odorata seedlings were planted within three 22-m diameter gaps in a 3-year-old Acacia hybrid plantation in Central Vietnam. Growth and physiology responses to an environmental gradient in gaps were examined over 2 years.Results: Growth rate and maximum rates of photosynthesis and stomatal conductance of H. odorata saplings increased significantly with increases in relative daily incident photosynthetically active radiation from 24% at the gap perimeter (GP) to 61% at the gap centre. Leaf N, P, and chlorophyll concentration were unaffected by po...