Photosynthesis, growth, and leaf nutrients of mahogany and jatoba seedlings acclimated to direct sunlight

Abstract

The objective of this work was to evaluate how the mahogany and jatoba species, with different growth rates, respond to full sunlight acclimatization during their juvenile stage. Three- and eight-month-old seedlings of mahogany and jatoba, respectively, were grown under low light and exposed to six independent full sunlight acclimation times for 30 days: 0.0 hour (control), 1.5 hour (11h15–12h45), 3.0 hours (10h30–13h30), 6.0 hours (9h00–15h00), 9.0 hours (7h30–16h30), and 12.0 hours (6h00–18h00). Then the plants were transferred to outdoor conditions the whole day for 120 days. Leaf gas exchange, leaf traits, plant growth, biomass allocation, and leaf nutrient contents were evaluated. In both species, photosynthetic rates increase with the length of full sunlight exposure, associated with an increase in stomatal conductance. The variable fluorescence/maximal fluorescence ratio decreases after exposure to acclimation times of 6.0, 9.0 and 12 hours, particularly in mahogany. Mahogany presents greater growth rates and leaf production than jatoba when exposed to full sunlight. Macronutrient concentrations, except of nitrogen and phosphorus, are higher in jatoba than in mahogany. Mahogany, a fast-growing species, acclimates to full sunlight primarily through the production of new leaves, while jatoba, a slow-growing species, acclimates to full sunlight based on its leaf traits, especially on its low specific leaf area (high leaf thickness).