Morpho-physiological adjustments reveal Araucaria angustifolia [(Bert.) O. Kuntze] plasticity of saplings under shade regimes

Abstract

Abstract This study aimed to investigate the morpho-physiological adaptations of Araucaria angustifolia saplings under different shade conditions. Saplings were grown for 21 months under full sunlight (S0%) and three shade levels: 30%, 50%, and 80% (S-30%, S-50% and S-80%, respectively). Growth, light-harvesting pigments (chlorophyll and carotenoids), chlorophyll fluorescence, and anatomical leaf structure were analyzed. Plants in S-0% and S-30% showed higher stem diameter, total and root dry mass, Dickson quality index, chlorophyll a/chlorophyll b ratio, carotenoids content, and electron transport rate. Conversely, shaded plants (S-50% e S-80%) exhibited physiological adaptations, compensating for the decreased light supply by primarily increasing the amount of chlorophyll and the quantum efficiency of photosystem II and reducing the thickness of their leaves. These results indicate that, despite the physiological plasticity to shade in Araucaria, the saplings grow better under a high-irradiance environment or low-shade condition (S-30%). In this sense, shaded cultivation of this species should be avoided in nurseries and reforestations due to the significant total dry mass reduction. This study highlights the importance of optimal light intensity to promote the growth of this endangered species.

Keywords

• Brazilian pine
• dry biomass
• leaf structure
• photosynthetic pigments
• reforestation