How does Cariniana estrellensis respond to different irradiance levels?
2019
Portela, Flávia Carolina Santos | Macieira, Bernardo Pretti Becacici | Zanetti, Leonardo Valandro | Gama, Vinícius Novo | Silva, Diolina Moura | Milanez, Camilla Rozindo Dias | Cuzzuol, Geraldo Rogério Faustini
Based on reports that variables related to photosynthesis (net assimilatory ratio and chloroplast pigments) are more plastic than the morphological and biochemical variables in a climax tropical species, Cariniana estrellensis, under contrasting irradiance, we hypothesised that plasticity of gas exchange variables is higher in relation to growth, biochemical and anatomical variables. Plants that were 14 months old were subjected to 200 up to 2000 µmol m⁻² s⁻¹ of photo synthetically active radiation (PAR) for 140 days. Growth increased up to 1400 µmol m⁻² s⁻¹ PAR and then decreased at 2000 µmol m⁻² s⁻¹ PAR (full sunlight). This was related to the rate of photosynthesis (A) which showed the same tendency as photosystem II performance index (PIABS). The greater thickness of the secondary xylem at 1400 µmol m⁻² s⁻¹ PAR indicated a higher water conductance capacity. The decrease in specific leaf area, elongation of mesophyll cells, and increase in stomatal density observed at higher irradiances were associated with higher leaf fructose and sucrose concentrations. We concluded that the better growth in partial shade was due to higher photosynthetic capacity. On the other hand, photosynthesis was inhibited equally in full sun and deep shade. The high adjustment capacity of C. estrellensis to wide amplitudes of irradiance was provided by greater plasticity of gas exchange variables in relation to growth, anatomical, and biochemical variables.
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