Abstract
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.
Highlights
Non-pioneer or shade tolerant species develop morphological, anatomical and physiological adjustments under deep shade that are characterised by a higher investment in leaf area
Based on reports that variables related to photosynthesis 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
Growth increased up to 1400 lmol m-2 s-1 photo synthetically active radiation (PAR) and decreased at 2000 lmol m-2 s-1 PAR. This was related to the rate of photosynthesis (A) which showed the same tendency as photosystem II performance index (PIABS)
Summary
Non-pioneer or shade tolerant species develop morphological, anatomical and physiological adjustments under deep shade (shade tolerance syndrome) that are characterised by a higher investment in leaf area This is reflected in an increased leaf area ratio (LAR) and specific leaf area (SLA), and a decreased blade thickness because of the reduced elongation of mesophyll cells (Lambers et al 2008). These adjustments improve the capture of low light in highly shaded environments, where certain tropical tree species tend to have lower relative growth rates (RGR) (Souza and Valio 2003), higher chlorophyll concentrations (Goncalves et al 2005), higher photosynthetic activity (Silvestrini et al 2007), and lower concentrations of soluble carbohydrates (Marenco et al 2001; Mengarda et al 2012). The capacity of C. echinata to tolerate high irradiance was associated with increased soluble carbohydrate concentrations, increased length of mesophyll cells, higher water contents, and improved recovery of the photochemical capacity of plants transferred to full sunlight (Mengarda et al 2012)
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