The photosynthetic dynamics of the tropical pioneer species, Byrsonima sericea DC., were studied during the regeneration process of
a native forest by evaluating ecophysiological (gas exchange, chlorophyll a fluorescence and photosynthetic pigment contents) and
anatomical parameters of plants in sunny and shady environments. Ecophysiological evaluations were carried out monthly for one
year, encompassing both a dry and a rainy season. Byrsonima sericea DC. presents anatomical plasticity that enables it to establish in
environments with contrasting light regimes. In sunny conditions, it produced a thicker leaf (about 420 mm) and flat adaxial epidermis,
whilst in the shade, leaves had a thinner convex adaxial epidermis (about 395 mm). No differences were found in the compositions of
the pigments in the different environments, however, during the dry season, the plants presented a significantly higher concentration of
photosynthetic pigments. In the sun, plants showed decreases in Fv/F0 ratio (in the rainy season) and NPQ (in the dry season), but no
difference was observed between plants that were in the sun or in the shade. A significantly higher net photosynthetic rate was found
only in the rainy season in the plants in the sun, compared to shaded plants (9.9±0.8 and 7.4±0.3 μmol m-2s-1, respectively). Significant
increase in transpiration was observed in plants in the shade during the dry season, but no alterations were observed in the water use
efficiency. Ecophysiological data suggest that mainly plants overexposed to the sun underwent water limitations during the dry season
and that, in the rainy season, these plants increased their net photosynthetic rate, possibly due to the greater drainage force resulting
from increased growth during this period. Data suggest that anatomic alterations, namely the convex adaxial epidermis, could aid in the
supply of light to shaded plants during both seasons, precluding changes in the pigments, such as the increase in chlorophyll b usually
observed in shaded plants, but not detected in the present study. Another consequence of the greater quantity of light captured by these
shade plants is that during the dry season their net photosynthetic rate was not different from that of plants in a sunny environment.
However, when water was not a limiting factor, a better photosynthetic performance was observed in this pioneer specie in open spaces.
