The Amazonian peach palm (Bactris gasipaes Kunth) has been grown for heart-of-palm production under subtropical conditions. As we did not see any substantial study on its photosynthesis under Amazonian or subtropical conditions, we carried out an investigation on the diurnal and seasonal variations in photosynthesis of peach palms until the first heart-of-palm harvest, considering their relationship with key environmental factors. Spineless peach palms were grown in 80-L plastic pots, under irrigation. Gas exchange and chlorophyll fluorescence emission measurements were taken in late winter, mid spring, mid summer and early autumn, from 7:00 to 18:00 h, with an additional chlorophyll fluorescence measurement at 6:00 h. The highest net CO2 assimilation (PN), observed in mid summer, reached about 15 μmol m-2 s-1, which was about 20% higher than the maximum values found in autumn and spring, and 60% higher than that in winter The same pattern of diurnal course for PN was observed in all seasons, showing higher values from 8:00 to 9:00 h and declining gradually from 11:00 h toward late afternoon. The diurnal course of stomatal conductance (gs) followed the same pattern of
PN, with the highest value of 0.6 mol m-2 s-1 being observed in February and the lowest one (0.23 mol m-2 s-1) in September. The maximal quantum yield of photosystem II (Fv/Fm) was above 0.75 in the early morning in all the months. The reversible decrease was observed around midday in September and October, suggesting the occurrence of dynamic photoinhibition. A significant negative correlation between the leaf-air vapour pressure difference (VPDleaf-air) and PN and a positive correlation between PN and gs were observed. The photosynthesis of peach palm was likely modulated mainly by the stomatal control that was quite sensible to atmospheric environmental conditions. Under subtropical conditions, air temperature (Tair) and VPDleaf-air impose more significant effects over PN of peach palm than an excessive photosynthetic photon flux density (PPFD). The occurrence of dynamic photoinhibition indicates that under irrigation, peach palms appeared to be acclimated to the full-sunlight conditions under which they have been grown. and M. L. S. Tucci ... [et al.].