PHOTOSYNTHETICA 48 (3): 421-429, 2010 421 Diurnal and seasonal variation in photosynthesis of peach palms grown under subtropical conditions M.L.S. TUCCI *,+ , N.M. ERISMANN ** , E.C. MACHADO ** , and R.V. RIBEIRO ** Section of Tropical Plants, Center for Research and Development in Horticulture, Instituto Agronomico, P.O. Box 28, 13012-970, Campinas/SP, Brazil * Section of Plant Physiology, Center for Research and Development in Ecophysiology and Biophysics, Instituto Agronomico, P.O. Box 28, 13012-970, Campinas/SP, Brazil ** Abstract 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 CO 2 assimilation (P N ), observed in mid summer, reached about 15 ȝmol 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 P N 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 (g s ) followed the same pattern of P N , 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 (F v /F m ) 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 (VPD leaf-air ) and P N and a positive correlation between P N and g s 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 (T air ) and VPD leaf-air impose more significant effects over P N 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. Additional key words: Bactris gasipaes; chlorophyll fluorescence; gas exchange; stomatal conductance; vapour pressure deficit. Introduction Growing the Amazonian peach palm (Bactris gasipaes Kunth) for heart-of-palm production has been an important alternative to decrease the predatory exploita- tion of the native palm Euterpe edulis Mart. from the Atlantic forest, which in recent decades has been included among the species threatened by extinction. The area used for cultivating peach palm in São Paulo State, Brazil, corresponds to approximately 3,900 ha (Anefalos et al. 2007), and is expanding. In their natural habitats peach palms are under tropical ——— Received 15 March 2010, accepted 2 July 2010. + Corresponding author; fax: +55-1932877530, e-mail: tucci@iac.sp.gov.br Abbreviations: AGR – absolute growth rate; C i – intercellular CO 2 concentration; ETR – apparent electron transport rate; F – instantaneous fluorescence of light-adapted state; F 0 – minimal fluorescence yield of dark-adapted state; F m – maximal fluorescence of dark-adapted state; F m ’ – maximal fluorescence of light-adapted state; F v – variable fluorescence of dark-adapted state; F v /F m – maximal PSII quantum yield; g s – stomatal conductance; P N – net CO 2 assimilation; PPFD – photosynthetic photon flux density; PSII – photosystem II; T air – air temperature; T leaf – leaf temperature; VPD air – air vapour pressure deficit; VPD leaf-air – leaf-to- air vapour pressure difference; ΔF – variable fluorescence of light-adapted state; ΔF/F m ’ – effective PSII quantum yield; Ψ leaf – leaf water potential. Acknowledgments: The authors gratefully acknowledge the Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp, Brazil) for financial support (n° 00/02782-6). E.C. Machado and R.V. Ribeiro are also grateful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil) for the fellowship granted.