GAS-EXCHANGE RESPONSE OF GRAPEVINE LEAVES UNDER FLUCTUATING LIGHT

Gas exchange responses to lightflecks of different frequency and durat ion were studied in mature grapevine leaves. Light-response curves und er intermittent light showed lower carbon exchange rate (CER) than con tinuous light at non-saturating PFD levels (10-500 mu mol m-2s-1). Whi te-dark and white-green alternating light of equal bright and shade pe riods at 0.33-5.33 Hz systematically resulted in improved light utiliz ation as compared to high continuous light. Transpiration (T) was slig htly more limited than the CER under intermittent light, resulting in higher water use efficiency. No differences in carboxylation efficienc y were found by comparing the high continuous light treatment to white -dark lightflecks at 0.33 and 2.67 Hz. Our results show that, under sh ort-term alternating light, CER of the grapevine leaf fully responds t o the mean PFD level resulting from light oscillations.