PARENT SESSION
Poster Session #28: Gas Exchange.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Changes in photosynthesis during leaf expansion in Eucalyptus sieberi.

CHOINSKI, JOHN^*,1, EAMUS, DEREK², RALPH, PETER², ¹ UNIVERSITY OF CENTRAL ARKANSAS, CONWAY, AR² UNIVERSITY OF TECHNOLOGY, SYDNEY, NSW, AUSTRALIA

ABSTRACT- Growth, pigment levels and various photosynthesis parameters were measured in expanding leaves of Eucalyptus sieberi L.A.S. Johnson. E. sieberi trees were studied growing in sandstone plateau woodland communities in Royal National Park south of Sydney (New South Wales). Young leaves (horizontally oriented to maximize light exposure) were found to be conspicuously red until they reached approximately 75% of their full size. As the leaves expanded, anthocyanin content declined and chlorophyll levels proportionately increased. Young red leaves showed net negative carbon assimilation rates, although CO₂ assimilation rate, transpiration rate, stomatal conductance, actual quantum yield of PSII (_PSII) and apparent electron transport rate (ETR) all increased in a similar pattern as the leaves expanded. Measurements of maximum quantum yield of dark-adapted leaves (Fv/Fm) were also correlated with leaf area. Younger leaves had lower Fv/Fm ratios than did mature leaves, whether measured at midday or two hours after sunset, indicating that young leaves exhibited some degree of chronic photoinhibition. It is concluded that E. sieberi exhibits a transient red pattern of anthocyanin expression and that photosynthesis is limited in young leaves because of low stomatal conductance, low chlorophyll content, immature chloroplasts and an attenuation of light caused by anthocyanins.

KEY WORDS: Eucalyptus sieberi, photosynthesis, anthocyanin