Fluctuations in Leaf Carbon Assimilation as Affected by Root-zone Temperature and Growth Environment

Abstract

Short-term effects of root-zone temperatures (RZT) of 28, 33, 38, and 43C for 6 hours daily on container-grown Musa spp. (AAA) `Grande Naine' and Ixora chinensis L. `Maui' were determined under greenhouse and growth room conditions. Diurnal fluctuation of leaf carbon assimilation (LCA) was altered by treatments. In the growth room at 43C, the maximum LCA occurred about midday for banana, but not until afternoon in ixora. LCA was highest (0.53 mg CO2/m2 per sec) in banana with a 33C RZT under greenhouse conditions, while it was equally high (0.74 mg CO2/m2 per sec) at 33 and 38C in a growth room. In ixora, 33C induced the highest LCA (0.40 mg CO2/m2 per sec) in the greenhouse at 1200 hr, but there were no apparent differences in midday LCA between plants with RZT of 28, 33, and 38C in the growth room. Effects of RZT and environment on the daily fluctuations of gaseous exchange processes raise questions about using measurements at only one time during the day to separate treatment effects.