Diurnal pattern of acetaldehyde emission by flooded poplar trees

The emission of the tropospheric trace gas acetaldehyde was determined in l eaves of 4-month-old poplar trees (Populus tremula x P. alba) grown under c ontrolled environmental conditions in a greenhouse. Using a dynamic cuvette system together with a high sensitivity laser-based photoacoustic detectio n unit, rates of acetaldehyde emission were measured with the high time res olution of about 15 min. Submergence of the roots resulted in the emission of acetaldehyde by the leaves. The emission increased linearly before reach ing more or less steady-state values (ca 350 nmol m (- 2) min (- 1); ca 470 ng g (- 1) dry weight min (- 1)) after approximately 6 h. Prolonged floodi ng of poplar trees resulted in a clear diurnal rhythm of acetaldehyde emiss ion, The emission rates decreased when the light was switched off in the ev ening and peaked in the morning after the light was turned on again. This p attern significantly correlated with diurnal rhythms of stomatal conductanc e, photosynthesis, transpiration and with the concentrations of ethanol, th e assumed precursor of acetaldehyde, in the xylem sap of flooded poplar tre es. It may be concluded that under conditions of diminished stomatal conduc tance, acetaldehyde emission declines because its diffusive flux is reduced . Alternatively, reduced transpiration may decrease ethanol transport from the roots to the shoots and appreciable amounts of the acetaldehyde precurs or ethanol are lacking in the leaves. The present results support the view that acetaldehyde emitted by the leaves of plants is derived from ethanol p roduced by alcoholic fermentation in submerged roots and transported to the leaves with the transpiration stream.