Document: JEN-3-34-26
Diurnal patterns of isoprene emission and the potential role of substrate regulation.
FUNK, J.L.* 1, H.M.FULLER 2, C.BAKER 2, C.G.JONES 2 and M.T.LERDAU 1
State University of New York, Stony Brook, NY 11794-5245 USA 1
Institute of Ecosystem Studies, Millbrook, NY 12545 USA 2
Abstract:
Isoprene emission from plants is one of the principal ways in which plant processes alter atmospheric chemistry. Diurnal variations in isoprene emission from plants under ambient conditions are often attributed to daily patterns of light intensity and leaf temperature. However, diurnal variations in emission that are independent of light and temperature also occur but have not been examined in as much detail. These light- and temperature-independent diel variations may provide biological insight into the regulation of isoprene emission. We measured diurnal patterns of photosynthesis and isoprene emission at constant light and temperature from nursery and field grown eastern cottonwood (Populus deltoides) and red oak (Quercus rubra) individuals using gas exchange techniques and gas chromatography. Significant increases in isoprene emission were observed throughout the day in all nursery and field cottonwood, with daily increase rates ranging from 20 to 160%. In contrast, diurnal trends were absent or very small in oaks. Differences in diurnal patterns of carbon accumulation and export between P. deltoides and Q. rubra could have accounted for contrasting diurnal emission patterns, suggesting that substrate availability may influence emission capacity. To explore the potential mechanism of substrate regulation of isoprene emission, P. deltoides saplings were shaded for 24 hours to prevent carbon accumulation within the leaf resulting from photosynthesis. Shaded individuals displayed significant diurnal increases in emission, although rates were significantly lower than in non-shaded controls. The presence of diurnal emission patterns in the absence of photosynthate accumulation suggests that substrate alone does not determine emission capacity. We conclude that both substrate availability and enzymatic activity may regulate isoprene emission capacity.
Keywords: isoprene emission, diurnal variation, Populus deltoides
This abstract is being presented at: 8:30 AM in session:
Oral Session #1: Plant Carbon Allocation.