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Variation in isorpene emission from Quercus rubra: sources, causes and consequences for estimating fluxes.
Funk, Jennifer*,1, Jones, Clive2, Lerdau, Manuel 1, Gray, Dennis1, Throop, Heather3, Hyatt, Laura4, 1 State University of New York, Stony Brook, NY2 Institute of Ecosystem Studies, Millbrook, NY3 Beloit College, Beloit, WI4 Rider University, Lawrenceville, NJ
ABSTRACT- Because studies examining the patterns and regulation of isoprene emission from plants usually monitor only a few individuals and/or causal factors, it is not known at what scale plants show the greatest variability in basal emission rate (BER) of isoprene. We measured BER from a total of 40 red oak (Quercus rubra) individuals from 2 field populations from 1997 to 1999. We found inter-plant variation to explain 60% of the total variance with only 40% being explained by leaf and branch combined. Absolute flux rates from the 2 populations, which differed in plant age, were similar. To examine temporal variation in BER, 10 individuals were measured repeatedly during the 1998 and 1999 growing seasons. During 1998, inter-plant variation explained most of the variance. Drought conditions during July of 1999 caused a substantial decline in BER for all plants. Thus, seasonal effects explained most of the variance in the 1999 dataset. Absolute flux rates were similar between years, however individual plants did not maintain consistent average flux rates between years. The causal factors for the large inter-plant variation observed in this study are uncertain but may include differences in plant history, microclimate or genotype. Seasonal patterns of BER were best explained by temperature and PAR integrated over the previous 6 hours (r2 = 0.40). Overall, we found BER to be highly variable between plants and within the growing season. Consequences of this leaf-level variability for modeling fluxes across larger spatial and temporal scales will be discussed.
Key words: hydrocarbon emission, atmospheric chemistry