Research M Watch Autumn leaves release VOCs Autumn frosts in deciduous forests trigger significant releases of volatile organic compounds (VOCs) from leaves and may contribute to ground-
level ozone, according to new findings from the Austrian Alps. The concentration of natural VOCs after a hard frost was 2-1/2 to 10 times more than the concentration of VOCs from burning fossil fuels over one week in midNovember 1999. After the first hard frost in November 1999, scientists recorded daily peaks of plant VOCs and found that they correlated with warm daytime and freezing nighttime temperatures. The same pattern of VOC release was observed in the lab when scientists froze and thawed leaves of clover, grass, fir, and larch from the forests and fields surrounding Sonnblick. The researchers propose that frost destroys plant cells, which release wound compounds, such as hexanals, pentenol, and methylbutanals, in large amounts when they thaw (Geophys. Res. Lett. 2001, 28 (3), 507–510).
Modeling biodiversity Given fears that biodiversity may be declining precipitously worldwide, ecologists have been scrambling to determine how numbers of various species are changing. One of ecology’s more fundamental measures of biodiversity is the mathematical relationship connecting “species richness” and the test area in which a particular species has been laboriously counted. However, M. Crawley and J. Harral of Imperial College in the United 146 A
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Kingdom find that the relationship is not as simple as has been believed. In this study, the British researchers studied the flora in Berkshire County in southeastern England. All vascular plants, including native and alien, were counted, except those clearly planted. Replicated and randomized plant data were collected in 11 different spatial scales, ranging from 0.01 to 108 m2. These zone data were fitted to the model, in which species richness S is given by S = cAz, where c is the concentration of species in an area A. The exponent z is typically believed to be ~0.25. However, the researchers found a greater variation in the exponent. At small scales (
