Keeley and Fotheringham (1997) report that oxides of nitrogen (NOx) can
trigger seeds to germinate in Mediterranean climates like those of
California. Many plant species in these climate zones are stimulated to
germinate by the occurrence of forest fires, which clear underbrush and
give new seedlings a chance for survival. But common air pollutants
emitted from high temperature burning from power plants, factories, and
automobiles may have the same effect on such seeds. This would cause
premature germination of seeds at time when underbrush has not been cleared
and emergent seedlings have little chance for survival.
Reference
Keeley, Jon E. and C. J. Fotheringham, 1997: Trace Gas
Emissions and Smoke-Induced Seed Germination. Science, 276, 1248-1250.