Scientists from NASA's Goddard Space Flight Center in Greenbelt, Md., have produced groundbreaking global maps of land plant fluorescence, a difficult-to-detect reddish glow that leaves emit as a byproduct of photosynthesis. While researchers have previously mapped how ocean-dwelling phytoplankton fluoresce, the new maps are the first to focus on land vegetation and to cover the entire globe.
To date, most satellite-derived information related to the health of vegetation has come from "greenness" indicators based on reflected rather than fluorescent light. Greenness typically decreases in the wake of droughts, frosts, or other events that limit photosynthesis and cause green leaves to die and change color.
However, there is a lag between what happens on the ground and what satellites can detect. It can take days --- even weeks -- before changes in greenness are apparent to satellites.
Chlorophyll fluorescence offers a more direct window into the inner workings of the photosynthetic machinery of plants from space. "With chlorophyll fluorescence, we should be able to tell immediately if plants are under environmental stress -- before outward signs of browning or yellowing of leaves become visible," said Elizabeth Middleton, a NASA Goddard-based biologist and a member of the team that created the maps.
The new maps, based on data collected in 2009 from a spectrometer aboard a Japanese satellite called the Greenhouse Gases Observing Satellite (GOSAT), show sharp contrasts in plant fluorescence between seasons. In the Northern Hemisphere, for example, fluorescence production peaked during July, while in the Southern Hemisphere it did in December.
The new findings help confirm previous lab and field experiments that suggest chlorophyll fluorescence should taper off in the fall as the abundance of green foliage declines and stress increases as a result of lower temperatures and less favorable light conditions.'/>"/>
|Contact: Adam Voiland|
NASA/Goddard Space Flight Center