Tree Range

Professor Ingo Ensminger and PhD candidate Chris Wong
Wednesday, November 16, 2016 - 1:31pm
Carla DeMarco
U of T Mississauga researchers involved in large-scale, cutting-edge collaboration that looks at pigment shifts in evergreen trees using satellites

Scientists have been using earth-observation satellites for a while, but these days they are picking up a lot more than weather patterns and pollution.

This is a most welcome technology for Department of Biology Professor Ingo Ensminger and Chris Wong, a PhD candidate in Ensminger’s lab. Working together with an international team of researchers, they have developed an innovative way to use satellite-sensor data to track photosynthetic activity in northern evergreen forests.

“Photosynthesis is a process whereby plants use the energy that they absorb from sunlight to convert carbon dioxide [CO2] the atmosphere and water into sugars to produce organic matter,” says Ensminger.

“Photosynthesis is sensitive to high temperature and drought, and as climate changes, plants respond.”

“We are eager to understand how northern forests will respond to changing climate because they take up some 14 per cent of the Earth’s land and exchange massive amounts of carbon dioxide with the atmosphere through photosynthesis,” says Ensminger. He explains that this “breathing” of the forests varies on a daily and seasonal basis, as photosynthetic carbon uptake requires light during the day and warm temperatures during the growing season.

Variations in photosynthesis is much easier to track in deciduous trees because of the visible cycle in the budding of the leaves, the change in leaf colour from green to yellow and brown, and their subsequent falling off. According to Ensminger satellites can easily track this seasonal greening of large forest areas.

However, evergreen conifers, which Ensminger says are “important regulators of global climate,” have been a long-standing challenge.

“Large-scale monitoring of the seasonal greening of northern evergreen forests is difficult because their leaves remain green year-round,” explains Wong.

“They undergo changes in leaf color that are ‘invisible’ to the human eye and therefore their leaf colour does not reveal easily when photosynthetic carbon dioxide uptake is paused for the winter.”

By way of response, Ensminger, Wong and their colleagues have identified two different satellite bands that can track the seasonal changes of needle pigments in evergreens. These pigments are green chlorophylls and yellow carotenoids, which are linked to seasonal changes in photosynthetic activity and can reflect the onset and the winter pause of photosynthesis. Wong explains that “this spectral signature can now be used by earth-observation satellites to better track the breathing of these forests and facilitate observing and understanding global climate.”

This novel way to track photosynthesis in evergreens has the potential to improve the assessment of boreal forests’ health amid climate change, and the research team’s findings were published last week in the Proceedings of the National Academy of Sciences (PNAS).

The researchers are excited about this new resource, because they will be able to further investigate two particular theories amid climate change: whether plants absorb more CO2 and thus slow down climate change, or if they release CO2 and accelerate climate change.

Professor John Gamon from biological sciences at the University of Alberta is the lead researcher on the project, and collaborators come from various institutes including U of T, University of North Carolina, University of Maryland, Baltimore County, University of Nebraska-Lincoln, Center for Ecological Research and Forestry Applications (Spain), NASA, and the U.S. Forest Service.