Forests are known to be carbon sinks, but did you know that trees also exchange large quantities of the greenhouse gas with their neighbors, too?
Using a type of modified carbon dioxide, botanists from the University of Basel were able to track the gas as it was taken up by roots of various trees in a forest near Basel, including trees of different species.
Researchers found that this extensive carbon trade among trees is facilitated via symbiotic fungi in the forest soil.
"Evidently the forest is more than the sum of its trees," said Professor Christian Körner, one of the study researchers from the University of Basel.
Körner and colleagues Tamir Klein and Rolf Siegwolf of the Paul Scherrer Institute used a construction crane and a network of fine tubes to shower the crowns of 120-year-old and 40-meter tall spruce trees with carbon dioxide that carried a label.
Plants take up carbon dioxide from the air through processes of photosynthesis, which are then converted into sugar to build cellulose, wood pulp (lignin), protein and lipid - the building blocks of plants.
While it is well known that this resulting sugar is transported from a tree's leaves to its branches, stems, roots and symbiotic fungi below ground, the recent study suggests that this sugar export goes further than previously thought.
Compared to normal air, the carbon dioxide that the researchers used contained less of the rare and heavier 13C atom, which made no difference for the trees.
Using an atomic mass spectrometer, the researchers were able to trace the movement of the carbon as it was taken up by photosynthesis from the crown of the tree down to its root tips.
The labeled carbon was found not only in the roots of marked spruce trees, but also in the roots of neighboring trees that had not been flooded with the modified carbon. Surprisingly, it was even taken up in the roots of trees from other species, such as beech, pine or larch tree.
However, the only way in which carbon can be exchanged between completely unrelated tree species is by the network of tiny fungal filaments in the shared underlying symbiotic fungi.
This discovery, researchers say, came as "a big surprise" and brings to light the role of soil fungi in forests.
The findings were published in the April 15 issue of the journal Science.
