Every year, trees and plants across the world
absorb a vast amount of carbon dioxide from the
But a new study suggests this massive carbon
sink could instead become a source of carbon dioxide by the end of
This means we might not be able to rely on
plants soaking up our emissions for much longer, the lead author
tells Carbon Brief.
Extra carbon dioxide
Through photosynthesis, plants convert carbon
dioxide, water and sunlight into the fuel they need to grow,
locking up carbon in their branches, stems
and leaves in the process.
Research suggests that as human-caused
carbon dioxide emissions accumulate in the atmosphere, plants will
grow more quickly because the rate of photosynthesis speeds up.
This is called 'carbon dioxide fertilisation'.
argument is sometimes used in parts of the
media to suggest that additional carbon dioxide is beneficial for
the Earth as extra food for plants.
But research published this week in Nature
Geoscience suggests that plants won't have enough
nutrients to make full use of the extra carbon dioxide in the
atmosphere. So any benefits will be limited, say the
Plants need the right mix of nutrients to grow.
Two of the most important nutrients are nitrogen and phosphorus.
But there isn't an endless supply in soils for plants to use, lead
author Dr Will
Wieder, from the National Centre for Atmospheric
Research in Colorado, tells Carbon Brief:
"Many ecosystems appear
to be co-limited, meaning that both nitrogen and phosphorus are
important for plant growth. There are places where one element or
the other may be slightly more limiting, but at the end of the day
plants need both to build roots, leaves and wood. This is why many
fertilizers used in gardens and farms come with both nitrogen and
While nitrogen is abundant in the air we
breathe, most plants can only take it up from the soil. Nitrogen
gets into the soil by being 'fixed' from the air by microbes and
certain plants, such as soy, Wieder says. Phosphorus primarily
originates from rocks, and reaches the soil when they are worn down
by the weather.
Nutrients can come from a little further afield
as well, Weider adds:
"Both nitrogen and
phosphorus can be moved around and transported through the
atmosphere as dust or air pollution. The subsequent deposition of
nitrogen and phosphorus also can contribute new nutrients to an