Peat bogs threatened by global change
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Although the surface of peat bogs only covers 3% of the land, it is estimated that
they retain about one-third of the carbon stored in the soils of the
planet.
Photo: EPFL
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Praz-Rodet is one of the four peat bogs studied by the researchers of the WSL Site of Lausanne.
Photo: WSL Site of Lausanne
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Sphagnum have antibiotic properties, which means that micro-organisms decompose them very slowly.
Photo: M. Kaennel Dobbertin, WSL
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ECOS results from a joint-venture, with a joint-professorship, between the EPFL and the Federal Research Institute WSL. The research of the laboratory ECOS is centred on the organization,
functioning and dynamics of terrestrial plant, animal and microbial
communities in relation to ecosystem processes.
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Too much nitrogen is harmful to these fragile
ecosystems, and could lead to the release into the atmosphere of large
quantities of carbon dioxide, as emphasized in an article written by
researchers at the Laboratory of Ecological Systems at EPFL, recently
published in the journal New Phytologist.
Too great a quantity of nitrogen, associated with higher
temperatures, is a serious threat to the existence of peat bogs. Yet the
latter retain a large portion of the carbon stored in soils worldwide,
which would be released into the atmosphere with the destruction of
these fragile environments. This major threat has been highlighted in an
article which was recently published in the journal New Phytologist,
written by Alexandre Buttler, professor at the Laboratory of Ecological
Systems at EPFL, in cooperation with Luca Bragazza, professor at the
University of Ferrara in Italy and at the WSL site in Lausanne. Within
the framework of a consortium of scientists created to better understand
the challenges associated with peat, they have compiled and
cross-referenced the results of 29 studies conducted in 14 countries in
North America and Eurasia.
Since the end of the Pleistocene era (approx. 12,000 years ago), peat
bogs have had a significant influence on the Earth’s atmosphere.
Although their surface only covers 3% of the land, it is estimated that
they retain about one-third of the carbon stored in the soils of the
planet. Mostly, they result from an accumulation of partly decomposed
organic matter of a type of moss called “sphagnum”.
“These plants have particular characteristics: they have antibiotic
properties, which means that micro-organisms decompose them very
slowly”, explains Alexandre Buttler. These peat-moss bogs are also very
poor in nutrients. Thus, their survival relies essentially on what the
atmosphere can supply them with. Therefore, any qualitative or
quantitative changes in rainfall can seriously modify the capacity of
these sites to absorb CO2 from the atmosphere. As sphagnum cannot
regulate their water content – unlike vascular plants which are more
evolved – they need excess liquid to survive and thrive. A period of
drought could therefore spell the end of them.
So what about the effects of nitrogen, an important element in the
growing process of plants, but which can disrupt the balance between
plants if it is present in too great a quantity in its assimilable form?
As a result of human activities such as fossil-fuel combustion and the
use of fertilizers in agriculture, the quantities of assimilable
nitrogen present at the surface of the Earth have considerably
increased. It’s currently estimated that they have doubled in the last
100 years, leading to changes in the distribution of vegetal species in
the peat bogs, and in particular encouraging the development of vascular
plants to the detriment of sphagnum moss. Because vascular plants
decompose more easily than sphagnum, there is a risk that the peat mass
could diminish rapidly.
“Whereas the increase in nitrogen emissions in an area where it is
scarce encourages the growth of or, at least, does not affect the
production of sphagnum, we have been able to show, on the other hand,
that much higher quantities are harmful to this production, and all the
more so if the region is already laden with it”, continues Alexandre
Buttler.
One of the most unexpected results of this research is that the
increase in the level of nitrogen also interacts with climatic factors.
“We have discovered that higher temperatures further intensify this
negative effect”, adds Luca Bragazza. “Our calculations have shown that
an increasing supply of nitrogen, combined with a warmer climate, could
severely reduce the capacity of peat-moss bogs to trap carbon.”
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