Greenhouse gas (carbon dioxide) is not beneficial to plants, as once thought

[Henk Elegeert]

REPLY TO: D66 at nic.surfnet.nl

Rising carbon dioxide levels may hinder crop
growth<http://www.vancouversun.com/Rising+carbon+dioxide+levels+hinder+crop+growth/3031640/story.html>

Greenhouse gas is not beneficial to plants, as once thought

BY AMINA KHAN, DAILY TELEGRAPH MAY 14, 2010 9:00 PM



So much for a hoped-for bright spot to global warming.

Some biologists had theorized that rising greenhouse gas levels would
encourage plant growth over the long term because of the increased amount of
carbon dioxide in the atmosphere. Plant physiologists from the University of
California, Davis, may have dashed those hopes.

They've shown that too much carbon dioxide, which plants need for energy,
can inhibit a plant's ability to assimilate nitrates -- nitrogen-based
nutrients pulled from the soil that plants use to make enzymes and other
essential proteins.

Without those essential proteins, plant health -- and food quality -- may
suffer, the researchers say in a study published online in the journal
Science.

Scientists had previously observed that a rise in carbon dioxide levels --
39 per cent globally since 1800, according to the Intergovernmental Panel on
Climate Change -- would boost photosynthesis, the sunlight-fuelled process
by which plants make sugar.

But previous studies showed that after an initial spike in sugar-making
activity, photosynthesis appeared to level off, even if the carbon dioxide
rate remained high.

"Here we have this quandary where we thought rising carbon dioxide levels
might actually have some benefit, but it proves to be wrong. . . . Over a
period of time, be it weeks or years, that stimulation disappears," said
lead author Arnold Bloom, a professor in the department of plant sciences at
UC Davis.

Other studies showed that after plants were exposed to excess carbon
dioxide, their protein content also dropped.

In a series of five experiments, Bloom and his colleagues found an
explanation. The team exposed plants to high carbon dioxide (or low oxygen),
fertilized them with nitrates and tracked how much nitrogen they
successfully incorporated into their systems.

In each case, the researchers found that the more carbon dioxide exposure,
the less plants were able to assimilate nitrogen. Without enough nitrogen,
the plants could not make as many proteins, including those enzymes used in
photosynthesis -- and thus, would be unable to take advantage of all that
extra carbon dioxide in the air anyway.

The findings have significant implications for agriculture, biologists said.

They suggest that, as global warming continues and carbon dioxide levels
rise, food may become poorer in quality and less nutritious, and farmers may
have to worry about lower-quality crop yields that could perhaps be more
prone to pest infestations (as plant eaters may have to eat more to get the
same nutritional value as before).

The study "has some very important real-world implications," said Harvard
University plant physiologist Noel Michele Holbrook, who was not involved in
the study.

"How do we think about the idea of breeding for more productive crops, and
what sorts of attitudes for breeding are going to pay off in the long run?
We're facing really important challenges in terms of food production and
quality of food."

... "

... according to the Intergovernmental Panel on Climate Change?

Wat neemt 'the Intergovernmental Panel on Climate Change' zoal nog meer aan
en waarvoor het bewijs ten ene male ontbreekt?

Henk Elegeert

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