BIOPLAN POSTING 2001-5-14

David.Duthie@unep.org
Sent by: owner-bioplan@undp.org
05/07/01 09:03 AM

bioplan
David.Duthie@unep.org
Dear BIOPLANNERS,

Plant diversity enhances ecosystem responses to elevated CO2 and nitrogen
deposition

I apologise for being a little slow in broadcasting this important
research, reported in Nature April 12th 2001, but I wanted to see the
original article rather than just run with the press coverage.

Whilst it is always good to have empirical evidence to support the
intuitive feeling that biodiverse systems would be more efficient sinks for
carbon and nitrogen, it is important to realise that this experiment says
little about what is may happen to carbon sequestration responses of
complex natural ecosystms in a greenhouse world.

The experiment investigates the response of different combinations  (1, 4,
9 and 16 species mixtures) of 4 functional groups of grassland plants (C3
grasses, C4 grasses, C3 legumes and C3 non-legume herbs).  The more complex
experimental systems show greater accumulation of carbon and nitrogen, due
to a combination of "multiple-species sampling effects, niche
complementarity and positive species interactions".

What is unclear is the extent to which these effects would continue as more
and more species are added; in other worlds, the issue of how many species
are essential to (real) ecosystem function, and how many are "spare
rivets", remains untested here.

The full title of the paper is:

Relch, P. B. et al (2001)   Plant diversity enhances ecosystem responses to
elevated CO2 and nitrogen deposition.  Nature 410: 809-812.

Please contact me if you would like to see the entire article.

I am off to sequester some carbon in Zambia this coming week , whilst
attending a BPSP thematic workshop on the integration of biodiversity into
EIA procedures.

Best wishes
 

David Duthie

***********************************************************************************************************

Biodiversity Gives Carbon Sinks a Boost

 By Cat Lazaroff

 UPTON, New York, April 13, 2001 (ENS) - The more diverse an  ecosystem,
the better it can serve to absorb carbon dioxide - a  potent greenhouse gas
- from the atmosphere, a new study  suggests. The research has important
implications for ongoing  international negotiations over the best way to
address global climate  change, and the role that so called carbon sinks
should play.

 Biodiversity is an important factor regulating how ecosystems will
respond to increasing atmospheric carbon dioxide, say researchers  from the
U.S. Department of Energy's Brookhaven National Laboratory  and their
collaborators. The team of investigators, led by Peter Reich  of the
University of Minnesota, just released results from a major field  study
that appears in the April 12 issue of the journal "Nature."

 All plants absorb carbon  dioxide as they grow, but  different species
absorb  carbon at different rates - and  different environmental
conditions can also affect how well plants absorb carbon.

 The scientists found that more diverse plant ecosystems were better  able
to absorb carbon dioxide (CO2) and nitrogen, both of which are  on the rise
due to human activities and industrial processes.

 "The key implication of this research is that, in response to elevated
levels of CO2 and nitrogen, ecosystems with high biodiversity will  take up
and sequester more carbon and nitrogen than do ecosystems  with reduced
biodiversity," said Brookhaven plant physiologist David  Ellsworth, one of
the study authors.

 The findings could influence international efforts to control emissions
of greenhouse gases like carbon dioxide. Industrialized countries,
particularly the United States, support the use of carbon sinks -
vegetation that absorbs carbon dioxide - as a mechanism for  reducing the
amount of CO2 added to the atmosphere.

 Critics of carbon sinks argue  that placing limits on industrial  sources
of CO2 is the best  way to reduce carbon  emissions, and emphasizing
carbon sinks could take  attention away from the need  to cut emissions.

 In addition, some fear that nations will advocate replacing old growth
forests - which have largely completed the part of their life span in
which they absorb the most CO2 - with tree plantations or other fast
growing crops. Incentives to create carbon sinks could prove  devastating
to efforts to preserve the planet's remaining pristine  ecosystems.

 The study released this week lends credence to arguments that  intact
ecosystems do a better job of regulating environmental  problems than do
manmade landscapes.

 The experiment, called BioCON - for Biodiversity, CO2 and nitrogen -  is
the first field study to test the idea that plant species diversity
influences the responses of natural ecosystems to elevated CO2 and
nitrogen levels. The project was performed in a scientifically  controlled
grassland environment at the Cedar Creek Natural History  area of the
University of Minnesota, using free air CO2 enrichment  technology.

 This experimental free air CO2 (FACE) technology was developed by
Brookhaven National Laboratory to study the effects of extra CO2 on  plants
in their natural environment, rather than in greenhouses or  other
enclosures.

 Each FACE facility consists of  six 20 meter diameter  experimental plots,
each  encircled by a ring of five foot  tall vertical pipes capable of
releasing different amounts of  CO2. Computers monitor the wind speed, wind
direction and CO2 level  within each ring, and adjust the release of CO2 to
achieve the  atmospheric concentration that is expected to occur 50 years
from  now.

 In the BioCON study, the six rings were each subdivided into  experimental
plots measuring two by two meters. In 1997, these  subplots were planted
with different numbers and varieties of  grassland plant species, creating
a range of species diversities.

 The experimental plots within three of the rings received no additional
CO2, while the other three rings were bathed in CO2 that was about  50
percent above current concentrations. Beginning in 1998, half the  plots
received additional nitrogen, comparable to the high rates of  nitrogen
that are deposited in industrialized regions.

 At the end of both the 1998 and 1999 growing seasons, the  scientists
measured the total amount of plant matter, known as  biomass, per square
meter in each plot. Biomass is an indicator of the  amount of carbon the
plants accumulate through photosynthesis, the  process by which green
plants use CO2, water and sunlight to grow.

 Nitrogen, an important plant nutrient, is absorbed from the soil to
become part of the biomass.

 The researchers learned that elevated levels of CO2 and nitrogen  resulted
in increased biomass when compared with plots exposed to  ambient levels of
CO2 and nitrogen. The effect, however, was  greatest in plots with high
biodiversity as compared to those with  fewer species.

    "These findings     suggest that     protecting biodiversity  worldwide
will contribute to safeguarding the capacity of ecosystems  to capture a
larger fraction of additional carbon and nitrogen entering  our environment
due to industrial processes," said Brookhaven  ecologist George Hendrey,
who led development of the FACE system  and is another coauthor on the
current study.

 One reason for the greater uptake of CO2 and nitrogen in biodiverse  plots
may be that the different plant species bloom and go to seed at  different
times. The plot is therefore absorbing CO2 and nitrogen over  the entire
growing season, rather than just part of it.

 Other interactions among the plant species may also be contributing  to
the effectiveness of the biodiverse plots as carbon sinks, the  scientists
said.

  © Environment News Service (ENS) 2001. All Rights Reserved.
 
 

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