[NAFEX] nafex Digest, Pesticides Disrupt Nitrogen Fixation
oowonbs at netscape.net
oowonbs at netscape.net
Thu Jan 3 17:56:28 EST 2008
This was worth it...
Cariage returns added, deleted.
Poor, but readable.
From: Hilborn.E at epamail.epa.gov
Subject: [NAFEX] Pesticides Disrupt Nitrogen Fixation
Interesting news from the journal Environmental Health Perspectives
PesticidesDisruptNitrogenFixation Talkaboutaviciouscycle. Some
suppressnitrogen-fixingbacteria fromreplenish ingnatural
nitrogenfertilize rinsoil, resultinginlower cropyields,
stuntedgrowth, andanever-grea terneedfor additivestoboost
production.This previously unrecognized effectstems
frompesticides interferingwith flavonoid signaling from leguminous
alfalfa, peas,and soybeans tosoil bacteria thatfix nitrogen.
"People assume that endocrine disruptionby pesticides occurs only in
humans and animals with estrogen receptors
,but we find thereare nontradit ional targets affected by pesticide
Fox,a postdoctoral researcher at the Center for
Ecology and Evolutionary Biology at the
University of Oregon.
Plants produce chemicals ,many that are structura lly similar to
phytoestrogens, that attract
Rhizobium soil bacteria to their root systems toform nodules for
nitrogen fixation. Inside the
nodules, the bacteria convert atmospheric nitrogen into the natural
fertilizer ammonia. These
symbiotic soil bacteria respond to plant-produced flavonoid molecules
through nodulationD (NodD) receptors ,which
act similarly to estrogen receptors in vertebrat es. In theMay 2004
issue of EHP,Fox and colleagues reported astudy using Sinorhizo bium
a soil bacterium that fixes nitrogen in symbiosis with alfalfa.
The researchers found that the organochl orine pesticides
pentachlo rophenol (PCP)and methyl parathion atlevels foundin farm
NodD signaling by90% and that DDTcut signaling by45%.
In recent greenhouse experiments, Fox and colleague sat Tulane
University treated alfalfa seeds inoculate dwithS. meliloti withPCP,
methyl parathion ,and DDT,
which are found in soil after farmers spray crops, especially in
countries where these pesticides have not been banned.
Sixweeks after treatment,
PCP-treated alfalfa plants produced no nodules, and plant yields fell
to 17% compared with control
plants not treated with pesticides. Methyl parathion and DDT reduced
nodule numbers and plant yields by about half.The
researchers estimate that the amount of inhibition measured in this
experiment could translate in real-world
conditions to a one-third loss of plant yield each growing season. The
results, published 12June 2007in
the Proceedings of the National Academy of Sciences, indicate
that pesticide residues in soil could not only reduce harvest yields,
but also increase the need for
synthetic fertilizers, thereby raising costs for farmers and
contributing to environmental
pollution. The observations also may explaina trendin the past
40 years toward stagnant crop yields despite record highuse of
pesticides and synthetic fertilizers worldwide.
In unpublished experiments, co-author John McLachlan, director of the
Tulane Center for
Bioenvironmental Research showed that the same three pesticide sdisrupt
NodD signaling in
Rhizobium sp. strain NGR234,a bacterium that fixes nitrogen in
symbiosis with more
than 100 leguminous plants growing in tropical and subtropic alsoils.
"Many of the species that NGR234 nodulatesare trees
and bushes, such as teakand rosewood, that promote vital soil
improvement within nutrient-poor tropical
soils," he says. McLachlan says farmers in poorer countries especially
to lose natural fertilizer because synthethic fertilizers cost so much.
The connection between pesticides and nitrogen fixation
shows that "pristine and natural interactions between bacteria and
plants are being
jeopardized by what we put into the soil," says Ann Hirsch,
molecular biologist at the University of California, Los Angeles.
Similarly, the effects of pesticide son human disease continue to be
documented, with a
report in the October 2007 issue of EHP
linking childhood exposure to DDT with a fivefold higher risk of breast
cancer in women.
"Now we are affecting our agricultural assets,
"Hirsch says, "something people take for granted." Fox plans to test
the effects of pesticide son alfalfa and soybeans
under real-life field
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