( >Fox began the project as a doctoral st...)Pesticides choke pathway for nature to produce nitrogen for crops

>Fox began the project as a doctoral student with John A. McLachlan, director of the Center for Bioenvironmental Research at Tulane University. She is working at the University of Oregon as a National Institutes of Health and National Research Service Award postdoctoral fellow under Joe Thornton, a professor of biology who focuses on phylogenomics and nuclear receptor genes.

Fox and colleagues began detailing their findings in the journal Nature (2001) and Environmental Health Perspectives (2004), testing more than 50 chemicals, including pentachlorophenol (PCP), in in-vitro assays. The paper in PNAS reports their in-vivo findings using real plants and bacteria.

None of the chemicals used in the research, including PCP, proved to be toxic to either the plants or bacteria, Fox said, "but PCP was unique in that it inhibited both seed germination and nitrogen fixation." More than 20 commonly used agricultural chemicals shared the same mechanism of action as PCP, but with varying amounts of signal disruption.

Fox, McLachlan and colleagues, in their PNAS paper, pointed to two published studies from 2000 that had found significant declines in both crop yield per unit of synthetic nitrogen fertilizer added and also a significant decline in overall symbiotic nitrogen fixation.

The most common explanation for the observations is an overuse of agrichemicals applied to legume crops. That practice sets up "a vicious cycle," Fox said, because it reduces a legume crop's natural need for nitrogen fixation but leaves a shortage of natural nitrogen in the soil for the next year's crop to utilize. Thus, she said, there is the need for yet more fertilizer.

Other reasons, Fox said, have been poor soil quality due to overuse, which strips nutrients such as nitrogen and phosphorous from the soil, and to tillage, which interrupts root structures and disturbs the nitrogen-fixing bacteria when soil is turned.

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Source:University of Oregon

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