However, in September, use of organic crop protection protocols led to more activity among the nitrogen fixing bacteria as compared to when conventional pesticides were used, says Orr, suggesting that "nitrogen-fixing bacteria are particularly sensitive to the toxic effects of chemical pesticides."
It turns out the prior crop had a major influence on nitrogen-fixing activity, says Orr. Beans, legumes, commonly used in organic rotations have symbiotic relationships with bacteria that fix nitrogen for them; hence, they deplete less nitrogen from the soil, and the higher concentration of nitrate and ammonium suppresses the population of free-living nitrogen fixers. Conversely, soil growing barley (or other non-leguminous crops) would be relatively depleted of nitrogen, and so nitrogen-fixing bacteria would thrive, says Orr, remaining in higher numbers the following year.
The researchers assayed the population density of nitrogen fixing bacteria by measuring the concentration of nifH, the most conserved of the genes involved in nitrogen fixation. They sampled the density of all bacteria via 16S ribosomal RNA. The ribosomes are the machinery that reads ribonucleic acid to manufacture proteins.
(C.H. Orr, A. James, C. Leifert, J.M. Cooper, and S.P. Cummings, 2011. Diversity and activity of free-living nitrogen-fixing bacteria and total bacteria in organic and conventionally managed soils. Appl. Environ. Microbiol. 77:911-919.)
Researchers Model Fetal-To-Adult Hemoglobin Switching: Important Step Towards Cure For Blood Diseases
Researchers have engineered mice that model the switch from fetal to adult hemoglobin, an important step towa
|Contact: Jim Sliwa|
American Society for Microbiology