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Impacts of Organic and Conventional Crop Management on Diversity and Activity of Free-Living Nitrogen Fixing Bacteria and Total Bacteria Are Subsidiary to Temporal Effects

Lookup NU author(s): Dr caroline Orr, Professor Carlo Leifert, Dr Julia Cooper



A three year field study (2007-2009) of the diversity and numbers of the total and metabolically active free-living diazotophic bacteria and total bacterial communities in organic and conventionally managed agricultural soil was conducted using the Nafferton Factorial Systems Comparison (NFSC) study, in northeast England. Fertility management appeared to have little impact on both diazotrophic and total bacterial communities. However, copy numbers of the nifH gene did appear to be negatively impacted by conventional crop protection measures across all years suggesting diazotrophs may be particularly sensitive to pesticides. Impacts of crop management were greatly overshadowed by the influence of temporal effects with diazotrophic communities changing on a year by year basis and from season to season. Quantitative analyses using qPCR of each community indicated that metabolically active diazotrophs were highest in year 1 but the population significantly declined in year 2 before recovering somewhat in the final year. The total bacterial population in contrast increased significantly each year. It appeared that the dominant drivers of qualitative and quantitative changes in both communities were annual and seasonal effects. Moreover, regression analyses showed activity of both communities was significantly affected by soil temperature and climatic conditions.

Publication metadata

Author(s): Orr CH, Leifert C, Cummings SP, Cooper JM

Publication type: Article

Publication status: Published

Journal: PLoS One

Year: 2012

Volume: 7

Issue: 12

Print publication date: 01/12/2012

Date deposited: 27/02/2013

ISSN (electronic): 1932-6203

Publisher: Public Library of Science


DOI: 10.1371/journal.pone.0052891


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Funder referenceFunder name
Nafferton Ecological Farming Group
Northumbria University Research Development Fund
NPD/JMD/08/72The Yorkshire Agricultural Society
NUE CROPS EU-FP7 222-645European Community under the Seventh Framework Programme for Research, Technological Development and Demonstration Activities, for the Integrated Project