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ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Publications at this Location » Publication #83928


item Ibekwe, Abasiofiok - Mark
item Kennedy, Ann

Submitted to: Federation of European Microbiological Societies Microbiology Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soil microbes can have a profound effect on plant growth and agroecosystems; however, a greater understanding of microbial communities is needed to enhance the use of microbes in agriculture. Despite the potentially beneficial microbial communities that develop in the soil surrounding the root, our knowledge of the physiological traits in microbes that confer rhizosphere competence is limited. A better understanding of rhizosphere communities will help develop methods of controlling or introducing harmful or beneficial bacteria to soil. Soil populations of bacteria cannot be cultured with most current techniques, and thus changes in the structural and functional relationships in the microbial community of agricultural soils is difficult to measure without disturbing the population. Culture techniques also are limited, depend on the media, and can underestimate the resident population. To better understand microbial diversity in agricultural soils, our objectives were to determine whether there are differences in community structure of different crops within a landscape and to assess differences in microbial diversity between the two agricultural soils. Our molecular approach was very helpful in understanding differences in rhizosphere and nonrhizosphere of different crops within a landscape. This research will better assist in the development microbial inoculants and management to enhance plant growth in agroecosystems.

Technical Abstract: Fatty acid methyl ester (FAME) profiles from soil can be used to describe soil microbial community structure without reliance on culturing soil microorganisms. To verify changes in soil microbial community structure with fatty acid fingerprints, field and greenhouse experiments were conducted. Soil samples were collected from Ritzville and Palouse silt loam soils for fatty acid analysis. Soil samples from wheat, barley, pea, jointed goatgrass and downy brome rhizospheres were also collected from Palouse soil for fatty acid analysis. Principal component (PCA) and factor analyses of FAME profiles were used to identify similarities and differences between FAME of the two soils with different climatic conditions and agricultural practices. PCA of the two soils explained 46% of the variance on PC1, which accounted for Palouse soil compared to Ritzville soil with 25% of the variance on PC2. Factor analysis showed that rhizosphere microbial communities from various plant species may differ depending on the plant species and the environment. Presence of Gram positive bacteria as identified by 15:0 Anteiso/Iso and 17:0 Anteiso/Iso peaks were similar between rhizosphere and nonrhizosphere soils. Gram negative bacteria characterized by short chain hydroxy acids (10:0 3OH and 12: 3OH) as well as cyclopropane acids (17:0 w? Cyclo) were higher in rhizosphere soil than nonrhizosphere. This indicates a possible shift in the bacterial community to a more Gram negative bacteria and fewer Gram positive bacteria in the rhizosphere of plants species studied. On the basis of our data, FAME profile analysis is a technique that can assess the relative similarities, differences, and shift in microbial community structure of complex environments.