ARS | Publication request: Soil Rhizosphere Microbial Communities and Enzyme Activities under Organic Farming

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 17, 2011
Publication Date: July 21, 2011
Citation: Gardner, T., Acosta Martinez, V., Senwo, Z., Dowd, S. 2011. Soil Rhizosphere Microbial Communities and Enzyme Activities under Organic Farming[abstract]. Enzymes in the Environment. July 17-21, 2011, Bad Nauheim, Germany.

Technical Abstract: This study investigated the activities of ß-glucosidase (C cycling, ß-glucosaminidase (C and N cycling), acid phosphatase (P cycling) and arylsulfatase (S cycling) under lettuce (Lactuca sativa), potato (Solanum Tuberosum), onion (Allium cepa L), broccoli (Brassica oleracea var. botrytis) and Tall fescue grass (Festuca arundinacea) in an organic production system in Alabama. Soil microbial communities were characterized using fatty acid methyl ester (FAME) and pyrosequencing techniques. The soil was a silt loam with pH of 6.53 and 2.25 g total C kg-1 soil. Some of the trends found in the microbial community structure of the plant rhizospheres may explain the results of enzyme activities. For example, the following trend in fungal:bacterial ratios of soil microbial communities were found: pasture (1.40) > broccoli (0.92) and potato (0.93)> onion (0.83) and lettuce (0.75). The lowest fungal (345.6 nmols g-1 soil) and bacterial (417.6 nmols g-1 soil) FAME concentrations were found under onion rhizosphere, which also showed the lowest microbial biomass C (192 mg C kg-1soil) and lowest enzyme activities. A distinct trend for onion rhizosphere with pyrosequencing was the high abundance of bacteria in the Streptomycetaceae family (up to 31%) compared to other rhizospheres. This group of bacteria is known to produce secondary metabolites which perhaps modify microbial communities (i.e., antagonistic activities) under onion. Greater ß-glucosidase activity (up to 40%) was found under potato rhizosphere compared to the other plant rhizospheres. Further, pyrosequencing revealed that potato rhizosphere sustains a higher abundance of bacterial families of ß-Proteobacteria (i.e., Rhodocyclaceae, Comamonadaceae and Oxalobacteraceae), which are important in C cycling. ß-glucosaminidase activity was higher under pasture, potato and broccoli rhizospheres compared to onion and lettuce, which are in agreement with fungal:bacterial ratio trends. Acid phosphatase activity was highest (up to 35%) under broccoli compared to the other plant rhizospheres, which may suggest differences in P cycling among the plant rhizospheres. The differences found in microbial community structure and enzyme activities in this organic farming system can have implications in soil functioning and health, and the nutritional value of crops.