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Applied and Environmental Microbiology, October 2009, p. 6240-6248, Vol. 75, No. 19
0099-2240/09/$08.00+0 doi:10.1128/AEM.01126-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Afforestation Alters the Composition of Functional Genes in Soil and Biogeochemical Processes in South American Grasslands
,
Sean T. Berthrong,1*
Christopher W. Schadt,2
Gervasio Piñeiro,3,4 and
Robert B. Jackson1,4
University Program in Ecology, Duke University, Durham, North Carolina 27708,1 Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831,2 Laboratorio de Análisis Regional y Teledetección, IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, CONICET, Buenos Aires, Argentina,3 Department of Biology and Nicholas School of the Environment, Duke University, Durham, North Carolina 277084
Received 15 May 2009/ Accepted 4 August 2009
Soil microbes are highly diverse and control most soil biogeochemical reactions. We examined how microbial functional genes and biogeochemical pools responded to the altered chemical inputs accompanying land use change. We examined paired native grasslands and adjacent Eucalyptus plantations (previously grassland) in Uruguay, a region that lacked forests before European settlement. Along with measurements of soil carbon, nitrogen, and bacterial diversity, we analyzed functional genes using the GeoChip 2.0 microarray, which simultaneously quantified several thousand genes involved in soil carbon and nitrogen cycling. Plantations and grassland differed significantly in functional gene profiles, bacterial diversity, and biogeochemical pool sizes. Most grassland profiles were similar, but plantation profiles generally differed from those of grasslands due to differences in functional gene abundance across diverse taxa. Eucalypts decreased ammonification and N fixation functional genes by 11% and 7.9% (P < 0.01), which correlated with decreased microbial biomass N and more NH4+ in plantation soils. Chitinase abundance decreased 7.8% in plantations compared to levels in grassland (P = 0.017), and C polymer-degrading genes decreased by 1.5% overall (P < 0.05), which likely contributed to 54% (P < 0.05) more C in undecomposed extractable soil pools and 27% less microbial C (P < 0.01) in plantation soils. In general, afforestation altered the abundance of many microbial functional genes, corresponding with changes in soil biogeochemistry, in part through altered abundance of overall functional gene types rather than simply through changes in specific taxa. Such changes in microbial functional genes correspond with altered C and N storage and have implications for long-term productivity in these soils.
* Corresponding author. Mailing address: Duke University, Biology Department, Campus Box 90338, Durham, NC 27708. Phone: (919) 613-8214. Fax: (919) 660-7293. E-mail: sberthrong{at}gmail.com
Published ahead of print on 21 August 2009.
Supplemental material for this article may be found at http://aem.asm.org/.
Applied and Environmental Microbiology, October 2009, p. 6240-6248, Vol. 75, No. 19
0099-2240/09/$08.00+0 doi:10.1128/AEM.01126-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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