Towards a molecular understanding of N cycling in northern hardwood forests under future rates of N deposition

• Published in: Soil biology & biochemistry 2013-11, Vol.66, p.130-138
• Main Authors: Freedman, Zachary, Eisenlord, Sarah D., Zak, Donald R., Xue, Kai, He, Zhili, Zhou, Jizhong
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; ammonification; Archaea; Bacteria; Biochemistry and biology; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Climate change; combustion; community structure; denitrification; Dispersion; fertilizers; forest stands; fossil fuels; Fundamental and applied biological sciences. Psychology; genes; hardwood forests; microarray technology; microbial communities; N cycle; N deposition; nitrate reduction; nitrification; nitrogen fixation; organic matter; Physics, chemistry, biochemistry and biology of agricultural and forest soils; soil; soil microorganisms; Soil science; species diversity
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2013.07.010

The combustion of fossil fuels and fertilizer use has increased the amount of biologically available N over the last 150 years. Future rates of atmospheric N deposition may slow organic matter decay and alter microbial community composition and function. However, our understanding of how anthropogenic N enrichment may alter the physiological mechanisms by which soil microorganisms assimilate and cycle N in soil are largely unknown. Since 1994, we have experimentally increased NO3 deposition to replicate (n = 4) northern hardwood forest stands across a 500-km climatic gradient in the Great Lakes region of North America. Our goal was to examine how functional genes mediating N-cycle processes in soil microbial communities have responded to experimental N deposition using the functional gene microarray, GeoChip 4.0. Experimental N deposition decreased the abundance and richness of key protein-coding genes in Archaea and Bacteria responsible for N fixation, ammonification, denitrification and assimilatory nitrate reduction; the same was true for bacterial genes mediating nitrification and dissimilatory nitrate reduction. However, the extent to which experimental N deposition decreased abundance and richness was site-specific, which was revealed by a significant site by treatment interaction. Experimental N deposition also caused a community composition shift via dispersion (increased β-diversity) in archaeal and bacterial gene assemblages. In combination, our observations suggest future rates of atmospheric N deposition could fundamentally alter the physiological potential of soil microbial communities. •We examined the effect of elevated N deposition on N-cycling Bacteria and Archaea.•A decrease in abundance and α-diversity of N-cycling assemblages was noted.•N-cycling assemblages exhibited increased β-diversity under increased N deposition.•Assimilation, denitrification, and nitrification potential were especially affected.