PARENT SESSION
Wednesday, August 9, 8:00-11:30 am
COS 56 - Soil ecology
Mississippi, Mezzanine Level, Cook Convention Center
Presiders: S Baer and J Six

Chronic NO₃^- deposition reduces basidiomycete laccase gene abundance in northern hardwood forests.

Hassett, John^*,1, Zak, Donald¹, Pregitzer, Kurt², ¹ University of Michigan, Ann Arbor, MI² Michigan Technological University, Houghton, MI

ABSTRACT- Human activities increasingly release biologically-available N into the biosphere, with unknown consequences for soil microbial communities. We tested the hypothesis that chronic atmospheric N deposition will reduce the abundance of white-rot basidiomycetes, a dominant group of lignin-decomposing soil fungi, due to suppression of lignolytic capacity by high inorganic N concentrations. DNA was extracted from litter and mineral soil across an experimental network of four mature hardwood forest ecosystems that have received chronic N deposition (30 kg NO₃^--N ha^-1 yr^-1) since 1994. Quantitative PCR of basidiomycete laccase, a gene encoding a key lignolytic enzyme, revealed that experimental N deposition had reduced the abundance of this gene by 15% in soil and 10% in litter, a response consistent with observed declines in lignolytic enzyme activity. Length-heterogeneity profiles (LH-PCR) of laccase amplicons revealed significant differences in the composition of lignin-degrading basidiomycetes between litter and mineral soil; however chronic N deposition did not affect the composition of basidiomycete communities in litter or soil. Our results suggest that anthropogenic N deposition can suppress an entire community of lignin decomposing soil fungi, potentially altering the course of organic matter decomposition and ecosystem C cycling.

Key words: anthropogenic nitrogen, soil ecology, hardwood forest