Simulated chronic NO3- deposition alters fungal community composition in organic and mineral horizons of northern hardwood forests

Background/Question/Methods

Human activities increasingly result in the widespread deposition of biologically-available N forms into forest ecosystems, with unknown consequences for plant productivity and microbial C cycling.   Multiple lines of evidence indicate that organic matter decomposition has been slowed by 13 years of experimental N deposition (30 kg NO₃^-N ha^-1yr^-1) across a regional network of four mature hardwood forest ecosystems.  We reasoned that this change may be related to effects of N deposition on soil fungi, and that fungal community composition may be altered by chronically high N availability.  General fungal PCR primers spanning both ribosomal ITS regions were used to generate Terminal Restriction Fragment Length Polymorphism (T-RFLP) profiles from O and A horizon environmental DNA samples from May and August of 2007. 
Results/Conclusions

N deposition effects were strongest in the A horizon (P = 0.001), where two TRF classes were positively affected by N deposition, and 6 were negatively affected. Stands were characterized by differing TRF composition patterns, with some TRFs occurring only in particular stands and horizons.  N deposition had no significant main effect on TRF composition in the O horizon; however the relative abundance (relative peak height) of dominant O horizon TRFs were significantly altered by N deposition, and individual sites exhibited idiosyncratic species composition responses, suggesting that species composition strongly affects the potential for significant community effects of NO3- deposition.