Chronic nitrogen deposition and the composition of active arbuscular mycorrhizal fungi

a b s t r a c t A growing body of evidence indicates that atmospheric nitrogen (N) deposition can alter the composition and function of arbuscular mycorrhizal fungi (AMF) associated with plant roots. We studied the com- munity of AMF actively transcribing ribosomal genes in the forest floor of northern hardwood forests dominated by sugar maple (Acer saccharum Marsh.) that have been exposed to experimental N deposi- tion since 1994 (30 kg NO3 − -N ha −1 year −1 ). Our objective was to evaluate whether previously observed declines in AM root infection and mycelial production resulted in a compositional shift in the AM fungi actively providing resources to plant symbionts under chronic N deposition. To accomplish this task, we cloned and sequenced the LSU of reverse-transcribed AM fungal rRNA extracted from the forest floor under ambient and experimental N deposition treatments. We found that experimental N deposition did not alter the active community of AMF or AMF diversity, but we did observe a significant decrease in rare taxa under chronic N deposition. Our results indicate that chronic N deposition, at levels expected by the end of this century, can exert a moderate influence on the composition and abundance of AMF associated with plant roots in a wide-spread forest ecosystem in the northeastern North America.