Increased soil nitrogen associated with dinitrogen-fixing, terricolous lichens of the genus Peltigera in northern Minnesota

Dinitrogen (N₂)-fixing lichens (cyanolichens) have long been recognized as a source of exogenous N in various ecosystems, yet the effects of nitrogen inputs from these lichens have been little studied. Cyanolichens of the genus Peltigera Willd. are often the dominant members of the earth-dwelling (terricolous) cyanolichen community. They occur in diverse habitats around the globe, but no studies of their influence on soil N have been reported. We conducted field and laboratory investigations with the primary objective of determining whether soil N availability is increased near healthy thalli of terricolous dinitrogen-fixing lichens. We measured available soil N in situ with ion-exchange resin bags, potentially mineralizable N with laboratory incubations, total soil N, and soil temperature. Measurements were taken along transects that extended away from thalli of Peltigera, perpendicular to and parallel to topographic contours. Studies were conducted in ten types of forest across northern Minnesota, including two contrasting sites that represent extremes of habitat for Peltigera. Soil N availability, potentially mineralizable N, and soil %N increased significantly with proximity to healthy thalli of Peltigera (P-values<0.05). Moreover, potential N mineralization was highly correlated with soil %N (R²=0.765). Our results suggest a potential zone of influence that extends 1.5 m from thalli of Peltigera. The data indicate that soil temperature is not a primary factor in these associations.