Decomposition and nutrient release from four epiphytic lichen litters in sub-boreal spruce forests

Epiphytic lichens are highly abundant in many sub-boreal forests and may be important components of nutrient cycling. Decomposition of, and nutrient release from, two cyanolichens (with N-2-fixing cyanobacterial partners) and two chlorolichens (with green-algal partners) were quantified to estimate N inputs from epiphytic lichen litter in late-seral forests. Initial decay rates were strongly correlated with initial % N; the high-N cyanolichen litters (Nephroma helveticum Ach. and Lobaria pulmonaria (L.) Hoffm.) lost 26% more mass than the lower-N chlorolichen litters (Alectoria sarmentosa (Ach.) Ach. and Platismatia glauca (L.) W. L. Culb. & C. F. Culb.) over the first 4 months. Morphological characteristics also influenced decay, as decomposition of the hair chlorolichen (A. sarmentosa) was similar to that of the foliose cyanolichens, despite an N concentration that was 87% lower. N was immediately released from cyanolichen litters and retained in chlorolichen litters. After 24 months of decay, N concentrations remained highly divergent with 22-27 and 7-8 mg N.g(-1) in cyanolichen and chlorolichen litter, respectively. Cyanolichen litter represents 0.1%-2.3% of the total aboveground litter biomass and 0.5%-11.5% of the total N input from aboveground litterfall. Decomposition of cyanolichen litter is estimated to release up to 2.1 kg N.ha(-1).year(-1) of newly fixed N that would otherwise be unavailable in mature sub-boreal forests.