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

Abstract

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 N2-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–1in 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–1of newly fixed N that would otherwise be unavailable in mature sub-boreal forests.