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–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.

Importance of Arboreal Cyanolichen Abundance to Nitrogen Cycling in Sub-Boreal Spruce and Fir Forests of Central British Columbia, Canada

“…Low Cyano sites had lower average cyanolichen abundances and diversities and were located within 10-20 km of the High Cyano sites at a slightly higher mean elevation of 850 m a.s.l. and similar mean summer temperature and relative humidity of 10.8 ± 5.3 °C and 78%, respectively [8]. Soils at all sites were Orthic Humo-Ferric Podzols formed from sandy-colluvial materials at the High Cyano sites and from sandy-skeletal glaciofluvial materials at the Low Cyano sites.…”

“…High Cyano sites were in "sub-boreal spruce" (SBS) 'wk1' and the 'vk' subzones (BC Biogeoclimatic Ecosystem Classification scheme) with a mean elevation of 680 m above sea level (a.s.l. ), mean summer temperature of 11.8 ± 5.3 °C and relative humidity of 78% [8]. Low Cyano sites had lower average cyanolichen abundances and diversities and were located within 10-20 km of the High Cyano sites at a slightly higher mean elevation of 850 m a.s.l.…”

“…Soils at all sites were Orthic Humo-Ferric Podzols formed from sandy-colluvial materials at the High Cyano sites and from sandy-skeletal glaciofluvial materials at the Low Cyano sites. Average precipitation in the ecotonal study area is approximately 897 mm per year [8].…”

“…For example, the removal of lichens from an oak forest system had no effect on tree growth [7]. Thus, while atmospheric N contributions from cyanolichens are observed in sub-boreal spruce and fir ecosystems [8], it is difficult to predict the nature of combined cyanolichen and host conifer tree ecological interactions (i.e., mutualistic to competitive) over tree to forest spatial and as well as temporal scales.…”

“…To do this, we measured the 15 N: 14 N, %N of host tree (i.e., conifer) foliage, host tree epiphytic lichen functional groups and organic and mineral soil horizons under the tree crowns at sites containing variable amounts of cyanolichen tripartite (i.e., L. pulmonaria) and bipartite lichens from relatively low to high levels. We hypothesized that sub-boreal forest trees with high cyanolichen abundance should have higher needle %N reflecting the greater inputs of biologically fixed-N into these systems [8,31]. Knowledge obtained from this study should provide valuable information on the functional importance of epiphytic (N2-fixing) cyanolichens to the N-status of wet sub-boreal conifer ecosystems of central BC.…”