Carbon flux in a subalpine spruce-fir forest: pulse release fromHylocomium splendensfeather-moss mats

Mature subalpine spruce-fir forests in western Alberta are often characterized by extensive feather-moss mat coverage of the forest floor surface. The ecosystem role of these mats has been described as one of a nutrient sink because of their ability to assimilate solutes from throughflow solutions and their role as a catchment area for litterfall and detritus. These bryophyte mats are subject to recurring episodes of wetting and drying during the summer months. We examined the potential for pulse release to throughflow solution of previously sequestered carbon held by Hylocomium splendens (Hedw.) B.S.G. During rehydration, pulse release, measured as total organic carbon (TOC), reached 1544 mg·m -2 . At a stand level basis this represents up to 15 kg·ha -1 pulse release of readily soluble carbon from the live green layer of H. splendens moss mats during each rewetting event. Control throughflow collectors, where moss mats were replaced by an inert mulch layer, indicated that from 23 to 75% of this pulse release originated in the moss mats. High intensity rain events resulted in larger net TOC and K release, as did a pretreatment history of rapid drying of H. splendens fronds. These findings suggest that feather-moss mats may function, in part, as ecosystem capacitors, sequestering nutrients and carbon at low concentrations from atmospheric sources, which are later released at higher concentrations during rewetting events.Key words: bryophyte, pulse release, carbon cycling, moss, nutrient cycling, montane forest.