The study examined the functional role of leaf litter from contrasting plant species in peatland ecosystems via 1) decay rates and 2) their ability to serve as a substrate for anaerobic methane production. This aim links ecosystem structure (plant species identity) to ecosystem function (litter decay, soil microbial activity). The approach was experimental placement of leaf litter from nine plant species that decayed in two bogs dominated by Sphagnum mosses, and two fens dominated by sedge grasses. The species were selected to give a large range of lignin (5 to 25%) and nitrogen (0.67 to 3.3%) concentrations. Measurements were made after decaying in the field just seven months, i.e., the initial stage of decay. These included the overall rate of mass loss, decay of several biochemical components in leaves (lignin, cellulose, hemicellulose, pectin, nitrogen), and colonization by methanogenic microorganisms.
Results/Conclusions
Leaf litter decay was faster in the bogs than in the fens. This reflects wetter soil conditions in fens that can reduce rates of aerobic respiration. Leaves from black alder (Alnus glutinosa), red maple (Acer rubrum), and sedge (Carex lacustris) had the fastest decay rates in the fens, whereas leaves from white pine (Pinus strobus), larch (Larix laricina) and the shrub leatherleaf (Chamaedaphne calyculata) had fast decay rates in the bogs. These patterns were not predicted by concentrations of lignin and / or nitrogen in leaves. Alder leaves were a remarkably good substrate for methane production. Alder is a symbiotic nitrogen fixer. However, leaves of another nitrogen-fixer bog myrtle (Myrica gale) did not support large rates of methane production, nor did common cattail (Typha latifolia) with a large concentration of nitrogen. Leaves from leatherleaf were a good methanogenic substrate when incubated in the bogs but less so in the fens. Also, leaves from white pine supported methanogenesis, as did leaves from pitch pine (Pinus rigida) and larch. Sedge and red maple supported slow rates of methane production. Deeper knowledge of leaf chemistry helped to explain the seemingly idiosyncratic patterns in decay rates and colonization by anaerobic methanogens.