The role of feathermosses in nitrogen cycling in lodgepole pine forests

The role of feathermoss in lodgepole pine forest ecosystems and the ability of feathermosses to assimilate and nitrogen (N) release in dissolved or gaseous form were studied. In a factorial experiment, mosses were either fertilized or allowed to dehydrate prior to a period of rewetting. N exchange between moss tissues and surrounding solutions was assessed continuously for 64 hours after wetting. Previous desiccation increased the amount of N leakage to the bathing solution. By 64 hours upon re-hydration feathermosses were capable to re-assimilate 2/3 of N released to the solution. In a second experiment, mosses were also either fertilized or dehydrated prior to treatment. Moss shoots were then rewetted and incubated directly in gas sampling vials. Desiccation increased production of N gases (N2 and N2O) and respiration rates of the moss layer; wet/dry cycles depleted carbohydrate content and decreased the total biomass of moss. This system of incubation provided superior accuracy compared to conventional chamber methods. Apparent loss of N from the feathermoss layer was verified by observed increase in natural levels of 15N from green feathermoss tissue, relative to decomposing brown tissue, and to the mineral soil, in soil columns from lodgepole pine stands. In a third experiment, moss was removed from a pine stand to directly determine the effect of feathermosses on pine N cycling and tree growth. Removal of the moss layer increased summer soil temperature and the duration of the frost-free period in the mineral soil, but as some of the winters during the study had below average snow cover, the soil rooting layer had temperatures below -13°C. There was little impact of moss removal on tree growth compared to the control treatment. In a fourth experiment, the effects of freeze-drying and air-drying provided new information on possible mechanisms of moss adaptation to desiccation. N was less susceptible to leakage upon rewetting, when the moss was subjected to gradual desiccation, compared to the freeze-dried moss. Most of the mineral N in the gradually desiccated moss was in NH4+ form, while in the freeze-dried moss, 40% of mineral N was in NO3- form.