RESPONSE OF ABOVEGROUND NET PRIMARY PLANT-PRODUCTION TO NITROGEN AND PHOSPHORUS FERTILIZATION IN PEATLANDS IN SOUTHERN BOREAL ALBERTA, CANADA

In order to determine whether nitrogen (N) or phosphorus (P) limits ab oveground plant growth in peatlands in Alberta, we fertilized one bog, two fens, and two marshes with N and P at a ratio of 7:1 (Redfield ra tio of these two elemental nutrients in aquatic plants) as well as wit h water without either fertilizer in 1994. The response of aboveground plant production to N or P was species-specific and varied among the sites. In the bog, Smilacina trifolia, a herb, showed significant incr eases in net primary production (NPP) after fertilization with N plus water and the addition of water, while Andromeda polifolia only showed significant increases in NPP after fertilization with N plus water. L edum groenlandicum, an ericaceous shrub, showed significant decreases in NPP after additions of N plus water, P plus water, and water, while Oxycoccus quadripetalus, another ericaceous shrub, also showed signif icant decreases of NPP after additions of N plus water and water. Spha gnum fuscum (moss) NPP increased significantly after the additions of water and decreased significantly after the additions of N plus water and P plus water. In the fens and marshes, only Carer spp. in the lacu strine sedge fen showed a significant increase in NPP after the additi on of N. Vascular NPP (shrubs and herbs combined) did not increase sig nificantly in any of the five peatlands. Total NPP (moss, herb, and sh rub strata combined) increased significantly only in the bog after the addition of water due to the dominance of the moss stratum in that si te. In the bog, moss growth was limited by water, and herb and shrub g rowth responses to N and P fertilization were species-specific. Neithe r N nor P limited aboveground plant production in the fens and marshes .