Response of aboveground net primary plant production to nitrogen and phosphorus fertilization in peatlands in southern boreal Alberta, Canada

Abstract

In order to determine whether nitrogen (N) or phosphorus (P) limits aboveground 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 ratio of these two elemental nutrients in aquatic plants) as well as with 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 increases in net primary production (NPP) after fertilization with N plus water and the addition of water, whileAndromeda polifolia only showed significant increases in NPP after fertilization with N plus water.Ledum groenlandicum, an ericaceous shrub, showed significant decreases in NPP after additions of N plus water, P plus water, and water, whileOxycoccus quadripetalus, another ericaceous shrub, also showed significant decreases of NPP after additions of N plus water and water.Sphagnum 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, onlyCarex spp. in the lacustrine sedge fen showed a significant increase in NPP after the addition of N. Vascular NPP (shrubs and herbs combined) did not increase significantly in any of the five peatlands. Total NPP (moss, herb, and shrub strata combined) increased significantly only in the bog after the addition of water due to the dominance of the moss stratum in that site. In the bog, moss growth was limited by water, and herb and shrub growth responses to N and P fertilization were species-specific. Neither N nor P limited aboveground plant production in the fens and marshes.