Growth and nutrition of black spruce seedlings in response to disruption of Pleurozium and Sphagnum moss carpets in boreal forested peatlands

Abstract

In boreal forested peatlands, we disturbed Sphagnum spp. and Pleurozium schreberi carpets to see how disturbance influenced substrate physico-chemistry, and growth and foliar nutrition of planted Picea mariana seedlings. Carpets were hand disturbed using gardening tools to a depth of approximately 25 cm. Carpet disturbance was aimed at disrupting only the organic layer and did not result in the mixing of organic matter with mineral soil. Disturbed carpets, whether P. schreberi or Sphagnum spp., were warmer than undisturbed carpets and had a lower cover of ericaceous shrubs. Pleurozium schreberi carpets had a higher decomposition index than Sphagnum spp. carpets, whereas disturbance had no effect on this variable. Pleurozium schreberi had higher Ntot and dissolved organic N concentrations (DON) than Sphagnum spp., whereas disturbance increased NH 4 + availability in both substrates. Moss disruption increased seedling growth rates as well as their foliar N and P concentrations in both substrates and these variables remained higher in P. schreberi than in Sphagnum spp. within a given treatment. Seedling growth was positively correlated to substrate Ntot, NH 4 + and DON concentrations, and to foliar N and P concentrations, and negatively to substrate C/N and ericaceous shrub cover. Disruption of the moss carpets without mineral soil mixing improved black spruce seedling growth and nutrition in both moss types but the superiority of P. schreberi compared to Sphagnum spp. as a growing substrate remained present.