Ecosystem carbon stocks and distribution under different land-uses in north central Alberta, Canada

Land-use and land cover strongly influence carbon (C) storage and distribution within ecosystems. We studied the effects of land-use on: (i) above- and belowground biomass C, (ii) soil organic C (SOC) in bulk soil, coarse- (250-2000 mu m), medium-(53-250 mu m) and fine-size fractions (<53 mu m), and (iii) C-13 and N-15 abundance in plant litter, bulk soil, coarse-, and medium- and fine-size fractions in the 0-50 cm soil layer in Linaria AB, Canada between May and October of 2006. Five adjacent land-uses were sampled: (i) agriculture since 1930s, (ii) 2-year-old hybrid poplar (Populus deltoides x Populus x petrowskyana var. Walker) plantation, (iii) 9-year-old Walker hybrid poplar plantation, (iv) grassland since 1997, and (v) an 80-year-old native aspen (Populus tremuloides Michx.) stand. Total ecosystem C stock in the native aspen stand (223 Mg C ha(-1)) was similar to that of the 9-year-old hybrid poplar plantation (174 Mg C ha-1) but was significantly greater than in the agriculture (132 Mg C ha(-1)), 2-year-old hybrid poplar plantation (110 Mg C ha-1), and grassland (121 Mg C ha(-1)). Differences in ecosystem C stocks between the landuses were primarily the result of different plant biomass as SOC in the 0-50 cm soil layer was unaffected by land-use change. The general trend for C stocks in soil particle-size fractions decreased in the order of: fine > medium > coarse for all land-uses, except in the native aspen stand where C was uniformly distributed among soil particle-size fractions. The C stock in the coarse-size fraction was most affected by land-use change whilst the fine fractions the least. Enrichment of the natural abundances of C-13 and N-15 across the land-uses since time of disturbance, i.e., from agriculture to 2- and then 9-year-old hybrid poplar plantations or to grassland, suggests shifts from more labile forms of C to more humified forms of C following those land-use changes. (C) 2009 Elsevier B.V. All rights reserved.