Carbon dynamics associated with different land uses in north central Alberta.

摘要

Land use and land use change strongly influence the carbon (C) dynamics within ecosystems. This study quantified four aspects of land use and land use change effects: (1) ecosystem C stocks and distribution; (2) soil respiration; (3) soil C mineralization; and (4) net ecosystem productivity. Land use systems studied include agriculture (AG), 2-yr- and 9-yr-old hybrid poplar plantations (2HP and 9HP, respectively), grassland (GRA), and native forest stand (NAT). Ecosystem C stock in NAT (223 Mg C ha-1) was similar to 9HP (174 Mg C ha-1) and both were significantly greater than AG (122 Mg C ha-1), GRA (121 Mg C ha-1 ), and 2HP (110 Mg C ha-1). Cumulative soil C loss via soil respiration averaged over two growing seasons was in the order of: NAT (7.81+/-0.40 Mg C ha-1) > 9HP (5.51+/-0.31 Mg C ha-1) > GRA (5.23+/-0.30 Mg C ha-1 ) > AG (5.02+/-0.24 Mg C ha-1) > 2HP (4.28+/-0.20 Mg C ha-1). Depending on land use, seasonal heterotrophic and autotrophic respiration had respective contributions to soil respiration of up to 35 and 83%. Soil C mineralization of bulk soil across the land uses ranged between 2 to 5% of initial total organic C (Ci), with mineralization rates ranging from 0.06 to 0.12 microg C mg-1 C i d-1 and mean residence times ranging from 30 to 51 yrs. Across particle size fractions, soil C mineralization was in the order of: AG > HPs > GRA > NAT of which the coarse fractions, representing labile C, were the main source of mineralized C (79%). Mineralization increased when NAT was converted to AG; and decreased when AG was converted to HP or GRA. Net ecosystem productivity across land uses, expressed in terms of C, ranged between -2 (AG) and 11 Mg C ha-1 yr -1 (older HP). Conversion from AG to GRA increased net ecosystem productivity three-fold. When AG was converted to HP, the plantation was a C source in the first four years and became a C sink by year five. Results obtained from this study are relevant to modeling efforts designed at determining the impact of future climate change on a variety of land uses.