The Impact of Land Use on Soil Properties and Structure of Ecosystem Carbon Stocks in the Middle Taiga Subzone of Karelia

The effects of land use changes on soil properties and ecosystem carbon stocks in the middle taiga subzone of Karelia on loamy Retisols of normal moistening are studied. The changes in soil profiles, main agrochemical and microbiological characteristics of the upper horizons, C-org and C-mic stocks in 1-m-thick soil layer, and the structure of carbon pools in individual plots are analyzed. The examined plots comprise cropland, hayfield, young (20-year-old) birch stand, middle-aged (65-year-old) spruce stand naturally regrown on former farmland, and mature (110-year-old) spruce stand as a control. The arable land has the soil density of 1.5 g/cm(3), pH 5.2, and a high content of nutrients. The C-org content in arable and hayfield soils falls in the range of 1.6-2.1% and N-tot is 0.2%. The forest soils have lower density (1.1-0.9 g/cm(3)), lower pH (4.0-3.2), and poorer agrochemical background, whereas the C-org content is increased to 2.2-4.6%. Characteristic of arable and mature forest soils is a decrease in the C-mic content to 50-60 mg C/kg soil. The C-mic content in hayfield, young forest stand, and middle-aged forest amounts to approximately 250 mg C/kg soil. The C-mic stock in 1-m thick soil layer reaches the maximum values of 88.9 g C/m(2) under the young forest stand; falls into the range of 52-61 g C/m(2) in the arable, hayfield, and middle-aged forest; and amounts to 23.6 g C/m(2) in the mature forest; as for the forest litter, the C-mic content is 14.5 g C/m(2). The total ecosystem carbon stock is the largest in the forest plots and smallest in hayfield. The C-org stock in the 1-m layer of cropland is 138 t C/ha, it decreases to 101-91 t C/ha in the young and middle-aged forest stands, and is minimal under the mature forest and hayfield (67-68 t C/ha).