Fine root distribution, seasonal pattern and production in four plantations compared with a natural forest in Subtropical China

Fine root (< 2 mm in diameter) distribution, seasonal pattern and net production were studied during 1999 - 2001 in 33 year-old plantations of two coniferous trees, Chinese fir ( Cunninghamia lanceolata, CF) and Fokienia hodginsii (FH) and two broadleaved trees, Ormosia xylocarpa (OX) and Castanopsis kawakamii (CK), and compared with that of an adjacent natural forest of Castanopsis kawakamii (NF, similar to 150 year old) in Sanming, Fujian, China. Fine root biomass and necromass were determined by soil coring at a bimonthly interval. Soil cores were divided into 10 depths: 0 similar to 10, 10 similar to 20, 20 similar to 30, 30 similar to 40, 40 similar to 50, 50 similar to 60, 60 similar to 70, 70 similar to 80, 80 similar to 90, and 90 similar to 100 cm. Litter bags ( 18 x 18 cm(2) size, 0.25 mm mesh) were used in determination the decay rates of fine roots (< 0.5 mm, 0.5 - 1 mm, and 1 - 2 mm). Mean annual fine-root production, mortality, decomposition and turnover rate were calculated by the compartment-flow method. Mean fine-root biomass ranged from 1.49 Mg ha(-1) in the CF to 4.94 Mg ha(-1) in the NF, and decreased in the following order: NF > CK > FH > OX > CF. There were significant seasonal changes of biomass and necromass in all stands ( P < 0.05), while no significant yearly fluctuations were detected ( P > 0.05). In all stands, an early spring ( March) peak of fine root biomass was found, and the minimum value occurred mainly in dry summer or cold winter. For the NF, 59.8% of fine root biomass was found in the top soil of 0 - 10 cm, a layer that maximum difference of depth distribution among all stands occurred, where fine root biomass of the NF was 2.37 times, 3.55 times, 8.12 times, and 7.12 times as much as those of the CK, FH, CF, and OX, respectively. Percentages of original mass lost during the first year of decomposition ranged from 43% to 56% for the FH to 68% to 80% for the NF. Mean annual root decomposition, mortality and production ranged from 8.47 Mg ha(-1) a(-1), 8.63 Mg ha(-1) a(-1) and 9.5 Mg ha(-1) a(-1) in the NF to 2.50, 2.49 and 2.51 Mg ha(-1) a(-1) in the CF, ranked as NF > CK > FH > OX > CF. The mean root turnover rate ranged from 1.48 a(-1) in the FH to 1.78 a(-1) in the NF.