Decomposition of fine roots (<2 mm in diameter, viz. <0.5mm, 0.5-1.0mm, 1.0-2.0mm) was studied by means of litter bag in a mixed forest of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) and Tsoong's tree (Tsoongiodendron odorum Chun) in Sanming, Fujian, China. In a 540 d period of decay, fine roots in all litter bags decomposed in a three-phase manner: (a) for the Chinese fir, an initial, relatively low rate of decay up to 90 d followed by a period of rapid weight loss until 270 d, and then by a phase of slow decay rate; (b) for the Tsoong's tree, a rapid loss period between 0-60 d followed by a relatively rapid loss period between 60-360 d, and then a slow loss period between 360-540 d occurred. The mass loss after 1 yr of decomposition ranged from 58.5% to 63.3% for the Chinese fir and 68.8% to 78.2% for the Tsoong's tree. Fine roots with a larger diameter had a lower rate of mass loss. Consistent increase in lignin concentration and decrease in absolute amount of phosphorus (P) were found for fine roots of the two tree species during decomposition. The absolute amounts of nitrogen (N) increased a little initially in the fine roots of the Chinese fir during a short duration. In contrast, the fine roots of Tsoong's tree were releasing N from the outset. The chemical composition controlled decomposition rate and it was found a change of TNC (total nonstructural carbohydrates)-regulating in the initial decomposition phase to lignin- or N-regulating in the second phase, and P- or lignin-regulating in the last phase.

The amount and pattern of litterfall, its nutrient return, initial chemistry of leaf litter, and dynamics of N, P and K associated with leaf-litter decomposition were studied 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,～150 year old) in Sanming, Fujian, China. Mean annual total litterfall over 3 years of observations was 5.47 Mg•ha-1 in the CF, 7.29 Mg•ha-1 in the FH, 5.69 Mg•ha-1 in the OX, 9.54 Mg•ha-1 in the CK and 11.01 Mg•ha-1 in the NF respectively; of this litterfall, leaf contribution ranged from 58% to 72%. Litterfall in the OX, CK, and NF showed an unimodal distribution pattern, while for the CF and FH, the litterfall pattern was multi-peak. The highest annual Ca and Mg returns were noticed in the FH and in the CK, respectively. The amounts of N, P, and K which potentially returned to the soil were the highest in the NF. The loss of dry matter in leaf litter exhibited a negative exponential pattern during the 750-day decomposition. Using the model xt=A+Be-kt, the annual dry matter decay constants (k) ranged from 1.157 in CF to 4.619 in OX. Initial lignin concentration and lignin/N ratios showed significantly negative correlations with k (r=-0.916, P=0.011; r=-0.473, P=0.041), whereas initial N concentration showed low positive correlations (r=0.225, P=0.038). Using the model xt=A+Be-kt, the decay constant of N (kN) ranged from 0.769 in CF to 4.978 in OX; the decay constant of P (kP) ranged from 1.967 in the OX to 4.664 in the NF; and the decay constant of K (kK) seemed very similar among these forests (5.250-5.992). The decay constants of nutrients during leaf-litter decomposition can be arranged in the sequence of kK>kP>kN, except for leaf litter of OX where kK>kN>kP.

ed in Yizhou work area of Yizhou state Forestry Centre in Fujian Province, China, were examined following slash burning to compare nutrient capital and topsoil properties with preburn levels. After fire, nutrient (N, P and K) removal from burning residues was estimated at 302.5 kg ha-1 in the CF and 644.8 kg ha-1 in the EB. Fire reduced the topsoil capitals of total N and P by ～20% and ～10%, respectively in both forests. While K capital was increased in the topsoils of both forests following fire. Total site nutrient loss through surface erosion was 28.4kg (N) ha-1, 8.4kg (P) ha-1 and 328.7kg (K) ha-1 in the CF. In the EB, the losses of total N, P and K were 58.5, 10.5 and 396.3kg ha-1, respectively. Improvement of soil structure and increase in mineralization of nutrients associated with increased microbe number and enzyme activities and elevated soil respiration occurred 5 days after fire. However, organic matter and available nutrient contents and most of other soil parameters declined one year after fire on the burned CF and EB topsoils. These results suggest that short-term site productivity can be stimulated immediately, but reduced subsequently by soil and water losses, especially in South China, where high-intensity precipitation, steep slopes and fragile soil factor can be expected. Therefore, the silvicultural measurements should be developed in plantation management.