Litterfall, nutrient return, and leaf-litter decomposition in four plantations compared with a natural forest in subtropical China

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, similar to150 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 x(t) = 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 x(t) = A + Be-kt, the decay constant of N (k(N)) ranged from 0.769 in CF to 4.978 in OX; the decay constant of P (k(p)) ranged from 1.967 in the OX to 4.664 in the NF; and the decay constant of K (k(K)) 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 k(K) > k(P) > k(N), except for leaf litter of OX where k(K) > k(N) > k(P).