-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 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 wherelitterfall / nutrient return / litter decomposition / reafforestation / natural forest / Cunninghamia lanceolata / Fokienia hodginsii / Ormosia xylocarpa / Castanopsis kawakamii Résumé -Chute de feuilles, retour de nutriments et décomposition des feuilles de la litière dans quatre plantations en comparaison avec une forêt naturelle en Chine subtropicale. La quantité et la dynamique de chute de litière, le retour des nutriments, la composition chimique initiale des feuilles de la litière et la dynamique de N, Pet K associée à la décomposition de la litière ont été étudiés dans 2 plantations de conifères (Cunninghamia lanceolata, CF and Fokienia hodginsii, FH) âgées de 33 ans et 2 peuplements feuillus (Ormosia xylocarpa, OX et Castanopsis kawakamii, CK), comparativement à une forêt naturelle adjacente de Castanopsis kawakamii, NF, âgée d'environ 150 ans à Sanming, Fujian, Chine. Sur 3 années d'observations, la moyenne annuelle de chute de litière a été de 5,47 Mg·ha -1 pour CF, 7,29 Mg·ha -1 pour FH, 5,69 Mg·h -1 pour OX, 9,54 Mg·hg -1 pour CK et 11,01 Mg·h...

Changes in the total phenolics, condensed tannins (CT), protein-precipitable phenolics content and protein precipitation capacity were determined on a series of mangrove leaves from two true viviparous mangrove species (Kandelia candel and Bruguiera gymnorrhiza) at various stages of development and decomposition in the Jiulong River Estuary, Fujian, China. Similar measurements were also done for the propagules at different developmental stages. The results showed that the total phenolics, extractable condensed tannins, total condensed tannins, proteinprecipitable phenolics content and protein precipitation capacity in young leaves were higher than those in mature and senescent leaves. Tannin dynamics during leaf decomposition varied with species, and the rapid loss of phenolics observed during decomposition can be ascribed to leaching and degradation. Protein-bound CT and fibre-bound CT tended to increase with leaf decomposition, with CT binding more strongly to protein than to fibre. Protein-bound CT was higher than fibre-bound CT with the exception of mature leaves. Total phenolics, extractable CT and proteinprecipitable phenolics contents in flower tissues were relatively lower than those in hypocotyls at different developmental stages. Protein precipitation capacity fluctuated with the development of propagules. Increases in nitrogen in decaying litter, and declines in contents of total phenolics and total condensed tannins of detritus support the general conclusion that decomposing mangrove detritus can be a more palatable heterotrophic substrate than living leaves.

-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, ~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 ~ 10, 10 ~ 20, 20 ~ 30, 30 ~ 40, 40 ~ 50, 50 ~ 60, 60 ~ 70, 70 ~ 80, 80 ~ 90, and 90 ~ 100 cm. Litter bags (18 × 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. On a utilisé des sacs à litière (18 × 18 cm 2 , maille de 0,25 mm) pour déterminer le taux de décomposition des radicelles (< 0,5 mm, 0,5-1 mm, 1-2 mm). Les taux de production moyenne annuelle, de mortalité, de décomposition et de turnover des radicelles ont été calculés par la méthode de « compartment flow ». La biomasse moyenne de radicelles va de 1,49 Mg/ha dans le CF à 4,94 Mg/ha pour le NF ; elle décroît dans l'ordre suivant : NF > CK > FH > OX > CF. On a enregistré des différences significatives de biomasse et nécromasse, selon les saisons dans tous les peuplements (P < 0,05), tandis qu'aucune fluctuation n'a pu être mise en évidence entre années (P > 0,05). Pour tous les peuplements, on enregistre un pic de biomasse de radicelles au début du printemps (mars), les valeurs minimum intervenant au cours d'étés secs ou d'hivers froids. Pour le NF, 59,8 % de la biomasse de radicelles se situe dans la zone superficielle ...

No abstract

No abstract