Báo cáo lâm nghiệp: A model of light interception and carbon balance for sweet chestnut coppice (Castanea sativa Mill.)

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Báo cáo lâm nghiệp: "A model of light interception and carbon balance for sweet chestnut coppice (Castanea sativa Mill.)"A model of light interception and carbon balance for asweet chestnut coppice (Castanea sativa Mill.)L. Mordacq B. SaugierLaboratoire d’Ecologie V6g6tale (CNRS URA121), Bit 362, Université Paris-Sud, Orsay 91405Cedex, France air temperature within 4°C with respect to theIntroduction outside (Mordacq and Saugier, 1989). Measure- ments were performed at the end of the grow- ing season during August and September.Data have been collected on leaf photo- The assimilation model took into account thesynthesis, young tree photosynthesis, heterogeneous structure of the canopy, which iswood respiration and aerial growth in a necessary during the first years after the cut.sweet chestnut (Castanea sativa Mill.) Each tree was first considered as being iso-coppice for several years after a cut. We lated; there intersection between the was nodesigned a model to predict photosynthe- the end of the first foliage of different trees until year. The leaves in the model were distributedsis of heterogeneous canopies and wood homogeneously within ellipsoids or fractions ofrespiration. The output of the model to- ellipsoids around each stump. The dimensionsgether with measurements of aerial of the ellipsoids were measured in situ and thegrowth enabled calculation of the amount trees were distributed randomly on the soil sur- face, except that there could be no intersectionof carbon allocated to roots. between the ellipsoids at the end of the first year. The light penetration was calculated at randomly distributed points P by calculating the extinction coefficient from the leaf angle distri-Materials and Methods bution (de Wit, 1965), and the pathlength (Fig. 1) of light rays R through the ellipsoids (NormanLeaf photosynthesis has been measured insitu on attached leaves using a laboratory-made assimilation chamber with control of leaftemperature by Peltier elements. The chamberwas working as an open system and the leaftemperature was fixed at 24°C. Measurementswere made throughout the growing season. Tree photosynthesis was measured in situ on 1 yr old chestnut tree using a large assimila-ation chamber (0.9 m x 0.9 m x 1.8 m high) builtin the laboratory and working as an open sys-tem. A high flow of air through the cham-ber (maximum 0.08 m3!s-!) kept the increase inand Welles, 1983). Diffuse light was treated as tion level was 600 pE. the maxi- ; 1 S 2 - Mdirect light and integrated over the whole sky. photosynthesis level was 13 pmol mumThus the model enabled calculation of sha- -s-B -m- 2 C0dowing between trees. As the trees grew, theellipsoids grew to the point where the soil was Fig. 3 shows the tree photosyn-completely covered by the canopy (Fig. 1 ). thesis-light curve (by unit leaf area of thePhotosynthesis was calculated on an hourly tree) compared with the outputs of thebasis. model for a single tree and for two light conditions. The light saturation was at 600 pE-m-- and the maximum -s-1 2 tree photosynthesis level was 6 pmolResults . about half of the maximum , 1 s- ’ 2 ...