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

Chia sẻ: Nguyễn Minh Thắng | Ngày: | Loại File: PDF | Số trang:3

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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: A model of light interception and carbon balance for sweet chestnut coppice (Castanea sativa Mill.)...

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A model of light interception and carbon balance for a sweet chestnut coppice (Castanea sativa Mill.) L. Mordacq B. Saugier Laboratoire d’Ecologie V6g6tale (CNRS URA121), Bit 362, Université Paris-Sud, Orsay 91405 Cedex, France air temperature within 4°C with respect to the Introduction 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 the synthesis, young tree photosynthesis, heterogeneous structure of the canopy, which is wood 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 no designed a model to predict photosynthe- the end of the first foliage of different trees until year. The leaves in the model were distributed sis of heterogeneous canopies and wood homogeneously within ellipsoids or fractions of respiration. The output of the model to- ellipsoids around each stump. The dimensions gether with measurements of aerial of the ellipsoids were measured in situ and the growth enabled calculation of the amount trees were distributed randomly on the soil sur- face, except that there could be no intersection of 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 (Norman Leaf photosynthesis has been measured in situ on attached leaves using a laboratory- made assimilation chamber with control of leaf temperature by Peltier elements. The chamber was working as an open system and the leaf temperature was fixed at 24°C. Measurements were made throughout the growing season. Tree photosynthesis was measured in situ on 1 yr old chestnut tree using a large assimila- a tion chamber (0.9 m x 0.9 m x 1.8 m high) built in 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 in
and Welles, 1983). Diffuse light was treated as tion level was 600 pE. the maxi- ; 1 S 2 - M direct light and integrated over the whole sky. photosynthesis level was 13 pmol mum Thus the model enabled calculation of sha- -s-B -m- 2 C0 dowing between trees. As the trees grew, the ellipsoids 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 the Photosynthesis was calculated on an hourly tree) compared with the outputs of the basis. 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 pmol Results . about half of the maximum , 1 s- ’ 2 m- z’ CO leaf photosynthesis. Agreement between measurements and model outputs is good. However, at low light levels, the model underestimated photosynthesis for overcast sky conditions and overestimated it for clear sky conditions. Conclusion In its present iform, the model does not account for assimilate partitioning. We used it to derive a carbon balance of the
carbon allocated to roots is similar to that stand, computed as the difference be- stored in shoots. tween net assimilation (predicted) and total (growth and maintenance) shoot respiration (measured and fitted to tem- perature). The allocation of carbon to References roots was tentatively computed as the dif- ference between the net amount of carbon de Wit C.T. (1965) Photosynthesis of leaf cano- entering the plant and the measured pies. Versl. Landbouwkd. Onderz. (Agr. Res. amount of carbon stored by the shoots Rep.) 64, 57-67 during growth. Fig. 4 shows these various Dubroca E. & Saugier B. (1988) Effet de la components. Roots apparently act as a coupe sur 1’6volution saisonnibre des r6serves of carbon from early spring until glucidiques dans un taillis de ch taigniers. g source Bull. Soc. Bot Fr. 135, Actual. Bot. 1, 55-64 mid-July, which is confirmed by measure- Mordacq L. & Saugier B. (1989) A simple field a strong decrease in root ments showing method for measuring the gas exchange of starch concentration during that time small trees. Funct. EcoL in press (Dubroca and Saugier, 1988). Later on Norman J.M. & Welles J.M. (1983) Radiative they become a strong sink and, at the end transfer in an array of canopies. Agron. J. 77, of the season, the accumulated amount of 481-488

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