The canopy structure and interception of photosynthetic photon flux density (PPFD) in a 10-year-old Kandelia candel (L.) Druce stand were investigated before and after artificial defoliation. Leaf and wood areas for different layers were measured through area-weight relationships of subsamples. PPFD was measured at specified heights before and after leaf clipping. The leaf area index (LAI) and wood area index (WAI) were 4.501 m 2 m Ϫ2 and 1.412 m 2 m Ϫ2 , respectively. There was a strong linear relationship between the cumulative wood area (C) and leaf area (F) densities from the top down to a given depth of the canopy, C ϭ aF (r 2 ϭ 0.950), with a proportional constant a of 0.096 Ϯ 0.008 (mean Ϯ SE). The PPFD relative to that above the canopy (relative PPFD; I R ) at a given depth of the canopy was assumed to be given by the equation I R ϭ e Ϫ(K C CϩK F F ) ϭ e ϪKF , where the apparent light extinction coefficient K (ϭ K F ϩ aK C , where K F and K C are respectively the light extinction coefficient of leaves and woody organs) was calculated to be 0.502 Ϯ 0.041 (mean Ϯ SE) m Ϫ2 m 2 before leaf clipping. After leaf clipping, I R C ϭ e ϪK C C is satisfied. As a result, the value of K C was estimated to be 0.785 Ϯ 0.046 (mean Ϯ SE) m Ϫ2 m 2 . The light extinction coefficient of leaves K F was calculated to be 0.427 m Ϫ2 m 2 using the indirect method, K F ϭ K Ϫ aK C , and 0.432 Ϯ 0.026 (mean Ϯ SE) m Ϫ2 m 2 using the direct method, I R /I R C ϭ e ϪK F F . Of the total PPFD intercepted by the canopy, the fraction K F /K due to leaves alone was estimated to be 85.0%-86.1% and the rest was contributed by woody organs.

Summary 1. Kleiman & Aarssen (2007) propose that the regression slope of the mean individual leaf mass across species vs. the number of leaves does not differ significantly from -1.0, based on logtransformed experimental data for tree shoots (i.e. isometric trade-off ). A quantitative model is set out here that explains the mechanism of isometric trade-off of leaf mass/number across species. 2. From Kleiman and Aarssen's result for the leaf mass/number trade-off in trees, the constancy of leaf biomass density per unit volume of shoot is derived theoretically. This constancy may scale up to the tree crown level, assuming proportionality of total shoot volume and crown volume, and also up to the canopy at stand level, based on the observed proportionality between crown depth and tree height. 3. On the basis of the constancy of leaf biomass density, the constancy of leaf biomass in a fully closed forest stand is analysed, since tree height tends to a limit as tree age increases due to hydraulic constraints. The resulting constancy of leaf biomass is consistent with previous reports for actual forest stands. 4. The allometric scaling theory of Enquist and colleagues suggests that metabolic rates of an entire organism scale as the 3/4 power of mass, so that scale-up is important: indeed, scaling up may be related to tree physiology and ecosystem carbon balance. The present scaling model from shoot to forest stand level is consistent with the work of Enquist and colleagues. The scaled-up result of leaf biomass constancy indicates that carbon uptake by forest stands may be almost constant if the mean leaf photosynthetic rate remains constant after closure of the forest canopy. 5. Synthesis. By analytically explaining the mechanism of the leaf mass/number trade-off at shoot level proposed by Kleiman and Aarssen, it is predicted that leaf biomass and carbon uptake are constant in fully closed forest stands, by scaling up the constancy of leaf biomass density from shoot to canopy level. The present analysis provides the theoretical basis for leaf biomass constancy in forest stands.

Nighttime respiration was measured at monthly intervals over one year on the aboveground parts of five sample trees in an 8-year-old hinoki cypress (Chamaecyparis obtusa (Sieb. et Zucc.) Endl.) stand, by an enclosed standing-tree method. The respiration rate rose rapidly from early spring to a maximum in June, and decreased abruptly in July and then gradually toward autumn and winter. The seasonal change in the respiration rate was synchronized with stem volume increment rather than with monthly mean air temperature. The respiration rate, r, of individual trees increased with increasing tree dimensions, such as stem volume, v(S), and stem girth at the base of the live crown, G(B). The dependence of respiration rate on tree size was successfully represented by a power function. The r - v(S) dependence was rather stronger than the r - G(B) (2) dependence, especially toward the end of the growing season (from July to September). The observed respiration rate was almost the same as the respiration rate corrected for the monthly mean air temperature. The annual respiration of individual trees was directly proportional to their phytomass or to its increment. Although the annual respiration of individual trees decreased proportionally to the square root of the leaf mass, it decreased abruptly in the range close to the smallest sample tree. Combining the monthly relationship between respiration rate and stem volume with the tree size distribution in the stand, the stand aboveground annual respiration was estimated to be 20.4 Mg CO(2) ha(-1) year(-1) (= 12.5 Mg dry mass ha(-1) year(-1)) for an aboveground biomass of 17.4 Mg ha(-1) with an annual increment of 6.51 Mg ha(-1) year(-1), i.e., the stand aboveground annual respiration amounted to the equivalent of 72% of the biomass or to almost twice the biomass increment.

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Carbon dioxide exchange in fruits of Cinnamomum camphora Sieb. was followed over a growing season from July to December 1992. Dark respiration was exponentially related to temperature, with a Q(10) value near 2. Light dependence of photosynthetic CO(2) refixation, i.e., the ratio of gross photosynthesis to dark respiration, was approximated by a hyperbolic function. Seasonal variation in maximum CO(2) refixation capacity ranged between 52 and 174%, reaching a maximum in early August. Daily photosynthetic CO(2) refixation ranged between 17 and 51% over the growth period. We evaluated seasonal variation in translocation rate to the fruit on the basis of the seasonal rates of gross photosynthesis, dark respiration and increase in fruit dry weight, and used the results to develop a simple carbon flow model of fruit development. Seasonal changes in translocation rate paralleled those in fruit growth rate, with two peaks during the periods before and after September. Seed formation took place in the period between the two peaks. The relationship between fruit growth rate and translocation rate was approximated by a linear function. The carbon flow model estimated that, over the reproductive period, the amount of assimilate translocated to each fruit was 377.2 mg dry weight, of which 58.5% was accounted for by weight growth and 41.5% was consumed by net respiration. Carbon dioxide refixation accounted for 22.9% of the carbon balance of the fruit.

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We investigated seasonal changes in dry mass and CO(2) exchange rate in fruit and leaves of the evergreen tree Cinnamomum camphora with the aim of quantitatively determining the translocation balance between the two organs. The fruit dry mass growth peaked in both August and October: the first increase was due to fruit pulp development and the second to seed development. Fruit respiration also increased with the rapid increase in fruit dry mass. Therefore, the carbohydrates required for fruit development showed two peaks during the reproductive period. Fruit photosynthesis was relatively high in early August, when fruit potentially re-fixed 75% of respired CO(2), indicating that fruit photosynthesis contributed 15-35% of the carbon requirement for fruit respiration. Current-year leaves completed their growth in June when fruit growth began. Current-year leaves translocated carbohydrates at a rate of approximately 10-25 mg dry weight (dw) leaf(-1) day(-1) into other organs throughout the entire fruit growth period. This rate of translocation from current-year leaves was much higher than the amount of carbohydrate required for reproduction (ca. 3 mg dw fruit(-1) day(-1)). Given the carbon balance between fruit and current-year leaves, carbohydrates for reproduction were produced within the current-year fruit-bearing shoots. C. camphora would be adaptive for steadily supplying enough amount of carbohydrate to the fruits, as there was little competition for carbohydrates between the two organs. As assimilates by leaves are used for processes such as reproduction and the formation of new shoots, photosynthesis by reproductive organs is considered to be important to compensate for reproductive cost.