Photosynthetic traits of two-year-old Japanese larch seedlings (Larix kaempferi Carr.) grown at elevated CO2 concentrations were studied in relation to structural changes in the needles. Seedlings were grown at two CO2 concentrations, 360 (AC) and 720 (EC) μmol mol-1 at high and low nutrient supply rates, high N (HN) and low N (LN). The photosynthetic capacity fell significantly in EC+LN, but increased significantly in EC+HN. Since the mesophyll surface area exposed to intercellular space per unit leaf area (Ames/A) is correlated with the photosynthetic rate, we measured Ames/A for larch needles growing in EC. Changes of Ames/A in both EC+HN and EC+LN were very similar to the changes in photosynthetic capacity. This suggests that the changes of Ames/A in EC probably caused the changes in the photosynthetic capacity. The changes of Ames/A in EC were attributed to changes in the mesophyll cell size and mesophyll cell number. The photosynthetic capacity in EC can be explained by taking morphological and structural adaptations into account as well as biochemical factors. and N. Eguchi ... [et al.].
The effects of four manganese (Mn) concentrations (1, 10, 50, and 100 g m-3 = Mn1, Mn10, Mn50, Mn100) in solution culture on growth variables were studied for seedlings of five deciduous broad-leaved trees with different successional characteristics and shoot development patterns in northern Japan. The five species were: Betula ermanii, Betula platyphylla var. japonica, and Alnus hirsuta (early-successional species with continuous leaf development), Ulmus davidiana var. japonica (mid-successional species with flush and continuous leaf development), and Acer mono (late-successional species with a flush type leaf development). In plants grown in the Mn environment for about 45 d, relative growth rate (RGR) decreased with increasing Mn supply. Between the 1 and 100 g(Mn) m-3, RGR decreased by 20 % for B. ermanii and B. platyphylla, by 40 % for A. hirsuta and A. mono, and by 80 % for U. davidiana. Specific leaf area (SLA) and leaf mass ratio (LMR) of all species were little affected by high Mn supply. In U. davidiana, however, there was a 67 % decrease in LMR in Mn100 plants. Leaf area ratio (LAR) was higher in early-successional species than in mid- and late-successional ones but differed little among Mn treatments within species, except for U. davidiana where LAR declined substantially with increased Mn supply. While LAR, which represents the relative size of assimilatory apparatus, was little affected, net photosynthetic rate (PN) saturated with radiant energy decreased with increasing Mn supply in all species. Thus PN was adversely affected by high accumulation of Mn in leaves, which resulted in an overall reduction in biomass production. However, the proportional allocation of photosynthates to the assimilatory apparatus was not affected by different Mn toxicity in hardwood tree seedlings. and M. Kitao, T. T. Lei, T. Koike.
We investigated the responses of photon-saturated photosynthesis rate (Psat) and its simultaneous acclimation of anatomy and nitrogen use patterns of current needles of Korean pine (Pinus koraiensis) seedlings grown under factorial combinations of two nitrogen levels and irradiances. Although N supply resulted in a significant increase of N content in needles under both irradiances, the increase of P sat tended to be suppressed only in shade (S). The significant increase of P sat in full sunlight (O) was associated with the increase of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and chlorophyll (Chl) contents. In contrast, small increase of Chl content and no increase of RuBPCO content were found in S (90 % cut of full irradiance), which would result in a small increase of Psat. This result suggests that extra N is stocked in needles under shade for the growth in next season. With N supply, a significant decrease of specific leaf area (SLA) was detected only in O. This decrease of SLA was due to the increase of density of needle. Furthermore, the increase of needle density was not due to the increased number and size of mesophyll cells, but the increased density of each mesophyll cell. Therefore, although SLA changed in O, the change did not involve anatomical adaptation to use increased N effectively, at least observable by light microscopy. Hence, even though the SLA would change, N deposition will improve the photosynthetic capacity of Korean pine seedlings, not through the development of needle anatomy but through improvement of the allocation of N in both irradiances. and K. Makoto, T. Koike.
To find the effects of CO2 enrichment on plant development and photosynthetic capacity of nodulated (line A62-1) and non-nodulated (line A62-2) isogenic lines of soybean (Glycine max Merr.), we examined the interactions among two CO2 treatments (36±3 Pa = AC and 70±5 Pa = EC), and two nitrogen concentrations [0 g(N) m-2(land area) = 0N; 30 g(N) m-2(land area) = 30N]. Nodules were found in both CO2 treatments in 0N of A62-1 where the number and dry mass of nodules increased from AC to EC. While the allocation of dry mass to root and shoot and the amount of N in each organ did not differ between the growth CO2 concentrations, there was larger N allocation to roots in 0N than in 30N for A62-2. The CO2-dependence of net photosynthetic rate
(PN) for A62-1 was unaffected by both CO2 and N treatments. In contrast, the CO2-dependence of PN was lower in 0N than in 30N for A62-2, but it was independent of CO2 treatment. PN per unit N content was unaffected by CO2 concentrations. The leaf area of both soybean lines grown in 30N increased in EC. But in 0N, only the nodulated A62-1 showed an increase in leaf area in EC. Nitrogen use efficiency of plants, NUE [(total dry mass of the plant)/(amount of N accumulated in the plant)] in 30N was unaffected by CO2 treatments. In 0N, NUE in EC was lower than in AC in A62-1, and was higher than that at AC in A62-2. Hence, the larger amount and/or rate of N fixation with the increase of the sink-size of symbiotic microorganisms supplied adequate N to the plant under EC. In EC, N deficiency caused the down-regulation of the soybean plant. and T. Nakamura ... [et al.].