The calculated maximum net photosynthetic rate (PN) at saturation irradiance (I m) of 1 314.13 µmol m-2 s-1 was 25.49 µmol(CO2) m-2 s-1, and intrinsic quantum yield at zero irradiance was 0.103. The results fitted by nonrectangular hyperbolic model, rectangular hyperbolic method, binomial regression method, and the new model were compared. The maximum PN values calculated by nonrectangular hyperbolic model and rectangular hyperbolic model were higher than the measured values, and the I m calculated by nonrectangular hyperbolic model and rectangular hyperbolic model were less than measured values. Results fitted by new model showed that the response curve of PN to I was nonlinear at low I for Oryza sativa, PN increased nonlinearly with I below saturation value. Above this value, PN decreased nonlinearly with I.
The objective of the present investigation was to examine the extent of variations in single leaf net photosynthetic rate (PN) and its relative dependence on stomatal conductance (gs) and the mesophyll capacity to fix carbon in 12 clones of the natural rubber plant. There were significant variations in PN measured at low and saturating photon flux density (PFD); the extent of variation was larger at low than at saturating PFD. The compensation irradiance (CI) and apparent quantum yield of CO2 assimilation (φc) calculated from the PN/PFD response curves showed significant variations among the clones. PN at low irradiance was positively correlated with φc. Thus a clone with large PN at low irradiance, high φc, and low CI may tolerate shade better and thus produce a high tree stand per hectare. A strong positive correlation existed between PN saturated with radiant energy (Psat) and carboxylation efficiency (CE) estimated from the response curves of PN on intercellular CO2 concentration (Ci), but gs showed a poor correlation with Psat High CO2 compensation concentration (Γ) led to low CE in Hevea clones. A clone with large Psat, high CE, low gs, and low Γ is the one in which photosynthesis is more dependent on the mesophyll factors than stomata. Such a clone may produce relatively high biomass and maintain high water use efficiency. and K. N. Nataraja, J. Jacob.
Net photosynthetic rate (PN) of leaves grown under free-air CO2 enriched condition (FACE, about 200 µmol mol-1 above ambient air) was significantly lower than PN of leaves grown at ambient CO2 concentration (AC) when measured at CO2 concentration of 580 µmol mol-1. This difference was found in rice plants grown at normal nitrogen supply (25 g m-2; NN-plants) but not in plants grown at low nitrogen supply (15 g m-2; LN-plants). Namely, photosynthetic acclimation to FACE was observed in NN-plants but not in LN-plants. Different from the above results measured in a period of continuous sunny days, such photosynthetic acclimation occurred in NN-plants, however, it was also observed in LN-plants when PN was measured before noon of the first sunny day after rain. Hence strong competition for the assimilatory power between nitrogen (N) and carbon (C) assimilations induced by an excessive N supply may lead to the photosynthetic acclimation to FACE in NN-plants. The hypothesis is supported by the following facts: FACE induced significant decrease in both apparent photosynthetic quantum yield (Φc) and ribulose-1,5-bisphosphate (RuBP) content in NN-plants but not in LN-plants. and Z.-H. Yong ... [et al.].
We found differences between true leaves (TL) and phyllodes (Ph) during ontogeny of Acacia mangium plants as reflected in chlorophyll (Chl) and carotenoid contents, gas exchange, Chl fluorescence, and growth. The production of TL enhanced the relative growth rate of the A. mangium seedlings, allowing the plants to accumulate enough dry biomass for later growth, while the production of thicker Ph in the later growth stage of A. mangium could help plants to cope with higher irradiance in their natural growth conditions. and H. Yu, J.-T. Li.
To assess photosynthesis and yield components' response of field-grown wheat to increasing ozone (O3) concentration (based on diurnal pattern of ambient O3) in China, winter wheat (Triticum aestivum L.) cv. Jia 403 was planted in open top chambers and exposed to three different O3 concentrations: O3-free air (CF), ambient air (NF), and O3-free air with additional O3 (CF+O3). Diurnal changes of gas exchange and net photosynthetic rate (PN) in response to photosynthetic photon flux density (PPFD) of flag leaves were measured at the filling grain stage, and yield components were investigated at harvest. High O3 concentration altered diurnal course of gas exchange [PN, stomatal conductance (gs), and intercellular CO2 concentration (Ci)] and decreased significantly their values except for Ci. Apparent quantum yield (AQY), compensation irradiance (CI), and saturation irradiance (SI) were significantly decreased, suggesting photosynthetic capacity was also altered, characterized as reduced photon-saturated photosynthetic rate (PNmax). The limit of photosynthetic activity was probably dominated by non-stomatal factors in combination with stomatal closure. The significant reduction in yield was observed in CF+O3 treatment as a result of a marked decrease in the ear length and the number of grains per ear, and a significant increase in the number of infertile florets per ear. Even though similar responses were also observed in plants exposed to ambient O3 concentration, no statistical difference was observed at current ambient O3 concentration in China. and Z.-Z. Feng ... [et al.].
Functional differentiation of assimilation activity of sun versus shade foliage was analysed in a Norway spruce monoculture stand (age 15 years). The investigated stand density (leaf area index 8.6) and crown structure led to variation in the photosynthetically active photon flux density (PPFD) within the crowns of the sampled trees. At the saturating PPFD, the maximum rate of CO2 uptake (PNmax) of exposed shoots (E-shoots) was 1.7 times that of the shaded shoots (S-shoots). The apparent quantum yield (α) of E-shoots was 0.9 times that of the S-shoots. A lower ability to use excess energy at high PPFD in photosynthesis was observed in the S-layer. The CO2- and PPFD-saturated rate of CO2 uptake (PNsat) of the E-shoots was 1.12 times and the carboxylation efficiency (τ) 1.6 times that of the S-shoots. The CO2-saturated rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) carboxylation (VCmax) and of actual electron transport (Jamax) in the S-needles amounted to 89 and 95 % of VCmax and Jamax in the E-needles. Thus, in addition to the irradiation conditions and thus limitation by low Ja, the important limitation of photosynthesis in shade needles is due to carboxylation. This limitation of photosynthesis is accompanied by lower stomatal conductance. and M. Šprtová, M. V. Marek.