In order to study the responses of dominant species to different land uses in the semiarid temperate grassland of Inner Mongolia, we tested the physiological responses of Stipa grandis, Leymus chinensis, and Artemisia frigida to mowing, grazing exclusion, and grazing land uses at the leaf and ecosystem levels. The grazing-exclusion and mowing sites released CO2, but the grazing site was a net carbon sink. L. chinensis and S. grandis contributed more to the ecosystem CO2 exchange than A. frigida. At the grazing-exclusion and mowing sites, Leymus chinensis and Stipa grandis both exhibited a higher light-saturation point and higher maximum photosynthetic rate than that at the grazing site, which increased photosynthesis and growth compared to those at the grazing site. In contrast, A. frigida possessed a higher nitrogen content than the other species, and more of the light energy used for photosynthesis, particularly at the grazing site., M. Liu, J. R. Gong, Y. Pan, Q. P. Luo, Z. W. Zhai, L. L. Yang, S. Xu., and Obsahuje bibliografii
The response of effective quantum yield of photosystem 2 (ΔF/Fm') to temperature was investigated under field conditions (1 950 m a.s.l.) in three alpine plant species with contrasting leaf temperature climates. The in situ temperature response did not follow an optimum curve but under saturating irradiances [PPFD >800 µìmol(photon) m-2s-1] highest ΔF/Fm' occurred at leaf temperatures below 10°C. This was comparable to the temperature response of antarctic vascular plants. Leaf temperatures between 0 and 15°C were the most frequently (41 to 56%) experienced by the investigated species. At these temperatures, ΔF/Fm' was highest in all species (data from all irradiation classes included) but the species differed in the temperature at which ΔF/Fm' dropped below 50% (Soldanella pusilla >20°C, Loiseleuria procumbens >25°C, and Saxifraga paniculata >40°C). The in situ response of ΔF/Fm' showed significantly higher ΔF/Fm' values at saturating PPFD for the species growing in full sunlight (S. paniculata and L. procumbens) than for S. pusilla growing under more moderate PPFD. The effect of increasing PPFD on ΔF/Fm', for a given leaf temperature, was most pronounced in S. pusilla. Despite the broad diurnal leaf temperature amplitude of alpine environments, only in S. paniculata did saturating PPFD occur over a broad range of leaf temperatures (43 K). In the other two species it was half of that (around 20 K). This indicates that the setting of environmental scenarios (leaf temperature×PPFD) in laboratory experiments often likely exceeds the actual environmental demand in the field. and V. Braun, G. Neuner.
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.].
Intact cells of Synechococcus elongatus were treated with different concentrations (0.1 and 1.0 mM = Cd0.1, Cd1.0) of CdCl2 for 24 h. Cd0.1 treatment stimulated growth of the cell culture and chlorophyll (Chl) a concentration in the culture. Cd1.0 inhibited both the above mentioned parameters. The oxygen evolving activity of intact cells (H2O → BQ) as well as of isolated thylakoid membranes, TM (H2O → DCPIP; H2O → PBQ + FeCy) decreased after 24 h of Cd1.0 cultivation to 7 %. Photosystem 1 (PS1) activity was less sensitive to the effect of Cd2+ than PS2 activity. CdCl2 concentration in cultivation media after 24 h of cultivation proved that the cyanobacterium cells take up these ions to a large extent from the cultivation medium. After 24 h of the Cd1.0 treatment only 12 % of the amount of Cd2+ originally added to the cultivation medium was found. The ratio of external-antenna pigments, phycocyanin, and allophycocyanin to Chl increased approximately twofold with growing Cd2+ concentration in the cultivation medium. This ratio was found in both TM and dodecylmaltoside extracts. and E. Tůmová, D. Sofrová.
a1_Chromolaena odorata is a widespread exotic weed in southern China and other regions of the world. To better understand its invasive strategies, we compared leaf pigment contents and gas-exchange traits of the invader with its two coexisting species (native Urena lobata and invasive Bidens pilosa) under combined conditions of irradiance (full, medium, and low) and nitrogen (full, medium, and low) supplies. The chlorophyll (Chl) a+b content of U. lobata was the highest and the Chl a/b ratio of C. odorata was the lowest among the three weed species. In most treatments, leaf pigment, light-saturated photosynthetic rate (P max), and light saturation point (LSP) of all the species increased, while their Chl a/b ratios decreased with the increasing nitrogen. The P max and LSP of U. lobata were greater than those of the coexisting weeds under full irradiance (FI), but significantly declined with the decreasing irradiance. The invasive weeds, especially C. odorata, showed lower P max and LSP under FI, but they showed slight decrease under low irradiance. Compared to U. lobata, C. odorata exhibited the lower light compensation point (LCP) in most treatments, higher LSP under low and medium irradiance, and lower dark respiration rate under FI. In addition, all the three species showed similar responses to different irradiance and nitrogen conditions, mean phenotypic plasticity index (MPPI) of most photosynthetic variables of the two invasive species was lower than that of U. lobata. These results suggested that C. odorata behaved as a facultative shadetolerant weed, being able to grow in moderately sheltered environments; the lower MPPI might be one of the important competitive strategies during its invasion. However, its invasion should be limited to some very shady habitats., a2_In the field, control should be mainly directed against populations growing in the open or nutrient-rich habitats, where its expansion speed could be much faster. Deep shade by intact canopies or luxuriant forests might be an effective barrier against its invasion., G. M. Quan, D. J. Mao, J. E. Zhang, J. F. Xie, H. Q. Xu, M. An., and Obsahuje seznam literatury
Net photosynthetic rate of yellow upper leaves (UL) of Ligustrum vicaryi was slightly, but not significantly higher than that of green lower leaves (LL). Diurnally, maximum photochemical efficiency of photosystem 2, PS2 (Fv/Fm) of LL did not significantly decline but the UL showed fairly great daily variations. Yield of PS2 of UL showed an enantiomorphous variation to the photosynthetically active radiation and was significantly lower than in the LL. Unlike Fv/Fm, the efficiency of energy conversion in PS2 and both non-photosynthetic and photosynthetic quenching did not differ in UL and LL. Significant differences between UL and LL were found in contents of chlorophyll (Chl) a, b, and carotenoids (Car) and ratios of Chl a/b, Chl b/Chl (a+b), and Car/Chl (a+b). Leaf colour dichotocarpism in L. vicaryi was mainly caused by different photon utilization; sunflecks affected the LL. and Y. Q. Yang, X. F. Yi, P. Prasad.
The crop sensitivity to ozone (O3) is affected by the timing of the O3 exposure, by the O3 concentration, and by the crop age. To determine the physiological response to the acute ozone stress, tomato plants were exposed to O3 at two growth stages. In Experiment I (Exp. I), O3 (500 μg m-3) was applied to 30-d-old plants (PL30). In Experiment II (Exp. II), three O3 concentrations (200, 350, and 500 μg m-3) were applied to 51-d-old plants (PL51). The time of the treatment was 4 h (7:30-11:30 h). Photosynthesis and chlorophyll fluorescence measurements were done 4 times (before the exposure; 20 min, 20 h, and 2-3 weeks after the end of the treatment) using a LI-COR 6400 photosynthesis meter. The stomatal pore area and stomatal conductance were reduced as the O3 concentration increased. Ozone induced the decrease in the photosynthetic parameters of tomato regardless of the plant age. Both the photosystem (PS) II operating efficiency and the maximum quantum efficiency of PSII photochemistry declined under the ozone stress suggesting that the PSII activity was inhibited by O3. The impaired PSII contributed to the reduced photosynthetic rate. The greater decline of photosynthetic parameters was found in the PL30 compared with the PL51. It proved the age-dependent ozone sensitivity of tomato, where the younger plants were more vulnerable. Ozone caused the degradation of photosynthetic apparatus, which affected the photosynthesis of tomato plants depending on the growth stage and the O3 concentration., A. A. Thwe, G. Vercambre, H. Gautier, F. Gay, J. Phattaralerphong, P. Kasemsap., and Obsahuje bibliografii
In tomato {Lycopersicon esculentum L.) plants, net carbon dioxide exchange rate (P]si) response curves to both irradiance (/) and short-term [CO2] were similar for plants grown at both 350 and 700 cm3(C02) m'^. However, water vapor conductance (gHjo) of plants grown at high [CO2] was less sensitive to short term [CO2] variations, when measured at low vapor pressure difference, and was larger than the conductance of "ambient [CO2]" plants when both were exposed to high [CO2]. Pn and gHjO under high I increased with temperature over the range 18 to 32 °C. of plants grown in both [CO2] treatments increased at most about 25 % from 350 to 700 cm3 m-3 at 18 and 25 °C, and decreased when exposed to 1000 cm^ m'^ at these temperatures. Thus increasing atmospheric [CO2] might not increase P^ by as much as expected and water use of crops might not decrease.
10-5 M methyl jasmonate (JA-Me) treatment itself did not considerably change the 14CO2 fixation, parameters of room temperature chlorophyll fluorescence induction, proline content, and Na+ as well as Cl- accumulation. Salt stress (30 mM NaCl) lead to a decrease of both 14CO2 fixation and relative water content, and to an increase of proline content. Immediate nonvariable fluorescence (F0) also increased and the variable to maximal fluorescence ratio (Fv/Fm) decreased. Pretreatment with JA-Me for 3 d before salt treatment diminished the inhibitory effect of NaCl on the rate of 14CO2 fixation, protein content, and activity and content of ribulose-1,5-bisophosphate carboxylase/oxygenase. The Na+ and Cl- contents in leaves decreased in JA-Me pretreated plants. The JA-Me pretreatment prevented the increase of F0 level and restored the values of Fv/Fm. and M. Velitchkova, I. Fedina.
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.