Water deficit, when rapidly imposed on three C4 grasses of the different metabolic subtypes, Paspalum dilatatum Poiret (NADP-malic enzyme), Cynodon dactylon (L.) Pers (NAD-malic enzyme) and Zoysia japonica Steudel (phosphoenolpyruvate carboxykinase), caused decreases in photosynthetic rates, in the quantum yield of PS II and photochemical quenching, and in the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC). The results provide evidence for non-stomatal limitations of photosynthesis differing in nature between the three species. and A. S. Soares-Cordeiro ... [et al.].
The purpose of this study was to examine how oxygen uptake (V.o2) in decrement-load exercise (DLE) is affected by changing rate of decrease in power output. DLE was performed at three different rates of decrease in power output (10, 20 and 30 watts ・min-1: DLE10, DLE20 and DLE30, respectively) from power output corresponding to 90 % of peak V.o2. V.o2 exponentially increased and then decreased, and the rate of its decrease was reduced at low power output. The values of V.o2 in the three DLE tests were not different for the first 2 min despite the difference in power output. The relationship between V.o2 and power output below 50 watts was obtained as a slope to estimate excessive V.o2 (ex-V.o2) above 50 watts. The slopes were 10.0±0.9 for DLE10, 9.9±0.7 for DLE20 and 10.2±1.0 ml ・min-1 ・ watt-1 for DLE30. The difference between V.o2 estimated from the slope and measured V.o2 was defined as ex-V.o2. The peak value of ex-V.o2 for DLE10 (189±116 ml ・min-1) was significantly greater than those for DLE20 and for DLE30 (93±97 and 88±34 ml ・min-1). The difference between V.o2 in DLE and that in incremental-load exercise (ILE) below 50 watts (ΔV.o2) was greater in DLE 30 and smallest in DLE10. There were significant differences in ΔV.o2 among the three DLE tests. The values of ΔV.o2 at 30 watts were 283±152 for DLE10, 413±136 for DLE20 and 483±187 ml ・min-1 for DLE30. Thus, a faster rate of decrease in power output resulted in no change of V.o2 at the onset of DLE, smaller ex-V.o2 and greater ΔV.o2. These results suggest that V.o2 is disposed in parallel in each motor unit released from power output or recruited in DLE., T. Yano, T. Yunoki, R. Matsuura, T. Arimitsu, T. Kimura., and Obsahuje bibliografii a bibliografické odkazy
An indoor sun simulator was used to provide elevated UV-B radiation (280-315 nm) in combination with realistic ratios to PAR (400-700 nm) and UV-A radiation (315-400 nm) in order to test the physiological response of a soil- and snow microalga during a three-day stress scenario, which may occasionally occur in their respective arctic and alpine habitats.
Chlamydomonas nivalis and Tetracystis sp. are initial colonizers of harsh habitats like summer snow fields and bare arctic soils. The two species were chosen because of their role as primary successors in places where life is generally limited by extreme climatic and nutritional conditions.
The influence of the increased UV-B irradiation (1.43 W m-2; control: 0.52 W m-2) on photosynthesis and pigment composition was measured. Both species survived this incubation without any morphological signs of damage, but oxygen production was reduced by 20-56%. Under control conditions, the amount of chlorophylls (Chls) and carotenoids (Cars) per dry mass increased after three days due to optimal light conditions. After the same period, the treated samples of the soil alga Tetracystis sp. showed a smaller increase in Chls and primary Cars than the control. However, the production of extraplastidal, secondary Cars was induced. On the contrary, the snow alga C. nivalis already had high amounts of secondary Cars before the experiment, and after exposure, all pigment classes increased more compared to control conditions. The results show that these microalgae can tolerate short episodes of enhanced UV-B radiation. Photosynthesis may be temporally impaired, but the cells respond by the production of secondary Cars, which can shield their chloroplasts against excessive irradiation or quench reactive oxygen species. and D. Remias, A. Albert, C. Lütz.
Strong inhibition of rates of CO2 assimilation and transpiration, stomatal conductance, and water use efficiency as well as photosystem 2 (PS2) photochemical activity were related to the severity of reddening. The inhibition of photosynthesis in red cotton leaves was due to both decreased photochemical activity and stomatal limitation. Lowered photosynthetic capacity could be one of the main factors of reduced yield in reddening cotton. and V. Velikova ... [et al.].
One-year-old olive trees (cv. Koroneiki) were grown in plastic containers of 50 000 cm3 under full daylight and 30, 60, and 90 % shade for two years. The effects of shade on leaf morphology and anatomy, including stomatal density and chloroplast structure, net photosynthetic rate (PN), stomatal conductance (gs), and fruit yield were studied. Shade reduced leaf thickness due to the presence of only 1-2 palisade layers and reduced the length of palisade cells and spongy parenchyma. The number of thylakoids in grana as well as in stroma increased as shade increased, while the number of plastoglobuli decreased in proportion to the reduced photosynthetically active radiation (PAR). The higher the level of shade, the lower the stomatal and trichome density, leaf mass per area (ALM), gs, and PN. Shade of 30, 60, and 90 % reduced stomatal density by 7, 16, and 27 %, respectively, while the corresponding reduction in PN was 21, 35, and 67 %. In contrast, chlorophyll a+b per fresh mass, and leaf width, length, and particularly area increased under the same shade levels (by 16, 33, and 81 % in leaf area). PN reduction was due both to a decrease in PAR and to the morphological changes in leaves. The effect of shade was more severe on fruit yield per tree (32, 67, and 84 %) than on PN indicating an effect on bud differentiation and fruit set. The olive tree adapts well to shade compared with other fruit trees by a small reduction in stomatal and trichome density, palisade parenchyma, and a significant increase in leaf area. and K. Gregoriou, K. Pontikis, S. Vemmos.
This paper presents the results of an experimental study to quantify the effects of bed slope and relative submergence on incipient motion of sediment under decelerating flows. Experiments were conducted in an experimental tilting-flume of 8 m long 0.4 m wide and 0.6 m deep with glass-walls. Three uniform sediments with median grain sizes of 0.95, 1.8 and 3.8 mm and three bed slopes of 0.0075, 0.0125 and 0.015 were used under decelerating flow. The main conclusion is that the Shields diagram, which is commonly used to evaluate the critical shear stress, is not suitable to predict the critical shear stress under decelerating flows.
Plant growth, contents of photosynthetic pigments, photosynthetic gas exchange, and chlorophyll (Chl) fluorescence in soybean [Glycine max (L.) Merr. cv. Heinong37] were investigated after it was inoculated with Sinorhizobium fredii USDA191 or treated with 5 mM (NH4)2SO4 (N5) and 30 mM (NH4)2SO4 (N30), respectively. In the plants following N5 fertilization, not only plant biomass, leaf area, and Chl content, but also net photosynthetic rate (PN), stomatal conductance (gs), carboxylation efficiency (CE), maximum photochemical efficiency (Fv/Fm) of photosystem 2 (PS2), and quantum yield of PS2 (ΦPS2) were markedly improved as compared with the control plants. There were also positive effects on plant growth and plant photosynthesis after rhizobia inoculation, but the effects were much less than those of N5 fertilization. For N30 plants there were no significant positive effects on plant growth and photosynthetic capacity. Plant biomass, PN, and gs were similar to those of N-limited (control) plants. ΦPS2 and photochemical quenching (qP) were obviously declined while content of carotenoids and non-photochemical quenching (qN) were significantly enhanced in N30 treated plants. This indicated that excess N supply may cause some negative effects on soybean plants. and X.-J. Zhou ... [et al.].
Roots of six Cucurbitaceae species were exposed to low (14 °C), middle (24 °C), and high (34 °C) temperatures while aerial parts of plants were maintained at ambient temperatures between 23 and 33 °C. The highest dry mass (DM), photon-saturated rate of net photosynthesis (PNsat), and stomatal conductance (gs) were found at 14 °C in figleaf gourd and turban squash plants, at 24 °C in cucumber and melon plants, while bitter melon and wax gourd plants had lower DM, PNsat, and gs at 14 °C than at 24 or 34 °C. Sub-or supra-optimum root temperatures did not induce photoinhibition but induced slight changes in the quantum efficiency of photosystem 2, PS2 (ΦPS2) and photochemical quenching (qp). Meanwhile, xylem sap abscisic acid (ABA) concentration followed a contrasting change pattern to that of gs. Thus the change in PNsat was mainly due to the change in gs and roots played an important role in the regulation of stomatal behaviour by delivering increased amount of ABA to shoots at sub-or supra-optimum root temperatures. and Y. P. Zhang ... [et al.].
The effects of salinity (sea water at 0 ‰ versus 30 ‰) on gross rates of O2 evolution (JO2) and net rates of CO2 uptake (PN) were measured in the halotolerant estuarine C4 grasses Spartina patens, S. alterniflora, S. densiflora, and Distichlis spicata in controlled growth environments. Under high irradiance, salinity had no significant effect on the intercellular to ambient CO2 concentration ratio (Ci/Ca). However, during photosynthesis under limiting irradiance, the maximum quantum efficiency of CO2 fixation decreased under salinity across species, suggesting there is increased leakage of the CO2 delivered to the bundle sheath cells by the C4 pump. Growth under salinity did not affect the maximum intrinsic efficiency of photosystem 2, PS2 (FV/FM) in these species, suggesting salinity had no effect on photosynthesis by inactivation of PS2 reaction centers. Under saline conditions and high irradiance, PN was reduced by 75 % in Spartina patens and S. alterniflora, whereas salinity had no effect on PN in S. densiflora or D. spicata. This inhibition of PN in S. patens and S. alterniflora was not due to an effect on stomatal conductance since the ratio of
Ci/Ca did not decrease under saline conditions. In growth with and without salt, PN was saturated at -500 µmol(quantum) m-2 s-1 while JO2 continued to increase up to full sunlight, indicating that carbon assimilation was not tightly coupled to photochemistry in these halophytic species. This increase in alternative electron flow under high irradiance might be an inherent function in these halophytes for dissipating excess energy. and B. R. Maricle ... [et al.].
In flag leaves of four cultivars of barley (Hordeum vulgare L.) grown in the field under a triple-line-source sprinkler system, that produces a linear soil salinity gradient, a decrease in net carbon dioxide assimilation rate (PN) and stomatal conductance for water vapour (gs) was found. These changes were related to salinity tolerance at moderate salinity. With increasing salinity, PN was saturated at low irradiances and stomatal frequencies increased. A decrease in photosystem 2 (PS2) efficiency was not found in the field after dark adaptation even at high salinity. Salinity induced only small decreases in the actual PS2 efficiency at midday steady-state photosynthesis, indicating that the photosynthetic electron transport was little affected by salinity. Therefore, using PS2 efficiency estimates in attached leaves is probably not a useful tool to screen barley genotypes grown under saline conditions in the field for salinity tolerance. In contrast, excised flag leaves from high salinity plots, once in the laboratory, exhibited a decrease in the variable to maximum chlorophyll fluorescence ratio as compared to excised leaves from control plants. On the other hand, the PN rate might allow for a good discrimination between tolerant and non-tolerant cultivars. and R. Belkhodja ... [et al.].