Isolated and interactive effects of angular leaf spot (caused by Phaeoisariopsis griseola) and rust (caused by Uromyces appendiculatus) on leaf gas exchange and yield was studied in common bean (Phaseolus vulgaris L. cv. Carioca) plants. Gas exchange was measured on 37, 44, 51, and 58 d after planting using a portable photosynthesis system. The inoculation of plants with P. griseola (P), U. appendiculatus (U), and the combination of both pathogens (P+U) caused a significant reduction of net photosynthetic rate (PN) and yield. The reduction of stomatal conductance (gs), PN, and yield was higher under P and combination of P+U than under U treatment. By effect of U, the reduction on yield was higher than the reductions on gas exchange parameters. On the treatment P+U, a reduction of 23 % in PN and a correspondent reduction of 32 % in yield was observed. The interactive effects of the pathogens on yield could be explained in part by the decreases in gs and in PN of diseased bean leaves. The combined effect of both diseases on yield and gas exchange parameters suggests an antagonistic interaction. and W. C. Jesus Junior ... [et al.].
Responses of baldcypress (Taxodium distichum) seedlings to soil moisture were studied to test the hypothesis that flooding may lead to seedling's higher susceptibility to drought. Treatments included a well-watered but drained control (C), continuously flooded (CF), control followed by drought (CD), and flooded followed by drought (FD). Gas exchange values revealed no significant effects on net photosynthetic rate (PN) in response to flooding. In contrast, after the onset of drought, PN was significantly reduced in CD and FD plants. Significant growth reductions under mild drought conditions indicated that baldcypress seedlings were drought sensitive. However, comparison of gas exchange rates and growth responses between CD and FD plants indicated that prior flooding had no detectable effect on subsequent sensitivity of baldcypress to drought. These findings explain baldcypress persistence in wetland habitats characterized by periodic flooding and mild drought. and J. M. Elcan, S. R. Pezeshki.
Gas exchange, chlorophyll (Chl) fluorescence, and contents of photosynthetic pigments, soluble proteins (ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO), and antioxidant enzymes were characterized in the fully expanded 6th leaves in rice seedlings grown on either complete (CK) or on nitrogen-deficient nutrient (N-deficiency) solutions during a 20-chase period. Compared with the control plants, the lower photosynthetic capacity at saturation irradiance (Pmax) was accompanied by an increase in intercellular CO2 concentration (Ci), indicating that in N-deficient plants the decline in Pmax was not due to stomatal limitation but due to the reduced carboxylation efficiency. The fluorescence parameters ΦPS2, Fv'/Fm', electron transport rate (ETR), and qP showed the same tendency as Pmax in N-deficient plants. Correspondingly, a higher qN paralleled the rise of the ratio of carotenoid (Car) to Chl contents. However, Fv/Fm was still diminished, suggesting that photoinhibition did occur in the photosystem 2 (PS2) reaction centres. In addition, the activities of antioxidant enzymes on a fresh mass basis were gradually lowered, leading to the aggravation of membrane lipid peroxidation with the proceeding N-deficiency. The accumulation of malonyldialdehyde resulted in the lessening of Chl and soluble protein content. Analyses of regression showed PS2 excitation pressure (1 - qP) was linearly correlated with the content of Chl and inversely with soluble protein (particularly RuBPCO) content. There was a lag phase in the increase of PS2 excitation pressure compared to the decrease of RuBPCO content. Therefore, the increased excitation pressure under N-deficiency is probably the result of saturation of the electron transport chain due to the limitation of the use of reductants by the Calvin cycle. Rice plants responded to N-deficiency and high irradiance by decreasing light-harvesting capacity and by increasing thermal dissipation of absorbed energy. and Z.-A. Huang ... [et al.].
The symbiotic association of endophyte fungus, Neotyphodium lolii, and ryegrass improves the ryegrass resistance to drought. This is shown by a 30 % increase in the number of suckers in infected plants (E+), compared to plants lacking endophyte (E-), and by a higher water potential in the E+ than E- plants. The E+ plants have higher stomatal conductance (gs), transpiration rate, net photosynthetic rate (PN), and photorespiratory electron transport rate than the E- plants. The maximal photochemical efficiency (Fv/Fm) and the actual photochemical efficiency (ΦPS2) are not affected by the endophyte fungus. The increase in PN of the E+ plants subjected to water stress was independent from internal CO2 concentration. An increased PN was observed in E+ plants also in optimal water supply. Hence the drought resistance of E+ plants results in increased gs, PN, and photorespiratory electron transport rate. and C. Amalric ... [et al.].
The effect of different doses of nitrogen (N) on gas exchange, relative chlorophyll (Chl) amount, and the content of N in the aerial biomass of lisianthus was evaluated. The treatments consisted of six different concentrations of N (50, 100, 150, 200, 250, and 300 g m-3 noted as N50, N100, N150, N200, N250, and N300, respectively), applied through the fertirrigation technique. N250 and N300 induced increase in the contents of foliar Chl and N in the aerial biomass, that in turn contributed to an increase of photosynthetic activity in lisianthus. and J. A. Marchese ... [et al.].
During mild water stress (decrease of full water capacity from 60 to 35 %) net photosynthetic rate (PN) of four spring barley and wheat genotypes was about twice lower than that for unstressed plants and was mainly limited by non-stomatal factors. Availability of CO2 from intercellular spaces did not change significantly when stomatal conductance (gs) decreased from 0.25-0.35 to 0.15-0.20 mol(H2O) m-2 s-1. There may be two main processes leading to similar intercellular CO2 concentration (ci) in stressed and unstressed seedlings despite of twice lower PN under mild water stress: (a) lower diffusion of CO2 through stomata represented by lower gs, (b) lower consumption of CO2 by photosynthetic apparatus of stressed plants. Last factor is partially pronounced by lower response of PN to ci observed for stressed than for control plants.
Leaf gas exchange of terrestrial and epiphytic orchids from the Atlantic Rainforest in northeast Brazil was investigated under artificial growth conditions. The terrestrial orchids showed higher values of all photosynthetic parameters in comparison to epiphytic ones. There was a close relationship between PN and gs for both terrestrial and epiphytic orchids. Taken together, our results demonstrated that the photosynthetic parameters were related to the specific growth habits of the orchids under study., M. V. Pires ... [et al.]., and Obsahuje bibliografii
Leaf stomatal density (SD), net photosynthetic rates (PN), and stomatal conductance (gs) of Hordeum vulgare and Pisum sativum cultivars in Himalaya increased with altitude. Higher PN and leaf temperature under low CO2 partial pressure at high altitudes could evoke a higher gs and SD to allow sufficient influx of CO2 as well as more efficient leaf cooling through transpiration. and S. K. Vats, N. Kumar, S. Kumar.
Net photosynthetic rate (PN), transpiration rate (E), water use efficiency (WUE), stomatal conductance (gs), and stomatal limitation (Ls) were investigated in two Syringa species. The saturation irradiance (SI) was 400 µmol m-2s-1 for S. pinnatifolia and 1 700 µmol m-2s-1 for S. oblata. Compared with S. oblata, S. pinnatifolia had extremely low gs. Unlike S. oblata, the maximal photosynthetic rate (Pmax) in S. pinnatifoliaoccurred around 08:00 and then fell down, indicating this species was sensitive to higher temperature and high photosynthetic photon flux density. However, such phenomenon was interrupted by the leaf development rhythms before summer. A relatively lower PN together with a lower leaf area and shoot growth showed the capacity for carbon assimilation was poorer in S. pinnatifolia. and H. X. Cui ... [et al.].
The gas-exchange characteristics, leaf water potential and chlorophyll (Chl) a fluorescence of oil palm (Elaeis guineensis Jacq.) seedlings subjected to water stress and recovery were investigated in a greenhouse experiment. At 24 days after imposition of stress, leaf water potential in water-stressed seedlings was doubled compared to that of control and there was a drastic decline in gas-exchange parameters viz. photosynthesis, transpiration, and stomatal conductance. Water stress did not irreversibly affect gas-exchange parameters and quantum efficiency of photosystem II, as seedlings exhibited total recovery of photosynthetic apparatus by 12th day of rehydration. These findings indicate that oil palm exhibits physiological plasticity to water stress during the seedling stage. and K. Suresh ... [et al.].