Twelve randomly chosen Stipa tenacissima L. individuals were grouped into three tussock size classes, small (ST), medium (MT), and large (LT) with 5.6±0.8, 34.1±4.2, and 631.9±85.8 g of dry green foliar matter, respectively, in three plots with different S. tenacissima cover. Instantaneous (WUEi) and long-term (WUEl) water-use efficiencies were measured in two seasons of contrasting volumetric soil water content (early winter 21.0±0.8 % and summer 5.8±0.3 %). Maximum photochemical efficiency of photosystem 2 and stomatal conductance in summer assessed the extent of water and irradiance stress in tussocks of different size. WUEi was lower in MT and ST “water spender” strategies than in LT during the high water-availability season. In summer net photosynthetic rate and WUEi were higher and photoinhibition was lower in LT than in MT and ST. Significant spatial variability was found in WUEi. Water uptake was competitive in stands with denser alpha grass and more water availability in summer, reducing their WUEi. However, WUEl showed a rising tendency when water became scarce. Thus it is important to explicitly account for plant size in ecophysiological studies, which must be combined with demographic information when estimating functional processes at stand level in sequential scaling procedures. and D. A. Ramírez ... [et al.].
2-year-old seedlings of Metasequoia glyptostroboides were grown in open top chambers and exposed to four ozone concentrations [O3] (charcoal-filtered air, CF; 50, 100, and 200 mm3 m-3) for 25 d. Measurements of growth, leaf chlorophyll (Chl) content, and gas exchange parameters were made before and/or after O3 exposure. Leaf length, crown width, Chl a/b, net photosynthetic rate, stomatal conductance, and transpiration rate were significantly reduced at 100 and 200 mm3(O3) m-3. A remarkable decrease in stomatal conductance also occurred at 50 mm3(O3) m-3. and Z.-Z. Feng ... [et al.].
Wheat (Triticum aestivum L.) cv. Jimai22 was used to evaluate the effect of ethylene evolution rate (EER) and 1-aminocyclopropane-1-carboxylic acid (ACC) and their relations with photosynthesis and photochemical efficiency in plants well-watered (WW) and under a severe water deficit (SWD). SWD caused a noticeable reduction in the grain mass. The marked increases in both EER and the ACC concentration were observed under SWD; it was reversed effectively by exogenous spermidine (Spd) or amino-ethoxyvinylglycine (AVG). Thermal images indicated that SWD increased obviously the temperature of flag leaves, mainly due to the decrease in transpiration rate under SWD. Exogenous Spd or AVG decreased to some extent the temperature of the flag leaves. The strong decline in photosynthetic rate (PN) and stomatal conductance as well as the photodamage of PSII were also observed under SWD after 14 and 21 days after anthesis (DAA). Intercellular CO2 concentration was reduced at 7 DAA, but slightly increased at 14 and 21 DAA under SWD, indicating that the decreased PN at 7 DAA might result from stomatal limitations, while the decline after 14 and 21 DAA might be attributed to nonstomatal limitations. Correlation analysis suggested that EER and ACC showed negative relations to photosynthesis and photochemical efficiency. Data obtained suggested that the effects of SWD were mediated predominantly by the increase in EER and ACC concentration, which greatly decreased the leaf photosynthesis and photochemical efficiency, and, therefore, reduced the grain mass. Application of Spd or AVG reduced the EER and ACC, and thus positively influenced photosynthesis and photochemical efficiency under SWD., W. Yang, Y. Yin, W. Jiang, D. Peng, D. Yang, Y. Cui, Z. Wang., and Obsahuje bibliografii
Adjustment in leaf area : mass ratio called leaf area ratio (LAR) is one of the strategies to optimize photon harvesting. LAR was recorded for 10 genotypes of Hevea brasiliensis under high irradiance and low temperature and the genotypes were categorized into two groups, i.e. high LAR and low LAR types. Simultaneously, the growth during summer as well as winter periods, photosynthetic characteristics, and in-vitro oxidative damage were studied. Low LAR (19.86±0.52 m2 kg-1) types, recorded an average of 18.0 % chlorophyll (Chl) degradation under high irradiance and 7.1 % Chl degradation under low temperature. These genotypes maintained significantly higher net photosynthetic rate (PN) of 10.4 μmol(CO2) m-2 s-1 during winter season. On the contrary, the high LAR (24.33±0.27 m2 kg-1) types recorded significantly lower PN of 4 μmol(CO2) m-2 s-1 and greater Chl degradation of 37.7 and 13.9 % under high irradiance and low temperature stress, respectively. Thus LAR may be one of the physiological traits, which are possibly involved in plant acclimation process under both stresses studied. and D. Ray, S. K. Dey, G. Gas.
We compared the responses of sun and shade acclimated saplings of Picea abies and Pinus cembra to excess photosynthetic photon flux density (PPFD) equivalently exceeding the level for saturating net photosynthetic rate (PN). Exposure for 2 h up to 2000 µmol(photon) m-2 s-1 did not affect radiant energy saturated PN. Photoinhibition of photosynthesis was indicated by a small (10 %) reduction of the potential efficiency of photosystem 2 as derived from measurements of chlorophyll fluorescence (FV/FM). However, the extent of FV/FM reduction and half-time for recovery were similar in sun and shade acclimated saplings of both species. Furthermore, the effect on FV/FM was not stronger when the plants were exposed to excess PPFD at 5 °C instead of 15 °C. Frost-hardening of plants increased slightly their resistance to excess PPFD. Establishment of these conifer saplings usually acclimated to shade in their natural habitat may hardly be endangered by a sudden increase of PPFD, e.g., by gap formation. and R. Gamper, S. Mayr, H. Bauer.
How the photosynthetic characteristics of insect-resistant transgenic cotton (Gossypium hirsutum L.) respond to light or whether this genetic transformation could result in unintended effects on their photosynthetic and physiological processes is not well known. Two experiments were conducted to investigate the shapes of net photosynthetic rate (P N), stomatal conductance (g s), apparent light use efficiency (LUEapp) and water use efficiency (WUE) light-response curves for single leaves of Bt (Bacillus thuringiensis) and Bt+CpTI (cowpea trypsin inhibitor) transgenic cotton plants and their non-transgenic counterparts, respectively. Results showed that the significant difference in response of P N and WUE to light between transgenic cotton and non-transgenic cotton occured but not always throughout the growing season or in different experiments or for all transgenic cotton lines. It was highly dependent on growth stage, culture condition and variety, but no obvious difference between any transgenic cotton and non-transgenic cotton in the shapes of g s and LUEapp light-response curves was observed in two experiments at different growth stages. In the field experiments, transgenic Bt+CpTI cotton was less sensitive to response of P N to high irradiance at the boll-opening stage. In pot experiments, WUE light-response curves of both Bt transgenic cotton and Bt+CpTI transgenic cotton progressively decreased whereas non-transgenic cotton slowly reached a maximum at high irradiance at boll-opening stage. We supposed that culture environment could affect the photosynthesis of transgenic cotton both directly and indirectly through influencing either foreign genes expression or growth and physiological processes. and C. X. Sun ... [et al.].
We studied the responses of gas exchange, leaf morphology, and growth to irradiance in Taihangia rupestris, a naturally rare herb inhabiting only vertical cliff faces. In low irradiance (LI, 10 % of full sun) T. rupestris had lower net photosynthetic rate (PN) and produced much less leaves, total leaf area, and biomass than in high (HI, full sun) or medium irradiance (MI, 50 % of full sun). PN of T. rupestris was higher in HI than in MI on August 8, but lower in HI than in MI on September 22. T. rupestris had shorter petioles and lower leaf area ratio, and produced more but smaller and thicker leaves in HI than in MI. In HI the fast production of new leaves may guarantee T. rupestris to maintain higher PN at the whole plant level and thus accumulate more biomass at harvest, although the single-leaf PN may become lower as found on September 22. Hence T. rupestris possesses a latent capacity to acclimate and adapt to full sun. Irradiance, therefore, may not be a responsible factor for the restricted distribution of T. rupestris on vertical cliffs. and Min Tang ... [et al.].
The seasonal variation in photosynthetic rate of grass swards is partly the result of changes in the environment and partly the result of changes in the photosynthetic capacity of the sward itself. We evaluated two types of photosynthesis equations regarding their capacity to analyse seasonal and short-term temperature effects on photosynthesis of ryegrass (Lolium perenne L.). Intact cores of a field-grown ryegrass sward were taken to the laboratory 10 d after cutting for measurement of photosynthesis under controlled conditions. This was done during two four-week periods, in summer and autumn. Net photosynthetic rate (PN) of the sward was lower in autumn than in summer. Both a simple negatively exponential photosynthesis irradiance-response curve and the Farquhar equations for photosynthesis were applied to the in vivo canopy measurements. Application of the irradiance-response curve showed that irradiance-saturated gross photosynthetic rate increased linearly with increasing temperature and was higher in summer than in autumn. The initial radiation use efficiency did not differ between the seasons but decreased with the temperature rise. This explains the observation that total canopy photosynthetic rate decreased after short-term temperature increases in both seasons. The parameters in Farquhar equations that represent the temperature sensitivity of the maximum electron transport rate and of the Michaelis-Menten constants for CO2 and O2 fixation could not be quantified satisfactorily. Parameterisation of the Farquhar equations was hampered by a lack of robust information on many biochemical parameters, and the use of simple empirical response-functions may be preferable in the case of in vivo canopy measurements on grass swards. and B. O. M. Dirks ... [et al.].
Short-term (2 h) treatment with 10 µM abscisic acid decreased stomatal conductance and net photosynthetic rate, and increased carbonic anhydrase activity in pea seedlings. The treatment with 10 µM methyl jasmonate did not significantly affect these parameters. and G. N. Lazova, M. I. Kicheva, L. P. Popova.
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.].