In the epiphytic tillandsioids, Guzmania monostachia, Werauhia sanguinolenta, and Guzmania lingulata (Bromeliaceae), juvenile plants exhibit an atmospheric habit, whereas in adult plants the leaf bases overlap and form water-holding tanks. CO2 gas-exchange measurements of the whole, intact plants and δ13C values of mature leaves demonstrated that C3 photosynthesis was the principal pathway of CO2 assimilation in juveniles and adults of all three species. Nonetheless, irrespective of plant size, all three species were able to display features of facultative CAM when exposed to drought stress. The capacity for CAM was the greatest in G. monostachia, allowing drought-stressed juvenile and adult plants to exhibit net CO2 uptake at night. CAM expression was markedly lower in W. sanguinolenta, and minimal in G. lingulata. In both species, low-level CAM merely sufficed to reduce nocturnal respiratory net loss of CO2. δ13C values were generally less negative in juveniles than in adult plants, probably indicating increased diffusional limitation of CO2 uptake in juveniles., J. D. Beltrán ... [et al. ]., and Obsahuje bibliografii
Drought significantly constrains higher yield of alfalfa (Medicago sativa L.) in arid and semiarid areas all over the world. This study evaluated the responses of leaf cuticular wax constituents to drought treatment and their relations to gas-exchange indexes across six alfalfa cultivars widely grown in China. Water deficit was imposed by withholding water for 12 d during branching stage. Cuticular waxes on alfalfa leaves were dominated by primary alcohols (41.7-54.2%), alkanes (13.2-26.9%) and terpenes (17.5-28.9%), with small amount of aldehydes (1.4-3.4%) and unknown constituents (4.5-18.4%). Compared to total wax contents, the wax constituents were more sensitive to drought treatment. Drought decreased the contents of primary alcohol and increased alkanes in all cultivars. Alkane homologs, C25, C27, and C29, were all negatively correlated with photosynthetic rate, transpiration rate, stomatal conductance, and leaf water potential. Under drought conditions, both stomatal and nonstomatal factors were involved in controlling water loss from alfalfa leaves. No direct relationship was observed between wax contents and drought resistance among alfalfa cultivars. An increase in alkane content might be more important in improving drought tolerance of alfalfa under water deficit, which might be used as an index for selecting and breeding drought resistant cultivars of alfalfa., Y. Ni ... [et al.]., and Obsahuje bibliografii
Five decades ago, a novel mode of CO2 assimilation that was later described as C4-photosynthesis was discovered on mature leaves of maize (Zea mays L.) plants. Here we show that 3- to 5-day-old developing maize leaves recapitulate the evolutionary advance from the ancient, inefficient C3 mode of photosynthesis to the C4 pathway, a mechanism for overcoming the wasteful process of photorespiration. Chlorophyll fluorescence measurements documented that photorespiration was high in 3-day-old juvenile primary leaves with non-specialized C3-like leaf anatomy and low in 5-day-old organs with the typical "Kranz-anatomy" of C4 leaves. Photosynthetic gas (CO2)-exchange measurements on 5-day-old leaves revealed the characteristic features of C4 photosynthesis, with a CO2 compensation point close to zero and little inhibition of photosynthesis by the normal oxygen concentration in the air. This indicates a very low photorespiratory activity in contrast to control experiments conducted with mature C3 sunflower (Helianthus annuus L.) leaves, which display a high rate of photorespiration. and U. Kutschera ... [et al.].
The impact of a heterogeneous distribution of actinic light within a leaf chamber for photosynthetic measurements by gas exchange on the photosynthesis-irradiance relationship was investigated. High-resolution light distributions were measured over the area of a commercially available clamp-on leaf chamber equipped with build-in red and blue LEDs, as well as over the area of a custom-made leaf chamber with external light source, using a low-cost digital camera and freely available software. The impact of the measured heterogeneity on the photosynthesis-irradiance response curve was calculated for two realistic scenarios. When the average light intensity over the leaf chamber area was estimated accurately, heterogeneity had minor effects on the photosynthesis-irradiance response curve. However, when the irradiance was measured in the chamber centre, which is common practice, and assumed to be homogeneous, for both leaf chambers the photosynthesis-irradiance response curve was subject to considerable error and led to serious underestimation of the light-limited quantum yield of photosynthesis. Additionally, mixed light sources with different heterogeneity patterns per light source, such as in the clamp-on leaf chamber, potentially increase errors due to heterogeneous physiological responses to light spectrum. High-resolution quantification of the leaf-chamber light distribution enables calculation of the correct average light intensity and already resolves the most pressing problems associated with heterogeneity. To exclude any light-distribution related errors in
gas-exchange measurements a leaf chamber and actinic irradiance source design with a homogeneous light distribution is an absolute requirement. and S. W. Hogewoning ...[et al.].
In China, narrow-wide row planting pattern has been advocated for maize (Zea mays L.) production. However, no previous study has clearly elucidated the complexity of factors affecting maize canopy such as the microclimatic factors, and the effect of photosynthesis in narrow-wide row planting pattern. The current study was undertaken to identify the planting patterns that influence microclimatic conditions and photosynthesis of two maize cultivars (Beiyu288 and Xianyu335) grown in three planting patterns: narrow-wide rows of (1) 30 cm + 170 cm (P1, 6.4 plants m-2), and (2)
40 cm + 90 cm (P2, 6.4 plants m-2), and (3) uniform row of 65 cm (CK, conventional row as control, 6.4 plants m-2). Light interception, temperature, relative humidity (RH), CO2 concentration, and leaf photosynthesis within the canopy were measured in each planting treatment at the grain-filling stage. The net photosynthetic rate
(PN), intercellular CO2 concentration (Ci), stomatal conductance
(gs), transpiration rate (E), and temperature of the narrow-wide row exceeded that of the conventional row. The CO2 concentration and RH of the narrow-wide row were lower than CK by 50 cm strata. The narrow-wide row had a more uniform light intercepted at the whole canopy profile. The results of the current study suggest that
narrow-wide row-planting pattern has a positive effect on canopy microclimate factors and promotes photosynthesis., T. D. Liu, F. B. Song., and Obsahuje bibliografii
a1_Shallow ponds with rapidly photosynthesising cyanobacteria or eukaryotic algae are used for growing biotechnology feedstock and have been proposed for biofuel production but a credible model to predict the productivity of a column of phytoplankton in such ponds is lacking. Oxygen electrodes and Pulse Amplitude Modulation (PAM) fluorometer technology were used to measure gross photosynthesis (PG) vs. irradiance (E) curves (PG vs. E curves) in Chlorella (chlorophyta), Dunaliella salina (chlorophyta) and Phaeodactylum (bacillariophyta). PG vs. E curves were fitted to the waiting-in-line function [PG = (PGmax × E/Eopt) × exp(1 — E/Eopt)]. Attenuation of incident light with depth could then be used to model PG vs. E curves to describe PG vs. depth in pond cultures of uniformly distributed planktonic algae. Respiratory data (by
O2-electrode) allowed net photosynthesis (PN) of algal ponds to be modelled with depth. Photoinhibition of photosynthesis at the pond surface reduced PN of the water column. Calculated optimum depths for the algal ponds were: Phaeodactylum, 63 mm; Dunaliella, 71 mm and Chlorella, 87 mm. Irradiance at this depth is ≈ 5 to 10 μmol m-2 s-1 photosynthetic photon flux density (PPFD). This knowledge can then be used to optimise the pond depth. The total net P N [μmol(O2) m-2 s-1] were: Chlorella, ≈ 12.6 ± 0.76; Dunaliella, ≈ 6.5 ± 0.41; Phaeodactylum ≈ 6.1 ± 0.35. Snell’s and Fresnel’s laws were used to correct irradiance for reflection and refraction and thus estimate the time course of PN over the course of a day taking into account respiration during the day and at night. The optimum PN of a pond adjusted to be of optimal depth (0.1-0.5 m) should be approximately constant because increasing the cell density will proportionally reduce the optimum depth of the pond and vice versa., a2_Net photosynthesis for an optimised pond located at the tropic of Cancer would be [in t(C) ha-1 y-1]: Chlorella, ≈ 14.1 ± 0.66; Dunaliella, ≈ 5.48 ± 0.39; Phaeodactylum, ≈ 6.58 ± 0.42 but such calculations do not take weather, such as cloud cover, and temperature, into account., R. J. Ritchie, A. W. D. Larkum., and Obsahuje bibliografii a dodatky
Athyrium pachyphlebium C. is a popular ornamental fern with considerable shade tolerance. The aim of this study was to investigate how the mature sporophytes acclimate to different light levels and to obtain an optimal light environment for their growth both in natural forest canopy and in urban landscapes. Plant growth and morphology, photosynthetic light-response curves and chlorophyll (Chl) fluorescence were measured at four different light levels (45% full sunlight, 30%, 20% and 8%). As the light intensities declined from 45% to 20%, seedling height, crown growth, foliage number and plant lifespan increased significantly. Seedlings grown at 20% light level were vigorous with great ornamental value. Plants grown in deep shade (8% light) showed severe symptoms of lodging and in 45% full sun, the plants showed highlight-stress symptoms. Seedlings in high light levels exhibited a higher
light-saturated photosynthetic rate (P max), light compensation point (LCP), light saturation point (LSP) and a reduced ability for nonphotochemical quenching (NPQ) of excess light than those in low light levels. However, seedlings in low light exhibited greater efficiency in absorbing and utilizing light energy, characterized by higher chlorophyll b (Chl b) and electron transport rate (ETR). These results indicated that a light level of about 20% full sun appeared to be optimal for A. pachyphlebium when both physiological and morphological performance in the landscape were considered. and D. Huang ... [et al.].
For Tunisian olive tree orchards, nitrogen deficiency is an important nutritional problem, in addition to the availability of water. Establishment of relationships between nutrients such as nitrogen and ecophysiological parameters is a promising method to manage fertilisation at orchard level. Therefore, a nitrogen stress experiment with one-year-old olive trees (Olea europaea L. 'Koroneiki' and 'Meski') was conducted with trees respectively subjected to four nitrogen supply regimes (23.96 meq l-1, 9.58 meq l-1, 4.79 meq l-1 and 0 meq l-1 NO3-).
The current paper focuses on the use of the SPAD-502 portable chlorophyll (Chl) meter, a nondestructive method for fertilisation management under nitrogen stress conditions of olive trees. Maximum net photosynthetic assimilation rates, chlorophyll fluorescence parameters and the SPAD Chl index were therefore measured simultaneously and the Chl and nitrogen content of the leaves were analysed. Significant correlations were established in the olive tree leaves between SPAD-502 readings on the one hand and Chl content, nitrogen content, photosynthetic assimilation rate, and Chl fluorescence parameters (ΦPSII and ETR) on the other hand. and O. Boussadia ... [et al.].
The purpose of this study was to clarify effects of anthocyanins on photosynthesis and photoinhibition in green and red leaves of Oxalis triangularis. Gas analysis indicated that green plants had the highest apparent quantum yield for CO2 assimilation [0.051 vs. 0.031 μmol(CO2) μmol-1(photon)] and the highest maximum photosynthesis [10.07 vs. 7.24 μmol(CO2) m-2 s-1], while fluorescence measurements indicated that red plants had the highest PSII quantum yield [0.200 vs. 0.143 μmol(e-) μmol-1(photon)] and ETRmax [66.27 vs. 44.34 μmol(e-) m-2 s-1]. Red plants had high contents of anthocyanins [20.11 mg g-1(DM)], while green plants had low and undetectable levels of anthocyanin. Red plants also had statistically significantly (0.05>p>0.01) lower contents of xanthophyll cycle components [0.63 vs. 0.76 mg g-1(DM)] and higher activities of the reactive oxygen scavenging enzyme ascorbate peroxidase [41.2 vs. 10.0 nkat g-1(DM)]. Anthocyanins act as a sunscreen, protecting the chloroplasts from high light intensities. This shading effect causes a lower photosynthetic CO2 assimilation in red plants compared to green plants, but a higher quantum efficiency of photosystem II (PSII). Anthocyanins contribute to photoprotection, compensating for lower xanthophyll content in red plants, and red plants are less photoinhibited than green plants, as illustrated by the Fv/Fm ratio. and S. L. Nielsen, A.-M. Simonsen
Stressful environments such as salinity, drought, and high temperature (heat) cause alterations in a wide range of physiological, biochemical, and molecular processes in plants. Photosynthesis, the most fundamental and intricate physiological process in all green plants, is also severely affected in all its phases by such stresses. Since the mechanism of photosynthesis involves various components, including photosynthetic pigments and photosystems, the electron transport system, and CO2 reduction pathways, any damage at any level caused by a stress may reduce the overall photosynthetic capacity of a green plant. Details of the stress-induced damage and adverse effects on different types of pigments, photosystems, components of electron transport system, alterations in the activities of enzymes involved in the mechanism of photosynthesis, and changes in various gas exchange characteristics, particularly of agricultural plants, are considered in this review. In addition, we discussed also progress made during the last two decades in producing transgenic lines of different C3 crops with enhanced photosynthetic performance, which was reached by either the overexpression of C3 enzymes or transcription factors or the incorporation of genes encoding C4 enzymes into C3 plants. We also discussed critically a current, worldwide effort to identify signaling components, such as transcription factors and protein kinases, particularly mitogen-activated protein kinases (MAPKs) involved in stress adaptation in agricultural plants., M. Ashraf, P. J. C. Harris., and Obsahuje bibliografii