Diurnal and seasonal changes in photosynthetic characteristics, leaf area dry mass (ADM), and reducing sugar and total chlorophyll (Chl) contents of leaves of Frantoio, Leccino, and Maurino olive cultivars were investigated in Central Italy. Leaf net photosynthetic rate (PN) per unit leaf area changed during the growing season and during the day, but the cultivar did not significantly influence the changes. In both young and one-year-old leaves the highest PN values were observed in October, while the lowest values were recorded in August and December; during the day the highest PN values were generally found in the morning. The pattern of photosynthetic response to photosynthetic photon flux density (PPFD) of leaves was similar in the three genotypes. Sub-stomatal CO2 concentration (CI) tended to increase when PN decreased. The increase in CI was accompanied by a stomatal conductance to water vapor (gS) decrease. In general, PN and dark respiration rate (RD) were correlated. Transpiration rate (E), with no differences between the cultivars, increased from April to July, decreased greatly in August, then increased in October and finally decreased again in December. Leaf water content increased from April to June, remained high until mid July, decreased significantly in August, remaining constant until December with no differences associated with the cultivar. In both young and one-year-old leaves, the leaf water content per unit leaf area was slightly greater in Frantoio than in the other two cultivars. The one-year-old leaves had a higher Chl content than the young ones. The cultivar did not substantially influence the leaf reducing sugar content which decreased from April to August, when it reached the lowest level, then increased rapidly until October. During the day the reducing sugar content did not change significantly. The leaf ADM was slightly higher in Frantoio than in the other cultivars and one-year-old leaves had higher values than the young ones. Leaf ADM decreased from April to June and then tended to increase until December. During the day there were no substantial variations. and P. Proietti, F. Famiani.
Diurnal and seasonal trends in net photosynthetic rate (PN), stomatal conductance (g), transpiration rate (E), vapour pressure deficit, temperature, photosynthetic photon flux density, and water use efficiency (WUE) were compared in a two-year-old Dalbergia sissoo and Hardwickia binata plantation. Mean daily maximum PN in D. sissoo ranged from 21.40±2.60 µmol m-2 s-1 in rainy season I to 13.21±2.64 µmol m-2 s-1 in summer whereas in H. binata it was 20.04±1.20 µmol m-2 s-1 in summer and 13.64±0.16 µmol m-2 s-1 in winter. There was a linear relationship between daily maximum PN and gs in D. sissoo but there was no strong linear relationship between PN and gs in H. binata. In D. sissoo, the reduction in gs led to a reduction in both PN and E enabling the maintenance of WUE during dry season thereby managing unfavourable environmental conditions efficiently whereas in H. binata, an increase in gs causes an increase of PN and E with a significant moderate WUE. and S. G. Saraswathi, K. Paliwal.
The Amazonian peach palm (Bactris gasipaes Kunth) has been grown for heart-of-palm production under subtropical conditions. As we did not see any substantial study on its photosynthesis under Amazonian or subtropical conditions, we carried out an investigation on the diurnal and seasonal variations in photosynthesis of peach palms until the first heart-of-palm harvest, considering their relationship with key environmental factors. Spineless peach palms were grown in 80-L plastic pots, under irrigation. Gas exchange and chlorophyll fluorescence emission measurements were taken in late winter, mid spring, mid summer and early autumn, from 7:00 to 18:00 h, with an additional chlorophyll fluorescence measurement at 6:00 h. The highest net CO2 assimilation (PN), observed in mid summer, reached about 15 μmol m-2 s-1, which was about 20% higher than the maximum values found in autumn and spring, and 60% higher than that in winter The same pattern of diurnal course for PN was observed in all seasons, showing higher values from 8:00 to 9:00 h and declining gradually from 11:00 h toward late afternoon. The diurnal course of stomatal conductance (gs) followed the same pattern of
PN, with the highest value of 0.6 mol m-2 s-1 being observed in February and the lowest one (0.23 mol m-2 s-1) in September. The maximal quantum yield of photosystem II (Fv/Fm) was above 0.75 in the early morning in all the months. The reversible decrease was observed around midday in September and October, suggesting the occurrence of dynamic photoinhibition. A significant negative correlation between the leaf-air vapour pressure difference (VPDleaf-air) and PN and a positive correlation between PN and gs were observed. The photosynthesis of peach palm was likely modulated mainly by the stomatal control that was quite sensible to atmospheric environmental conditions. Under subtropical conditions, air temperature (Tair) and VPDleaf-air impose more significant effects over PN of peach palm than an excessive photosynthetic photon flux density (PPFD). The occurrence of dynamic photoinhibition indicates that under irrigation, peach palms appeared to be acclimated to the full-sunlight conditions under which they have been grown. and M. L. S. Tucci ... [et al.].
Net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), leaf water potential (ψleaf), leaf nitrogen content, and photosynthetic nitrogen use efficiency (PNUE) were compared between a typical C4 plant, Agriophyllum squarrosum and a C3 plant, Leymus chinensis, in Hunshandak Sandland, China. The plant species showed different diurnal gas exchange patterns on June 12-14 when photosynthetic photon flux density (PPFD), air temperature (Tair), and water potential were moderate. PN, E, and
gs of A. squarrosum showed distinct single peak while those of L. chinensis were depressed at noon and had two peaks in their diurnal courses. Gas exchange traits of both species showed midday depression under higher photosynthetic photon flux density (PPFD) and T air when Ψleaf was significantly low down on August 6-8. However, those of A. squarrosum were depressed less seriously. Moreover, A. squarrosum had higher PN, Ψleaf, water use efficiency (WUE), and PNUE than L. chinensis. Thus A. squarrosum was much more tolerant to heat and high irradiance and could utilise the resources on sand area more efficiently than L. chinensis. Hence species like A. squarrosum may be introduced and protected to reconstruct the degraded sand dunes because of their higher tolerance to stress and higher resource use efficiency. and S. L. Niu ... [et al.].
Yields of wheat in semiarid and arid zones are limited by drought, and water condition is very important at each stage of development. Studies carried out at Loess Plateau in the northwestern part of China indicated that yield of spring wheat (Triticum aestivum L.) cv. Dingxi 81-392 was reduced by 41% when subjected to water stress. The effects of two water regimes on net photosynthetic rate (PN), stomatal conductance (gs), and intercellular CO2 concentration (Ci) were investigated at the jointing, booting, anthesis, and grain filling stages. Low soil moisture in comparison to adequate one had invariably reduced PN during the diurnal variations at the four growth stages. PN and gs in both soil moisture regimes was maximally reduced at midday. Ci and the stomatal limitation fluctuated remarkably during photosynthesis midday depression processes, especially at the grain filling stage. Hence atmospheric drought at midday was one of the direct causes inducing stomata closure and the gs depression, but it was beneficial for maintaining stable intrinsic water use efficiency. Fluctuation in Ci implicated that non-stomatal limitation also plays an important role during the period of photosynthesis midday depression. Consequently stomatal and/or non-stomatal limitation are the possible cause of the midday photosynthesis decline. and Xi-ping Deng ... [et al.].
Diurnal variation of gas exchange, chlorophyll (Chl) fluorescence, and xanthophyll cycle components of three maize (Zea mays L.) hybrids released in different years, i.e. Baimaya (1950s), Zhongdan2 (1970s), and Nongda108 (1990s), were compared. On cloudless days, the newer hybrids always had higher net photosynthetic rate (PN), especially at noon, than the older ones. At noon, all the hybrids decreased their maximal yield of photosystem 2 (PS2) photochemistry (Fv/Fm) and actual quantum yield of PS2 (ΦPS2), the newer ones always showing higher values. Generally, the newer hybrids displayed higher photochemical quenching of Chl (qP) and lower non-photochemical quenching (NPQ). The interhybrid differences in PN may be owing to their differential photochemical efficiency. A midday depression in P N occurred in all hybrids, which might be caused by serious photoinhibition or by decreased stomatal conductance. However, midday depression in PN was more obvious in the older hybrids, especially when leaves were senescent. The higher de-epoxidation state of the xanthophylls was noted in older hybrids, which was confirmed by their larger NPQ. The newer maize hybrids did not need a strong de-epoxidation state since they had a better photosynthetic quantum conversion rate and a lower NPQ. and L. Ding ... [et al.].
We hypothesized that decreased stomatal conductance (gs) at elevated CO2 might decrease transpiration (E), increase leaf water potential (ΨW), and thereby protect net photosynthesis rate (PN) from heat damage in maize (Zea mays L) seedlings. To separate long-term effects of elevated CO2, plants grew at either ambient CO2 or elevated CO2. During high-temperature treatment (HT) at 45°C for 15 min, leaves were exposed either to ambient CO2 (380 μmol mol-1) or to elevated CO2 (560 μmol mol-1). HT reduced PN by 25 to 38% across four CO2 combinations. However, the gs and E did not differ among all CO2 treatments during HT. After returning the leaf temperature to 35°C within 30 min, gs and E were the same or higher than the initial values. Leaf water potential (ΨW) was slightly lower at ambient CO2, but not at elevated CO2. This study highlighted that elevated CO2 failed in protecting PN from 45°C via decreasing gs and ΨW., M. N. Qu, J. A. Bunce, Z. S. Shi., and Obsahuje bibliografii
The influence of drought stress (DS) upon whole-plant water content, water relations, photosynthesis, and water-use efficiency of Hibiscus rosa-sinensis cv. Leprechaun (Hibiscus) plants at three levels of potassium (K) nutritional status were determined after a 21-d gradually imposed DS treatment. Compared to K-deficient plants, adequate K supply improved the leaf water content (LWC) and leaf water relations of Hibiscus by decreasing the Ψ π, and generally sustained rates of net photosynthesis (PN) and transpiration (E), and stomatal conductance (gs), both in DS and non-DS plants. In K-deficient Hibiscus, LWC, turgor potential (Ψ P), and PN, E, and gs as well as instantaneous water-use efficiency, WUE (PN/E) were consistently lower, compared to K-sufficient plants. Carbon isotope discrimination (Δ) was lower (i.e. longterm WUE was greatest) in DS than non-DS plants, but K had no effect on Δ during the 21-d drought treatment period under glasshouse conditions. However, the trend in the Δ value of DS plants suggests that Δ could be a useful index of the response of Hibiscus to DS under glasshouse growing conditions. Thus the incorporation of a properly controlled fertilization regime involving sufficient levels of K can improve the acclimation of PN to low Ψleaf, increase PN/E of Hibiscus, and may have potential benefit for other woody plants species. and J. N. Egilla, F. T. Davies Jr., T. W. Boutton.
We investigated the strategies of four co-occurring evergreen woody species Quercus ilex, Quercus coccifera, Pinus halepensis, and Juniperus phoenicea to cope with Mediterranean field conditions. For that purpose, stem water potential, gas exchange, chlorophyll (Chl) fluorescence, and Chl and carotenoid (Car) contents were examined. We recognized two stress periods along the year, winter with low precipitation and low temperatures that led to chronic photoinhibition, and summer, when drought coincided with high radiation, leading to an increase of dynamic photoinhibition and a decrease of pigment content. Summer photoprotection was related to non-photochemical energy dissipation, electron flow to alternative sinks other than photosynthesis, decrease of Chl content, and proportional increase of Car content. Water potential of trees with deep vertical roots (Q. coccifera, Q. ilex, and P. halepensis) mainly depended on precipitation, whereas water potential of trees with shallow roots (J. phoenicea) depended not only on precipitation but also on ambient temperature. and F. J. Baquedano, F. J. Castillo.
An ecophysiological approach was used to determine if competition can be detected among plants in a recently abandoned old-field and in a native tallgrass prairie in northeastern Kansas. In situ photosynthetic parameters and water potentials (Ψ) of target plants were measured 1-2 d after neighbor (intra- and interspecific) removal as well as 1-4 weeks later, and compared with values for plants with neighbors. Only two of the six study species (four old-field and two prairie species) responded to removal of neighboring plants, and only after several weeks had elapsed. Net photosynthetic rates (PN) and stomatal conductances (gs) of Ambrosia trifida in an old-field increased after removal of both intra- and interspecific neighbors. For Apocynum cannabinum, another old-field species, PN of target plants without neighbors was significantly higher than that of target plants with neighbors. For both these species, values of Ψ were not different between target plants with and without neighbors, suggesting that increased availability of nutrients may have been responsible for the observed ecophysiological responses. Though numerous past studies indicate that competition is a major factor influencing plants in old-field and in prairie communities, the experimental approach used in this study revealed that neighbor removal had only limited effects on ecophysiology of the target plants in either community. and F. Norman, C. E. Martin.