Diurnal patterns of leaf water potential (ΨW), canopy net photosynthetic rate (PN), evapotranspiration rate (E), canopy temperature (Tc), and water use efficiency (WUE) of clusterbean [Cyamopsis tetragonoloba (L.) Taub., cv. Desi] were studied at six phenological stages of plant development under field conditions at CCS Haryana Agricultural University, Hisar. The highest PN, E, and WUE were observed at pod initiation stage (61 DAS). Daily maxima of PN were usually between 11:00 to 14:00 h while those of E and WUE between 12:30 and 16:00 h. PN was mainly dependent on photosynthetically active radiation and E on air temperature (Ta) but the relationships varied at different growth stages. WUE declined with the increase in Ta. At mid-day, ΨW was highest during pod initiation. and A. Kumar ... [et al.].
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.].
Seasonal and daily variations in chlorophyll (Chl) fluorescence were studied in two representative species of Mediterranean grasslands, Tuberaria guttata (an annual) and Chamaemelum nobile (a perennial), in order to assess physiological responses to climatically induced stresses during the growing season. The photochemical efficiency of photosystem (PS) 2 in dark-adapted leaves was measured by the Chl fluorescence ratio Fv/Fp. This ratio decreased progressively from December to July, as the effects of increasing solar radiation and summer drought became more severe. The seasonal decline was observed particularly as a depression of morning and midday values, when photoinhibition was more evident. In both species, the extent of this diurnal depression increased with midday irradiance throughout winter and spring. After sunset, there was complete recovery to optimum values. Towards the end of the life cycle, increased irradiance did not affect the midday decline further but Fv/Fp measurements in the morning and evening never regained their optimum values, indicating the accumulation of photodamage in the reaction centres of PS2. The half-rise time of Fp (T1/2), used to estimate the size of the plastoquinone pool, showed little daily variation in C. nobile throughout the most important part of its seasonal cycle. However, towards the end of its life cycle (June and July) T1/2 values ranged from ca. 200 ms before sunrise to near zero at midday on the same day. The annual species, T. guttata, showed similar disregulation in energy transmission rate both at the seedling stage and at end of its life cycle. Thus seedlings and reproductive plants in particular are sensitive to environmental conditions (extremes of temperature and drought) and cannot maintain consistent electron flow throughout the day. and L. Fernández-Baco ... [et al.].
In order to use rationally switchgrass (Panicum virgatum L.) introduced in a large scale in semiarid regions on the Loess Plateau of China, we investigated and compared soil water storage dynamics, diurnal and seasonal changes in leaf photosynthetic characteristics, and biomass production of switchgrass grown under three different row spacing (20, 40, and 60 cm). Results indicated that photosynthetic parameters showed a pronounced seasonality. Diurnal course of net photosynthetic rate (P N) was bimodal, showing obvious midday depression, which was mainly due to stomatal limitation in May and June, by nonstomatal limitation in August, and both stomatal and nonstomatal factors in September. Generally, P N, stomatal conductance, instantaneous water-use efficiency, light-saturated net photosynthetic rate, saturation irradiance, and compensation irradiance increased with increasing row spacing. Plant height, leaf width, and a relative growth rate of biomass accumulation were significantly higher at the row spacing of 60 cm, while 20 cm spacing showed significantly higher aboveground biomass production and the biomass water-use efficiency. All these confirmed that soil water is the key limiting factor influencing switchgrass photosynthesis, and suggested that the wide row plantation (i.e., 60 cm) was more beneficial to switchgrass growth, while narrow spacing was in favor of improving switchgrass productivity and water-use efficiency., Z. J. Gao, B. C. Xu, J. Wang, L. J. Huo, S. Li., and Obsahuje seznam literatury
To determine what factors limit the growth of wild Fritillaria cirrhosa and Fritillaria delavayi in field conditions, we investigated diurnal changes of the net photosynthetic rate (PN) and the correlation between PN and various environmental factors. Parameters of chlorophyll (Chl) fluorescence were evaluated to test whether ecological fragility caused the extinction of wild F. cirrhosa and F. delavayi. Our study reveals for the first time that F. cirrhosa and F. delavayi did not encounter significant stress under field conditions. A small reduction in maximum photochemical efficiency was observed under high irradiance. The maximum PN of F. cirrhosa was 30 % higher than F. delavayi (p<0.05), and a similar difference was observed for apparent quantum yield (27.3 %, p<0.01). F. delavayi was better adapted to a wide range of irradiances and high environmental temperature. Correlation between PN and environmental factors (without considering the effects of interactions among environmental factors on PN) using leaves of F. cirrhosa revealed that the three primary influencing factors were air pressure (p<0.01), relative humidity (p<0.01), and soil temperature (p<0.05). In F. delavayi, the influencing factors were relative humidity (p<0.01), soil temperature (p<0.05), CO2 concentration (p<0.05), and air pressure (p<0.05). Path analysis (considering effects among environmental factors on PN) showed that air temperature (negative correlation), photosynthetic photon flux density (PPFD) and relative humidity were the three primary limiting factors influencing the growth of F. cirrhosa. For this species, relative humidity reacted indirectly with air pressure, which was reported singularly in other species. Limiting growth factors for F. delavayi were PPFD, air pressure (negative correlation), soil temperature (negative correlation) and air temperature (negative correlation). and Xi-Wen Li, Shi-Lin Chen.
Diurnal variations in net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), internal CO2 concentration (Ci), and water use efficiency (WUE) were studied on individual leaves of coffee plants to determine the effect of climatic factors on photosynthetic capacity. PN and E showed bimodal behaviour with the maximum values of PN at mid-morning. At noon, under saturating photosynthetically active radiation (PAR) and high leaf temperature (Tl), PN declined. In the afternoon (14:00), PN slightly recovered in association with a decrease in Tl and in leaf-to-air vapour pressure deficit (VPD). Reductions in E during the morning were associated with decreases in gs. Higher WUE in the morning was related to higher PN and lower E. The reverse occurred in the afternoon. Goudriaan's simulation model, adapted for coffee canopy photosynthesis, was tested at the level of whole plant (Ppl). Three methods were used: (a) Whole plant net photosynthesis (Ppl) under semi-controlled conditions in a chamber. (b) Ppl estimation following Goudriaan's method (Gaussian integration) of instantaneous PN in single leaves at three canopy depths and at three different hours assuming a photosynthesis unimodal behaviour. (c) Ppl using Goudriaan's method but at five different hours according to the bimodal behaviour reported above. Results of Ppl estimates using Goudriaan's model adapted for coffee canopy confirm the observed Ppl bimodal behaviour with high fitness degree of the measured whole plant photosynthesis. The high fitness found among observed and simulated data indicates that the modified model may be used as a subroutine for the general simulation model of coffee crop growth. and L. F. Gómez ... [et al.].
Diurnal dynamics of photosynthetic character of Angelica sinensis, as well as effect of continuous cropping on leaf photosynthetic character, antioxidant enzyme activity and growth of A. sinensis were investigated under field condition. The results showed that the diurnal net photosynthetic rate of A. sinensis in sunny day exhibited a double-peak pattern, and the peaks occurred at 9:45 and 16:45 h, respectively. There was a significant midday depression with A. sinensis, which was caused principally by stomatal factors such as stomatal conductance. The results also showed that net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), intercellular CO2 concentration (Ci), and chlorophyll content (Chl) of A. sinensis plants under continuous cropping were significantly lower than those of the control. The activity of total superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and growth parameters of A. sinensis plants were significantly decreased under continuous cropping condition. This study provides evidence of continuous cropping obstacle effect on photosynthesis, antioxidant enzyme activity, and growth parameters of A. sinensis in a field experiment, which partly explained the yield reduction of A. sinensis in the field, when it was cultivated continuously on the same soil., X. H. Zhang ... [et al.]., and Obsahuje bibliografii
The diurnal changes in leaf net photosynthetic rate (PN) and sugar and nitrogen contents in wheat [Triticum aestivum (L.) cv. HD 2285] and mungbean [Vigna radiata (L.) Wilczek cv. PS 16] were analysed under ambient, AC [350±25 µmol mol-1] and elevated, EC [600±50 µmol mol-1] CO2 concentrations. In both mungbean and wheat PN of AC- and EC-grown plants compared at the same CO2 concentration showed that PN was higher under EC. However, increased PN in EC-plants declined in the afternoon and approached PN of AC-plants. Depression in PN, however, was less in mungbean compared with the large depression in wheat. Greater down regulation of PN in wheat was associated with the accumulation of large amount of sugars and low nitrogen content in wheat leaves. Mungbean leaves accumulated mostly starch under EC and the difference in N content in AC- and EC-plants was relatively less than in wheat. and A. C. Srivastava ... [et al.].
Diurnal changes in net photosynthetic rate (PN), chlorophyll (Chl) fluorescence, and stomatal aperture of several hybrid poplar clones subjected to midday light stress were measured in July and August of 1996. Midday depression of PN, photosystem 2 (PS2) efficiency, stomatal conductance (gs), and stomatal aperture was observed in all clones, though at differing rates among them. Non-uniform stomatal closure occurred at noon and at other times, requiring a modification of intercellular CO2 concentration (C1). A linear relationship was found between gs and stomatal aperture. More than half of the photons absorbed by PS2 centre dissipated thermally when subjected to light stress at noon. There was a linear relationship between the rate of PS2 photochemical electron transport (PxPFD) and PN. There was a consensus for two fluorescence indicators (1 - qP/qN and (Fm' - F)/Fm') in assessment of susceptibility of photoinhibition in the clones. According to PN, Chl fluorescence, and stomatal aperture, we conclude that midday depression of photosynthesis can be attributed to both stomatal and non-stomatal limitations. and Shouren Zhang, Rongfu Gao.