Chlorophyll (Chl) fluorescence of warm day/cool night temperature exposed Phalaenopsis plants was measured hourly during 48 h to study the simultaneous temperature and irradiance response of the photosynthetic physiology. The daily pattern of fluorescence kinetics showed abrupt changes of photochemical quenching (qP), non-photochemical quenching (NPQ) and quantum yield of photosystem II electron transport (ΦPSII) upon transition from day to night and vice versa. During the day, the course of ΦPSII and NPQ was related to the air temperature pattern, while maximum quantum efficiency of PSII photochemistry (Fv/Fm) revealed a rather light dependent response. Information on these daily dynamics in fluorescence kinetics is important with respect to meaningful data collection and interpretation. and B. Pollet ... [et al.].
The effects of drought stress induced by polyethylene glycol, PEG (molecular mass 6000) on some ecophysiological characteristics of two wild pistachio species, Mastic and Khinjuk (P. mutica and P. khinjuk) selected as root stocks for production of edible pistachio trees (P. vera) in Iran and Turkey, were studied. Net photosynthetic rate (PN), stomatal conductance (gs), chlorophyll (Chl) fluorescence parameters, leaf water potential (Ψ1), leaf osmotic potential (Ψπ), leaf osmotic adjustment (ΔΨπ), and Chl a and b were measured. All parameters were influenced by increase in concentra-tion of PEG in the nutrient solutions. PN, gs, and Chl a were significantly higher in P. mutica than in P. khinjuk but, compared to the control treatment, P. khinjuk showed a higher resistance to drought stress than P. mutica. and A. Ranjbarfordoei ... [et al.].
Leaf water potential, leaf osmotic potential, chlorophyll a and b contents, stomatal conductance, net photosynthetic rate, and water use efficiency were determined in two pistachio species (Pistacia khinjuk L. and P. mutica L.) grown under osmotic drought stress induced by a combination of NaCl and polyethylene glycol 6000. A decrease in values for all mentioned variables was observed as the osmotic potential of the nutrient solution (Ψs) decreased. The osmotic adjustment (ΔΨπ) of the species increased by decreasing Ψs. Thus P. khinjuk had a higher osmotic drought stress tolerance than P. mutica. and A. Ranjbarfordoei ... [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.].
Characteristic features of stomatal apparatus, i.e, stomatal density, area of the stomatal poruš, relative stomatal area and diffusion resistance (r^) were examined in young (10 d) and old (30 d) leaves of four sugar beet cultivars (Allyx, Arigomono, Monohil and Primahill). Since the plant age was also considered to be an important ontogenetic factor, all measurements were repeated at plant ages of 40, 47, 57 and 65 d. Genotypical differences among the cultivars studied could be explained in terms of the level of ploidy, i,e. an increasing number of chromosome sets was accompanied by an increase of stomatal size and a decrease of stomatal density. The other stomatal characteristics did not significantly differ among the cultivars. The increase in plant age resulted in a higher stomatal density and a gradually decreasing stomatal size. These phenomena generally induced a plant ontogeny controlled increase of the relative stomatal area of all leaf series. Young leaves showed higher stomatal densities, but the stomata were smaller and póre area was reduced by 40 to 60 %, compared to the old leaves. The young leaves also exhibited a smaller r^.
Principal Component Analysis, an ordination technique frequently ušed in phytosociological ecology, has been successfully applied in an attempt to consolidate unknown factors and processes responsible for influencing and modulating photosynthesis determining sugar beet leaf characteristics. Starting from a rough data matrix which consisted of the observed values of 18 cytological, anatomical and ecophysiological leaf parameters, measured in 32 leaf series, this technique calculated the co-ordinates of 32 entities with respect to a whole new set of principál axes. The ordination of all leaf entities was highly correlated with the relative increase of intemal (leaf) area, the total relative stomatal area and the chlorophyll a content. Since their arrangement on the main principál axis was also strongly determined by plant age, the conclusion could be drawn immediately that these three leaf parameters were significantly modulated by plant age. So, conclusions found in a rather subjective way were confirmed by this mathematical ordination technique.
Nowadays, a quest for efficient greenhouse heating strategies, and their related effects on the plant's performance, exists. In this study, the effects of a combination of warm days and cool nights in autumn and spring on the photosynthetic activity and efficiency of Phalaenopsis were evaluated; the latter, being poorly characterised in plants with crassulacean acid metabolism (CAM) and, to our knowledge, not reported before in Phalaenopsis. 24-h CO2 flux measurements and chlorophyll (Chl) fluorescence analyses were performed in both seasons on Phalaenopsis 'Hercules' exposed to relatively constant temperature regimes, 25.5/24.0°C (autumn) and 30/27°C (spring) respectively, and distinctive warm day/cool night temperature regimes, 27/20°C (autumn) and 36/24°C (spring), respectively. Cumulated leaf net CO2 uptake of the distinctive warm day/cool night temperature regimes declined with 10-16% as compared to the more constant temperature regimes, while the efficiency of carbon fixation revealed no substantial differences in both seasons. Nevertheless, a distinctive warm day/cool night temperature regime seemed to induce photorespiration. Although photorespiration is expected not to occur in CAM, the suppression of the leaf net CO2 exchange during Phase II and Phase IV as well as the slightly lower efficiency of carbon fixation for the distinctive warm day/cool night temperature regimes confirms the involvement of photorespiration in CAM. A seasonal effect was reflected in the leaf net CO2 exchange rate with considerably higher rates in spring. In addition, sufficiently high levels of photosynthetically active radiation (PAR) in spring led to an efficiency of carbon fixation of 1.06-1.27% which is about twice as high than in autumn. As a result, only in the case where a net energy reduction between the temperature regimes compensates for the reduction in net CO2 uptake, warm day/cool night temperature regimes may be recommended as a practical sustainable alternative. and B. Pollet ... [et al.].