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supplementary layer on the top of the subgrade. As its drainage function is known, this article tries to prove the reinforcement possibility. This layer is relatively thin; nevertheless, it can behave like the geogrids. It is the main path to finding out the opportunity of the interlocking effect and its impact on the railway ballast’s inner shear resistance. Methodology. The laboratory measurements were performed in a multi-level shear box, which allows simulating the multilevel shift of the ballast layer. The tests were planned with and without the CC layer. After shearing, the samples were also tested for load-bearing capacity (E2; according to the Hungarian Standard) and particle breakage. On the other hand, the contact surface between the lowest part of the ballast and CC was also measured by a sophisticated 3D laser scanner (GOM ATOS) and graphically by AutoCAD software. Findings. After the results of the laboratory experiments are analyzed, the following parameters are calculated and determined: 1) the reinforcement ratio as the tangent of the inner shear resistance curves in the 5–15 mm horizontal shearing interval as well as the area under graphs by integration in the 0–40 mm interval; 2) the change in load-bearing capacity of the layer-structure with and without CC; 3) the amount of the cement particles; 4) the amount of the broken particles; 5) contact surface between the lowest layer of ballast and CC; 6) flatness of CC sheets after shearing. Based on the results, the Concrete Canvas provides significant reinforcement to the railway ballast. Originality. Any other type of measurement with Concrete Canvas in a multi-level shear box is unknown. The topic is unique. Practical value. In the future, these results may provide baseline data to verify the suitability of the Concrete Canvas in the railway sub- or superstructure for various types of transport. [ABSTRACT FROM AUTHOR]

Two succulents with similar growth forms but different types of photosynthesis, Cotyledon orbiculata (crassulacean acid metabolism, CAM) and Othonna opima (C3 pathway), were investigated with respect to the modulation of water use efficiency (WUE) during the transition from the rainy season to subsequent drought. Environmental conditions were simulated in a controlled environment experiment on the basis of data collected in the habitat of the two species in the southern Namib desert. Experiments included one or more periods of hot bergwind, which frequently occurs in this region. When water was readily available, daily net CO2 fixation was similar in the two species. This result confirms that the daily CO2 fixation of CAM plants is as high as that of morphologically similar C3plants adapted to the same habitat. As expected, both species reduced CO2 fixation and water loss through transpiration during simulated hot bergwind periods and their WUE values increased. However, after the second hot bergwind period, nearly identical WUEs were recorded: 41.0 and 40.0 mmol mol-1 for C. orbiculata and O. opima, respectively. Therefore the statement that a CAM plant is a better 'water saver' than a C3 plant does not necessarily hold for CAM and C3 plants with similar growth forms growing under the same environmental conditions. [ABSTRACT FROM AUTHOR]

Features of Crassulacean acid metabolism (CAM) were studied in a variety of different succulents in response to climatic conditions between March 1977 and October 1983 in the southern Namib desert (Richtersveld). A screening in 1977 and 1978 revealed that nearly all investigated succulents performed a CAM, but overnight accumulation of malate declined gradually with decreasing soil water potential, tissue osmotic potential, and leaf water content. This was further substantiated by an extended period of insufficient rainfall in 1979 and 1980 which damaged the evergreen CAM succulents between 80 and 100%. In most of the species still living, neither CO-gas exchange nor diurnal acid fluctuation, indicative of CAM, could be detected unless an abundant rainfall restored both CAM features. Plants persisted in a stage of latent life. Water supply is one necessary prerequisite for CAM in the Richtersveld. But even well-watered plants with CAM were sensitive to short-term water stress caused by high water-vapour partialpressure deficit (VPD) in the night, which reduced or prevented CO uptake and resulted in a linear relation between overnight accumulated malate and VPD. The results do not support the opinion that, for the Namib succulents, CAM is an adaptive mechanism to water stress since long-term and short-term water stress stopped nocturnal malate synthesis, but instead lead to the conclusion that nocuturnal CO fixation is only performed when the water status of the plant can be improved simultaneously. [ABSTRACT FROM AUTHOR]

CO2 gas exchange, transpiration and water uptake of the succulent Senecio medley-woodii were monitored simultaneously during a 10 day period of increasing drought. The measurements were performed with a combination of a CO2 gas exchange chamber and a potometer system. Further, leaf water relations and CO2 gas exchange of a branched potted plant were measured during 15 days of water shortage. The enhancement of CO2 dark fixation at the beginning of drought modifies the leaf water relations according to the increased malate accumulation during the dark period. The enhancement of water uptake from dusk to dawn corresponds to the increase of ψleaf during the same period. Therefore at the beginning of drought a short time improvement of plant water status through the increased CO2 dark fixation and malate accumulation can be maintained. [ABSTRACT FROM AUTHOR]

The responses of CO exchange and overnight malate accumulation of leaf and stem succulent CAM-plants to water stress and the particular climatic conditions of fog and föhn in the southern Namib desert have been investigated. In most of the investigated CAM plants a long term water stress gradually attenuated any uptake of external CO and led to CO release throughout day and night. No CAM-idling was observed. Rainfall or irrigation immediately restored daytime CO uptake while the recovery of the nocturnal CO uptake was delayed. Dawn peak of photosynthesis was only found in well watered plants but was markedly reduced by the short term water stress of a föhn-storm. Morning fog with its higher diffuse light intensity compared with clear days increased photosynthetic CO uptake considerably. Even in well watered plants nocturnal CO uptake and malate accumulation were strongly affected by föhn indicating that the water vapour pressure deficit during the night determines the degree of acidification. [ABSTRACT FROM AUTHOR]

The diurnal course of CO gas exchange, CO incorporation, malate and citrate content, and traspiration of Welwitschia mirabilis were measured in one of its natural habitats, the Welwitschia-Vlakte in the central Namib desert (Namibia), in order to decide which CO fixation pathway is used by this gymnosperm. The CO gas exchange of Welwitschia is that of a C plant under arid conditions. Younger leaf parts show a two-peaked pattern of photosynthetic CO uptake whereas in older parts the morning peak is followed by net CO release during the rest of the day. The maximum rates of net photosynthesis decrease from 3.4 μmol m s in 1-year-old parts to 1 μmol m s in 7-year-old parts. No net CO uptake was detected during the night. The diurnal CO balance indicates that the old leaf parts live at the expense of the younger ones. Irrigation of Welwitschia plants resulted in an increased CO uptake throughout the light period with maximum rate of 4.1 μmol m s. CO was only incorporated during the day. The water loss of Welwitschia by transpiration is considerable, reaching a peak value of 1.9 mmol m s around noon. Leaf conductance corresponds with the twopeaked pattern of CO uptake. Although there is no sign of a crassulacean acid metabolism in Welwitschia the leaf contains rather high amounts of malate (up to 200 μmol g dry matter) and citrate (up to 250 μmol g dry matter), which depend on leaf age but do not show any significant day-night oscillation. In spite of all this the δC values are in the range of-17.77 to-19.64‰. Possible reasons for such a high C content in a C plant are discussed. [ABSTRACT FROM AUTHOR]

Welwitschia mirabilis is a perennial desert plant with extremely large leaves (0.5-1.0 m broad, 1-2 m long). Leaf temperatures were measured in the field and the energy budget was calculated. The portions of the leaf which were kept above the ground had leaf temperatures which were only 4-6°C above air temperature. In the leaf portions which were in contact with the ground leaf temperatures were 6-12°C above air temperature (absolute maximum 51°C). The important feature in the energy budget of Welwitschia mirabilis is its high reflectivity (38% of the global radiation). Only about 56% of the global radiation is absorbed by the thick leathery leaves. The energy loss due to convection is of the same order of magnitude as the reflection and it is abouy the same in the portions of leaf on and above the ground. The difference in leaf temperatures found in these portions is due to the loss of thermal radiation from the section of leaf above the ground to the cooler ground which is shaded by the leaf. The provision of a heat sink due to the large area of shade cast by these large leaves is of significance to the existence of Welwitschia mirabilis in its arid habitats. [ABSTRACT FROM AUTHOR]

Juvenile and adult leaves of Piper betle L. were shown to have different spectral properties. A computer model was used to calculate the temperature of these leaves taking the energy balance approach. At high values of solar radiation, juvenile leaves with lower absorptivity in the visible and the near infrared show markedly lower temperatures than mature leaves. There is an ecological effect of high and low leaf temperatures on heat load and water stress. [ABSTRACT FROM AUTHOR]