ALBERT

Notes: Summary The influence of climatic factors on net photosynthesis, dark respiration and transpiration was investigated in the Negev Desert at the end of the dry summer period when plant water stress was at a maximum. Species studied included: dominant species of the natural vegetation (Artemisia herba-alba, Hammada scoparia, Noaea mucronata, Reaumuria negevensis, Salsola inermis, Zygophyllum dumosum), cultivated plants receiving rainfall and run-off water during the winter season in the run-off farm Avdat (Prunus armeniaca, Vitis vinifera), and irrigated cultivated plants receiving additional water during the summer season (Citrullus colocynthis, Datura metel). 1. Light saturation of net photosynthesis was reached at 60–90 klx conforming to the high solar radiation intensities of the desert. 2. Maximum rates of CO2 uptake per unit of dry weight for the irrigated mesomorphic plants was ten times that of the wild plants. However, in comparison to the other species, maximal rates of CO2 uptake for wild plants were higher when calculated on a leaf area basis than when represented on a dry weight basis. Maximum rates of net photosynthesis per unit chlorophyll content for some of the wild plants (Salsola and Noaea) were comparable to those of the cultivated Vitis and irrigated Citrullus and Datura, Hammada exhibited even higher rates than Prunus. This demonstrates the great photosynthetic capacity of the wild plants even at the end of the dry season. 3. The upper temperature compensation point for net photosynthesis of the wild plants was unusually high as an adaptation to the temperatures of the habitat. Compensation points higher than 49°C exceed the maxima known so far for other flowering species. Maximum rates of net photosynthesis of Hammada were measured when the temperature of the photosynthetic organs was 37°C; at 49°C photosynthesis was only reduced by 50%. 4. Leaf temperature affects plant gas exchange by influencing stomatal aperture. Diffusion resistance of leaves to water vapour was reduced at low temperatures and increased at high temperatures. Reduction of net photosynthesis and transpiration of desert plants at midday may, therefore, be the result of temperature-induced stomatal closure. The possible influence of peristomatal transpiration on stomatal aperture is also discussed. Peristomatal transpiration is directly related to the vapour pressure gradient between the leaf mesophyll and the ambient air which increases with increasing temperatures. 5. Diffusion resistance to water vapour was reduced at high temperatures approaching the limits of heat resistance, due to increased stomatal aperture. This resulted in greater transpirational cooling. 6. Under conditions of increased leaf water stress, diffusion resistance increased, either by sudden stomatal closure at specific threshold values of water stress or through a continuous increase in resistance. This increased resistance is coupled with decreases in transpiration and photosynthesis. 7. In several plant species increased diffusion resistance during the course of the day caused decreased transpiration without a corresponding decrease in photosynthesis. Under these conditions, the ratio of CO2 uptake to transpiration became more favourable as the day progressed. The possibility that this favourable gas exchange response is the result of an increased mesophyll resistance to water vapour loss is discussed.

Notes: Summary Carbon dioxide exchange and transpiration measurements of various wild and cultivated plants were carried out during the dry summer period in 1967 in the Central Negev Desert (Israel). A mobile laboratory used for these investigations is described. Measurements were carried out with conditioned plant chambers which followed either the ambient temperature and humidity or else allowed the experiments to be carried out under constant conditions. The accuracy of the measurements was estimated. The mean error of the determination of the CO2 exchange rate amounts to ±0.07 mg CO2·g-1·h-1. Transpiration rate is measured with an error of ±0.15 g H2O·g-1·h-1. The response time of the instrumentation to reach 90% equilibrium after a change in photosynthesis or transpiration is 7 to 9 minutes. Errors which are caused by changes of quality of incident radiant energy and altered turbulence conditions for the leaves enclosed in the chamber, are discussed.

Notes: Summary The daily course of net photosynthesis and transpiration was measured with temperature and humidity controlled cuvettes at the end of the dry summer season in the Negev Desert. Species studied included: dominant species of the natural vegetation, cultivated plants in the run-off farm Avdat and permanently irrigated plants. An analysis of the influence of single climatic factors on gas exchange was given in part II of this publication. The reactions of the plants to complex changes in all the environmental parameters is the subject of this present study. 1. One-peaked daily courses of net photosynthesis occur in the irrigated species Citrullus colocynthis and Datura metel. After a high rate of net photosynthesis and transpiration before noon CO2 uptake is gradually reduced through stomatal closure even under good soil water conditions. Stomatal closure on C. colocynthis is controlled by the leaf temperatures whereas D. metel closes its stomata due to increasing water stress. 2. Without additional irrigation one-peaked daily courses are only possible with special constitutional adaptations to the extreme climate together with a balanced regulation of water loss. The annual Salsola inermis shows over the whole day no reduction in transpiration. Related to chlorophyll content, CO2 uptake almost attains the rates observed in the irrigated C. colocynthis. It is still unknown what type of water sources are at the disposal of this plant. The perennial chamaephytes Hammada scoparia and Reaumuria negevensis attain a stabilization of net photosynthesis at a lower level through reduction of stomatal water loss and through increased mesophyll resistance to water vapour. This reduces transpiration to a greater degree than CO2 uptake. The stomatal reactions of H. scoparia seem to be mainly controlled by the evaporation conditions in the atmosphere. Related to chlorophyll content in the assimilatory organs, net photosynthesis of both species is higher at noon than in all other chamaephytes. 3. Two-peaked daily courses of net photosynthesis are shown by plants of the run-off farm (Prunus armeniaca and Vitis vinifera). Both have a very high metabolic activity during the morning which is comparable even with that of D. metel and of H. scoparia. At noon, CO2 and H2O exchange is reduced through stomatal closure and falls below the level of all the other plants in the natural vegetation. In apricot, net photosynthesis of vertically oriented leaves does not drop to the compensation point at noon as was found with horizontally oriented leaves which had leaf temperatures some 6–8°C higher. 4. In the natural vegetation, only Noaea mucronata shows gas exchange reactions similar to those of apricot and grapvines. Also N. mucronata has high rates of net photosynthesis in the morning followed by a great reduction of gas exchange through stomatal closure at noon. At a higher water stress this type of an asymmetric two-peaked daily course is changed into a more flat symmetric two peaked curve with low metabolic activity during the morning. In Zygophyllum dumosum and in Artemisia herba-alba the reduction in CO2 uptake at noon is not caused by stomatal closure, but through temperatures above the optimum. The diffusion resistance for water vapour increases steadily during the day. 5. The daily balance of the CO2 exchange is calculated and is compared with the metabolic activity under optimal conditions. The potential photosynthetic capacity of wild plants under optimal conditions is more nearly met under the prevailing desert conditions than in the case with cultivated plants. The effects of the different types of daily courses of gas exchange on the distribution of plants of the Saharo-Arabian region (Reaumuria negevensis, Zygophyllum dumosum) and of plants of the Irano-Turanian vegetation (Hammada scoparia, Artemisia herbaalba) are discussed.

Notes: Zusammenfassung Eine sehr empfindliche und selektive Methode zur spektrophotometrischen Bestimmung des Germaniums unter Verwendung von Brenzcatechinviolett wurde beschrieben. Vor der Bestimmung wird das Germanium zunächst durch Extraktion mit Tributylphosphat (TBP) und Kerosin angereichert und dann mit dem stark basischen Anionenaustauscher Dowex 1, X 8 in einer Mischung aus 30 Vol. %〉 TBP, 60 Vol. % Methylglykol und 10 Vol. % 12-n Salzsäure von den mitextrahierten, die Bestimmung störenden Elementen abgetrennt. Weiters wird gezeigt, daß sich diese Mischung gut eignet, um Uran quantitativ vom Germanium zu trennen. Die spektrophotometrische Bestimmung des Germaniums wird von V(V), Mo(VI), Ga(III), Tl(III), Sb(III), Sn(II) und Fe(III) gestört. Die Störung durch Eisen kann durch Zugabe von Natrium-Kaliumtartrat ausgeschaltet werden.

Notes: Zusammenfassung Auf Grund systematischer Untersuchungen des Verhaltens von Uran in verschiedenen wäßrig-organischen, Tri-n-octylphosphinoxid (TOPO) enthaltenden Lösungsmittelsystemen gegenüber verschiedenen Anionenformen des stark basischen Anionenaustauschers Dowex 1, X 8 wurde eine Methode zur Abtrennung des Urans entwickelt. Bei diesem Verfahren wird das Uran aus einer ascorbin-säurehaltigen, 1-n salzsauren Lösung mit 0,1-m TOPO in Diäthyläther extrahiert und aus einem Gemisch aus 50 Vol. % Äther (0,1-m an TOPO), 45 Vol. % Methylglykol und 5 Vol. % 12-n Salzsäure am Ionenaustauscher (Chloridform) adsorbiert. Nach Elution mit 1-n Salzsäure wird das Uran entweder fluorimetrisch oder spektrophotometrisch nach der Thiocyanatmethode bestimmt. Mit diesem Anionenaustauschverfahren ist eine Abtrennung des Urans von allen, seine fluorimetrische oder spektrophotometrische Bestimmung störenden Ionen und auch vom TOPO selbst möglich. Besonders wurde auf die spektrophotometrische Bestimmung des Urans bei Anwesenheit großer Molybdänmengen eingegangen und eine Methode zur Abtrennung dieses Elementes entwickelt.

Notes: Zusammenfassung Eine Methode zur Abtrennung des Urans wird beschrieben, bei der das Uran aus einer 6-m salzsauren Lösung mit reinem, unverdünntem TBP extrahiert und aus einer Mischung von 30 Vol.% TBP, 60 Vol.% Methylglykol und 10 Vol.% 12-m Salzsäure am stark basischen Anionenaustauscher Dowex 1-X8 (Chloridform) adsorbiert wird. Da der TBP-Extrakt zur Bereitung dieser Mischung verwendet wird, lassen sich Extraktion und Ionenaustausch kombinieren, wodurch nicht nur die Selektivität der Abtrennung des Urans wesentlich erhöht wird, sondern auch eine so weitgehende Anreicherung des Urans auf dem Harz erfolgt, daß auch ppm-Mengen leicht zu bestimmen sind. Das Harz wird zu diesem Zweck zunächst zur Entfernung des TBP mit einer Mischung von 90 Vol.% Methylglykol und 10 Vol.% 12-m Salzsäure, dann zur Entfernung von mitadsorbierten Elementen mit 6-m Salzsäure behandelt; anschließend wird das Uran mit 1-m Salzsäure eluiert und fluorimetrisch bestimmt. Zu Vergleichszwecken wurden 16 geologische Proben nach dieser Methode und auch unter Anwendung einer anderen Anionenaustauschmethode analysiert. Die Ergebnisse zeigen, daß das hier beschriebene Trennverfahren eine quantitative Abtrennung des Urans ermöglicht und zu gut reproduzierbaren Resultaten führt.

Notes: Zusammenfassung Zunächst wird auf die bisher bekannten theoretischen Grundlagen der Ionenaustauschvorgänge speziell in organischen und wäßrig-organischen Medien eingegangen, wobei besonders die für ein selektives Adsorptionsverhalten des Austauschers wichtigen Effekte, wie Quellung, Solvatisierung, unterschiedliche Verteilung organischer Stoffe zwischen Harz- und Lösungsmittelphase, Komplexbildung, Elektroselektivität und Siebeffekt diskutiert werden. Im zweiten Teil wird festgestellt, daß es bei dem Anionenaustauschverhalten verschiedener Elemente in Mischungen aus TBP, Methylglykol und Salzsäure unter Verwendung des stark basischen Anionenaustauschers Dowex 1-X8, Chloridform, zu einer Konkurrenz zweier einander entgegengesetzt wirkender Effekte kommen kann, nämlich des Ionenaustauschs und der Extraktion (KIALE-Effekt). Es konnten Bedingungen gefunden werden, unter denen der eine oder der andere Effekt vorherrscht. Aus dem Adsorptionsverhalten von Uran in Mischungen aus TBP, Methylglykol und Salzsäure und einem inerten Verdünnungsmittel konnten Rückschlüsse auf die Verteilung der einzelnen Komponenten zwischen Harz- und Lösungsmittelphase gezogen und festgestellt werden, daß sich Wasser und Methylglykol hauptsächlich in der hydrophilen polaren Harzphase, aber TBP, Salzsäure und Kerosin hauptsächlich in der unpolaren Lösungsmittelphase anreichern.