Werner Koch

Experimentell-ökologische Untersuchungen an Flechten der Negev-Wüste: III. CO2-Gaswechsel und Wasserhaushalt von Krusten- und Blattflechten am natürlichen Standort während der sommerlichen Trockenperiode

Summary CO 2 gas exchange and water relations of crustose and foliose lichens were examined under natural conditions at the end of the dry period in their highland habitat of the Central Negev Desert: Caloplaca ehrenbergii (M uell . A rg .) A. Zahlbr ., Caloplaca aurantia (P ers .) H ellb . var. aurantia P oelt , Lecanora farinosa (F lk .) N yl ., Xanthoria isidioidea (B eltr .) R et G alun , Squamarina cf. crassa (H uds .) P oelt , Diploschistes steppicus R eichert and endolithic lichens inside limestone. Similar to the behaviour of the fruticose species Ramalina maciformis and Teloschistes lacunosus (Part II), the other life forms are also moistened sufficiently, as a result of nightly dew-fall, that an apparent photosynthetic CO 2 uptake is possible for a period of several hours following sunrise. Maximum rates of photosynthesis are peak values compared with known values from field measurements of lichens from other climatic regions. They reach the order of the highest rates of CO 2 assimilation of wild phanerogams, measured at the same time in the same habitat. Also the crustose and the foliose lichens are capable of absorbing enough water vapour in absence of dew condensation from the surrounding moist air at night so as to permit a short period of photosynthetic activity during the morning.

Ecophysiological investigations on wild and cultivated plants in the Negev Desert

SummaryCarbon 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.

Ökophysiologische Untersuchungen an wild- und Kulturpflanzen der Negev-Wüste

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.SummaryThe 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.

Photosynthese von Wüstenflechten am natürlichen Standort nach Wasserdampfaufnahme aus dem Luftraum

* Die Pilzkulturen wurden uns freundlicherweise yon Frau Dr. K A B ~ , Universit~ts-Hautklinik, Herrn Dr. H ~ I ~ E ~ , Inst i tut ffir Pflanzenzfiehtung, GroB-Lfisewitz und yon Herrn Dr. SI~II)EL, Inst i tut ftir Phytopathologie der Universit~t, zur Verfiigung gestellt. [1] SCttMOLLER, H.: Naturwissenschaften 53, 7l t (~966). [2] A s c ~ E g , M.: Bull. Res. Counc. of Israel 6D, 174 (~958). [3] SCHNOLLER, H.: Arch. MikrobioI. 40, 224 (1960).

Kleinklimaanlage zur Messung des pflanzlichen Gaswechsels

folgenden durch GROSSBUCHSTABEN (BLAU, GRtJN, GELB, ROT) gekennzeichnet k6nnte auI folgende Weise durch Wechselwirkungen zwischen den Meldungen der drei Rezeptorarten , ,blau, ,,gri~n und ,,gelb (nach den Wellen1/ingen der Absorptionsmaxima; mit kurs iven Schrifttypen bezeichnet) zustande kommen: Gri inmeldungen (hyperpolarisierend) und Gelbmeldungen (depolarisierend) k6nnten die Grundlage des GR~N-ROT-Gegenfarbensystems sein; Blaumeldungen (hyperpolarisierend) und die S u m m e aus Griin-und Gelbmeldungen (depolarisierend) k6nnten das 13LAU-GELBGegenfarbensystem bilden. Diese Vorstellung steht jedoch nur mit einem Teil der psychophysischen Ph&nomene im Einklang; sic l~13t z.B. unberficksichtigt, dab die Farbenempfindungen am kurzwelligen Ende des sichtbaren Spektrums einen eindeutig nachweisbaren ROT-Gehalt haben. Demgegenfiber ffihrt die folgende, der .corhergehenden ~hnfiche Umrechnung der Absorptionswerte der RezeptorenSehstoffe zu einer ausgezeichneten Ann~herung an die Ergebnisse der psychophysischen Experimente: (Abkfirzung: Pos ~ positive Werte -con . . . ) Pos [blau gelb] N BLAU Pos [gelb blau] ~ GELB Pos [griin { (blau + gelb)~ N GRt3N Pos [w (blau + gelb) griin] ~ ROT.

kophysiologische Untersuchungen an wild- und Kulturpflanzen der Negev-Wste@@@Eco-physiological investigations on wild and cultivated plants in the Negev Desert: II. Die wirkung der auenfaktoren auf CO2-Gaswechsel und transpiration am Ende der Trockenzeit@@@II. The influence of climatic factors on carbon dioxide exchange and transpiration at the end of the dry period

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.SummaryThe 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.ZusammenfassungWährend der Zeit stärkster Wasseranspannung, am Ende der Trockenzeit, wurde der Einfluß der Klimafaktoren auf Nettophotosynthese, Dunkelatmung und Transpiration von Pflanzen in der Negev-Wüste untersucht. Versuchsobjekte waren Wildpflanzen (Artemisia herba-alba, Hammada scoparia, Noaea mucronata, Reaumuria negevensis, Salsola inermis, Zygophyllum dumosum), Kulturpflanzen der Sturzwasserfarm Avdat (Prunus armeniaca, Vitis vinifera) und künstlich bewässerte Arten (Citrullus colocynthis, Datura metel).1.Lichtsättigung der Nettophotosynthese findet entsprechend der ungehinderten Enstrahlung am Wüstenstandort zwischen 60 und 90 klx statt.2.Bei Bezug auf das Trockengewicht der Assimilationsorgane übertreffen die maximalen apparenten Photosyntheseraten der mesomorphen, bewässerten Fflanzen die der Wildpflanzen um das Zehnfache. Im Vergleich zu den übrigen Arten erreichen die Wildpflanzen bei Bezug auf die Oberfläche demgenüber höhere Werte. Bezogen auf den gesamten Chlorophyllgehalt liegen die maximalraten der Nettophotosynthese von Salsola und Noaea in der gleichen Größenordnung wie die von Datura, Citrullus und Wein. Selbst Hammada erreicht höhere Werte als die Aprikose. Daraus wird die hohe Photosynthesefähigkeit der Wildpflanzen am Ende der Trockenzeit deutlich.3.In Anpassung an die Standortstemperaturen liegt der obere Temperaturkompensationspunkt der Nettophotosynthese bei den Wildpflanzen ungewöhnlich hoch. Mit Werten über 49°C erreicht und überschreitet er die bisher für Blütenpflanzen bekannten Maxima. Hammada weist bei 37°C noch optimale Leistungsfähigkeit auf, und bei einer Temperatur der Assimilationsorgane von 49°C ist die Photosyntheserate erst zu 50% gemindert.4.Die Blattemperatur beeinflußt den Gaswechsel der Pflanzen auch durch Einwirkung auf den Spaltöffnungszustand. Temperatursenkung führt zu Verminderung, Temperaturerhöhung zu Steigerung des internen Diffusionswiderstandes der Blätter für Wasserdampf. Die Mittagsdepression von Nettophotosynthese und Transpiration der Wüstenpflanzen kann daher auf einer temperaturgesteuerten Spaltöffnungsreaktion beruhen. Es wird diskutiert, inwieweit auch die bei erhöhter Temperatur gleichzeitig vergrößerte Wasserdampfdruckdifferenz zwischen Blattmesophyll und Umgebungsluft auf dem Wege über die peristomatäre Transpiration Spaltöffnungsregelungen bedingen kann.5.Erhöhung der Temperatur bis in die Nähe der Hitzeresistenzgrenze führt zur Verringerung des Diffusionswiderstandes gegen Wasserdampf, also zu einer Öffnungsreaktion der Stomata. Das verursacht verstärkte Transpirationskühlung.6.Bei zunehmender Wasseranspannung in den Blättern kann der Diffusions-widerstand für Wasserdampf in Form einer Schwellenreaktion durch Spaltenschluß plötzlich steigen, oder es kommt zur einem kontinuierlichen Anstieg, der mit allmählicher Abnahme von Transpiration und Nettophotosynthese verbunden ist.7.Bei vielen Pflanzen zeigt sich im Tageslauf eine Zunahme des Diffusions-widerstandes für Wasserdampf, der eine Abnahme der Transpirationsrate, aber keine Depression der Nettophotosynthese entspricht. Der Quotient zwischen CO2-Aufnahme und Wasserabgabe wird im Laufe des Tages also günstiger. Es wird erwogen, ob dieses für Wüstenpflanzen vorteilhafte Reaktionsvermögen auf einer Erhöhung des Mesophyllwiderstandes für den Transpirationsstrom beruhen kann.