Showing papers by "Ernst Detlef Schulze published in 1985"

The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content : II. In the mesophytic herbaceous species Helianthus annuus

Abstract: The responses of leaf water potential, leaf conductance, transpiration rate and net photosynthetic rate to vapour pressure deficits varying from 10 to 30 Pa kPa-1 were followed in Helianthus annuus as the extractable soil water decreased. With a vapour pressure deficit of 25 Pa kPa-1 around the entire plant as the soil water content decreased, the leaf conductance and transpiration rate showed a strong closing response to leaf water potential at a value of-0.65 MPa, whereas with a vapour pressure deficit of 10 Pa kPa-1 around the entire plant, the rate of transpiration and leaf conductance decreased almost linearly as the leaf water potential decreased from-0.4 to-1.0 MPa. Increasing the vapour pressure deficit from 10 to 30 Pa kPa-1 in 5 Pa kPa-1 steps decreased the leaf conductance by a similar proportion at all extractable soil water contents. At high soil water contents, the decrease in conductance with leaf water potential was greater when the vapour pressure deficit was increased than when it was not, indicating a direct influence of vapour pressure deficit on the stomata. The rate of net photosynthesis decreased to a smaller degree than the leaf conductance when the vapour pressure deficit around the leaf was varied. Overall, the net photosynthetic rate decreased almost linearly from 20 to 25 μmol m-2 s-1 at-0.3 MPa to 5 μmol m-2 s-1 at-1.2 MPa. As the soil water decreased, the internal carbon dioxide partial pressure was maintained between 14 and 25 Pa.No unique relationship between leaf conductance, transpiration rate or photosynthetic rate and leaf water potential was observed, but in all experiments leaf conductance and the rate of net photosynthesis decreased when about two-thirds of the extractable water in the solid had been utilized irrespective of the leaf water potential. We conclude that soil water status, not leaf water status, affects the stomatal behaviour and photosynthesis of H. annuus.

Canopy transpiration and water fluxes in the xylem of the trunk of Larix and Picea trees - a comparison of xylem flow, porometer and cuvette measurements

Abstract: Leaf gas exchange, transpiration, water potential and xylem water flow measurements were used in order to investigate the daily water balance of intact, naturally growing, adult Larix and Picea trees without major injury. The total daily water use of the tree was very similar when measured as xylem water flow at breast height or at the trunk top below the shade branches, or as canopy transpiration by a porometer or gas exchange chamber at different crown positions. The average canopy transpiration is about 12% lower than the transpiration of a single twig in the sun crown of Larix and Picea. Despite the similarity in daily total water flows there are larger differences in the actual daily course. Transpiration started 2 to 3 h earlier than the xylem water flow and decreased at noon before the maximum xylem water flow was reached, and stopped in the evening 2 to 3 h earlier than the water flow though the stem. The daily course of the xylem water flow was very similar at the trunk base and top below the lowest branches with shade needles. The difference in water efflux from the crown via transpiration and the water influx from the trunk is caused by the use of stored water. The specific capacitance of the crown wood was estimated to be 4.7 x 10-8 and 6.3 x 10-8 kg kg-1 Pa-1 and the total amount of available water storage was 17.8 and 8.7 kg, which is 24% and 14% of the total daily transpiration in Larix and Picea respectively. Very little water was used from the main tree trunk. With increasing transpiration and use of stored water from wood in the crown, the water potential in the foliage decreases. Plant water status recovers with the decrease of transpiration and the refilling of the water storage sites. The liquid flow conductance in the trunk was 0.45 x 10-9 and 0.36 x 10-9 mol m-2s-1 Pa-1 in Larix and Picea respectively. The role of stomata and their control by environmental and internal plant factors is discussed.

Xylem-tapping mistletoes: water or nutrient parasites?

Abstract: Most mistletoes parasitize higher plants by tapping the xylem (a conduction tissue) of their hosts. Field observations of diurnal gas exchange parameters and carbon isotope ratios in xylem-tapping mistletoes from three continents support the hypotheses that water use efficiency and carbon isotope composition are related and that mistletoes which are parasitic for water are also nutrient parasites, differing in their water use efficiency relative to that of their hosts on the basis of host nitrogen supply in the transpiration stream.

The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content : III. In the sclerophyllous woody species Nerium oleander.

Abstract: The responses of leaf conductance, leaf water potential and rates of transpiration and net photosynthesis at different vapour pressure deficits ranging from 10 to 30 Pa kPa-1 were followed in the sclerophyllous woody shrub Nerium oleander L. as the extractable soil water content decreased. When the vapour pressure deficit around a plant was kept constant at 25 Pa kPa-1 as the soil water content decreased, the leaf conductance and transpiration rate showed a marked closing response to leaf water potential at-1.1 to-1.2 MPa, whereas when the vapour pressure deficit around the plant was kept constant at 10 Pa kPa-1, leaf conductance decreased almost linearly from-0.4 to-1.1 MPa. Increasing the vapour pressure deficit from 10 to 30 Pa kPa-1 in 5 Pa kPa-1 steps, decreased leaf conductance at all exchangeable soil water contents. Changing the leaf water potential in a single leaf by exposing the remainder of the plant to a high rate of transpiration decreased the water potential of that leaf, but did not influence leaf conductance when the soil water content was high. As the soil water content was decreased, leaf conductances and photosynthetic rates were higher at equal levels of water potential when the decrease in potential was caused by short-term increases in transpiration than when the potential was decreased by soil drying.As the soil dried and the stomata closed, the rate of photosynthesis decreased with a decrease in the internal carbon dioxide partial pressure, but neither the net photosynthetic rate nor the internal CO2 partial pressure were affected by low water potentials resulting from short-term increases in the rate of transpiration. Leaf conductance, transpiration rate and net photosynthetic rate showed no unique relationship to leaf water potential, but in all experiments the leaf gas exchange decreased when about one half of the extractable soil water had been utilized. We conclude that soil water status rather than leaf water status controls leaf gas exchange in N. oleander.

Control of the rate of cell enlargement: Excision, wall relaxation, and growth-induced water potentials

Abstract: A new guillotine thermocouple psychrometer was used to make continuous measurements of water potential before and after the excision of elongating and mature regions of darkgrown soybean (Glycine max L. Merr.) stems. Transpiration could not occur, but growth took place during the measurement if the tissue was intact. Tests showed that the instrument measured the average water potential of the sampled tissue and responded rapidly to changes in water potential. By measuring tissue osmotic potential (Ψ s ), turgor pressure (Ψ p ) could be calculated. In the intact plant, Ψ s and Ψ p were essentially constant for the entire 22 h measurement, but Ψ s was lower and Ψ p higher in the elongating region than in the mature region. This caused the water potential in the elongating region to be lower than in the mature region. The mature tissue equilibrated with the water potential of the xylem. Therefore, the difference in water potential between mature and elongating tissue represented a difference between the xylem and the elongating region, reflecting a water potential gradient from the xylem to the epidermis that was involved in supplying water for elongation. When mature tissue was excised with the guillotine, Ψ s and Ψ p did not change. However, when elongating tissue was excised, water was absorbed from the xylem, whose water potential decreased. This collapsed the gradient and prevented further water uptake. Tissue Ψ p then decreased rapidly (5 min) by about 0.1 MPa in the elongating tissue. The Ψ p decreased because the cell walls relaxed as extension, caused by Ψ p , continued briefly without water uptake. The Ψ p decreased until the minimum for wall extension (Y) was reached, whereupon elongation ceased. This was followed by a slow further decrease in Y but no additional elongation. In elongating tissue excised with mature tissue attached, there was almost no effect on water potential or Ψ p for several hours. Nevertheless, growth was reduced immediately and continued at a decreasing rate. In this case, the mature tissue supplied water to the elongating tissue and the cell walls did not relax. Based on these measurements, a theory is presented for simultaneously evaluating the effects of water supply and water demand associated with growth. Because wall relaxation measured with the psychrometer provided a new method for determining Y and wall extensibility, all the factors required by the theory could be evaluated for the first time in a single sample. The analysis showed that water uptake and wall extension co-limited elongation in soybean stems under our conditions. This co-limitation explains why elongation responded immediately to a decrease in the water potential of the xylem and why excision with attached mature tissue caused an immediate decrease in growth rate without an immediate change in Ψ p.

Diurnal courses of leaf conductance and transpiration of mistletoes and their hosts in Central Australia

Abstract: In Australia, diurnal courses of leaf conductance and transpiration of hemiparasitic mistletoes (Loranthaceae) and their hosts were measured using steady-state porometers under conditions of partial drought and high evaporative demand. The sites spanned a diversity of climatic regions ranging from the subtropical arid zone with winter rainfall, through the subtropical arid zone with summer rainfall to the tropical summer rainfall zone. With one exception (Acacia farnesiana with deciduous leaves), the hosts were trees or shrubs with evergreen, sclerophyllous leaves or phyllodes.The measurements confirm previous observations that mistletoes transpire at higher rates than their hosts. For adult leaves from all of the 18 different host/mistletoe pairs investigated, the daily average leaf conductances were higher in the parasites than in their hosts. The ratios ranged from 1.5 to 7.9. In the most extreme case,Amyema maidenii had a daily rate of water loss 8.9 times higher than its hostAcacia cowleana. Hoever, the parasites did not exhibit unlimited transpiration. Despite high water loss rates, leaf conductance showed large and consistent changes during the course of the day, indicating definite stomatal regulation. The typical diurnal pattern of conductance in both mistletoes and hosts consisted of an early morning peak followed by a continuous decrease throughout the remainder of the day. There was no abrupt decrease in leaf conductance of the parasites that might be interpreted as a threshold response with respect to internal water potential. In most cases, the continuous stomatal closure occurred without substantial changes in leaf water potential over a time span of several hours. The decrease in leaf conductance was correlated with an increase in leaf-to-air water vapor difference, which was associated with increasing leaf temperatures. It seems probable that external humidity plays a major role in the stomatal response. Diurnal courses of leaf conductance of the host/parasite pairs usually showed similar general patterns, even when the absolute rates were quite different. Thus, mistletoes not only control their water loss by stomatal action but this regulation seems to occur in coordination with the stomatal response of their hosts.The integrated mistletoe/host system must also endure severe drought conditions. Controlled water use is necessary for long-term survival of the host. Assuming stomatal behavior in the host is well adapted to ensure its existence, then similar performance in the mistletoe would promote survival of both host and parasite.

An empirical model of net photosynthesis and leaf conductance for the simulation of diurnal courses of CO2 and H2O exchange

Abstract: An empirical model of CO2 uptake and water loss of leaves is established using steady-state responses of gas exchange to climatic factors as input. From the model the response surface of net CO2 assimilation and leaf conductance to climate can be derived. The model consists of two submodels, one describing the response of CO2 uptake to light and temperature, the other describing the response of leaf conductance to temperature and humidity. Both submodels are joined via the linear relationship between CO2 uptake and leaf conductance at short-term (minutes) variation of irradiance. From the humidity response of leaf conductance and the 'demand function' (Raschke 1979) of CO2 uptake in the mesophyll, the effect of stomata on the diffusion of CO2 between leaf and air is determined. The model is tested by comparing measured and calculated diurnal courses of gas exchange for two plants of Pinus silvestris, differing in photosynthetic capacity due to different levels of magnesium nutrition. Applications and limitations of the model are discussed.

Carbon dioxide assimilation and stomatal response of afroalpine giant rosette plants

Abstract: Maximal rates of CO2 assimilation of 8–11 μmol m-2 s-1 at ambient CO2 concentration were measured for Dendrosenecio keniodendron, D. brassica, Lobelia telekii and L. keniensis during the day in the natural habitat of these plants at 4,200 m elevation on Mt. Kenya. Even at these maximal rates, the CO2 uptake of all species was found to correspond to the linear portion of the CO2 response curve, with a calculated stomatal limitation for CO2 diffusion of 42%. Photosynthesis was strongly reduced at temperatures above 15° C. In contrast to this sensitivity to high temperatures, frozen leaves regained full photosynthetic capacity immediately after thawing. Stomata responded to dry air, but not to low leaf water potentials which occurred in cold leaves and at high transpiration rates. During the day reduced rates of CO2 uptake were associated with reduced light interception due to the erect posture of the rosette leaves and with high temperatures. Stomata closed at vapour pressure deficits which were comparable in magnitude to those characteristic of many lowland habitats (40 mPa Pa-1).

Eine Methode zur raschen Charakterisierung der photosynthetischen Leistungsfähigkeit von Bäumen unter Freilandbedingungen—Anwendung zur Analyse «neuartiger Waldschäden” bei der Fichte

Abstract: GgU~,~NN, E., 1951: Pflanzliche Infektionslehre. Basel: Verlag Birkh~iuser. HACTIc, R, 1874: Hysterium (Hypoderrna) macrosporum R. Hrtg. Der Fichtenritzenschorf. Wichtige Krankheiten der Waldb~iume, S. 101-113. KowAt3•1, T.; LANG, K. J., 1984: Die Pilzflora yon Nadein, Trieben und Asten unterschiedlich alter Fichten (Picea abies [L.] Karst.) mit besonderer Ber/~cksichtigung vom Fichtensterben betroffener Altb~iume. Forstwiss. CbL 103, 349-360. LAN1ER, L.; Jot.v, P.; BONDOUX, P.; BELLEMERr, A-, 1976: Mycologie et Pathologie Foresti6res, II. Pathotogie forestiSre. Paris: Masson Verlag. NEG~, F, W., 1924: Die Krankheiten unserer Waldb~iume. Stuttgart: Enke Vertag. NE6EZ, F. W.; FrotHs, J., 1915: Untersuchungen fiber den Nadelfall der Koniferen. Jahrb. wlss. Botanlk 55, 608-660. NOACK, M, 1928: Ascomycetes. In: Handbuch der Pflanzenkrankhelten. Bd. II. Herausgeber: P. Sorauer. Berlin: Parey Vertag, 575-737. NOBLE, 1893: Uber die Fichtennadelr6te und ihre Verbreitung in den s~ichsischen Forsten. Tharandter Forstl. Jahrb. 43, 39-55. PETR~ql, 04 MOLLEr(, E., I979: Pitzliche Endophyten, am Beispiel vonJuniperus cornmunis. L. Sydowia 32, 224251. RACK, K.; Bu'rtN, H., 1984: Experimenteller Nachweis nadelbewohnender Pilze bel Konlferen. L Fichte (Picea abies). Eur. J. For. Path. 14, 302-310. RrHFUESS, K. E., 1983: Walderkrankungen und tmmlssionen eine Zwischenbilanz. Allgern, Forstz. Nr. 24, 601-610. REHFUESS, K. E.; RODENKmCHrN, H., t984: Uber die Nadetr6te-Erkrankung der Fichte (Picea abies Karst.) in Siiddeutschland. Forstwiss. Cbl. 103, 245-262. Ros-rRUP, E., 1902i Plantepatologi. Det Nordslke Forl., Kopenhaben. SCHWAVeACH, A., 1889: Absterben der Fichte im norddeutschen Kiistengebiete. Z. Forstu. Jagdwesen 21, 608-611.

CO2-Assimilation, Transpiration und Wachstum von Pinus silvestris L. bei unterschiedlicher Magnesiumversorgung

Abstract: Auf magnesiumarmen, quarzreichen sandigen Kiesen westlich von Pressath (Oberpfalz, Bayern) wurde der Einflus der Magnesiumdungung auf den Kohlenstoff- und Wasserhaushalt von 7jahrigen Kiefern untersucht. Bei Mg-Gehalten in den Nadeln unter 0,3 mg pro g Trockengewicht nimmt das Ausmas der Gelbspitzigkeit der Nadeln sowie ihr Starkegehalt deutlich zu, wahrend die Chlorophyll- und Stickstoffgehalte sinken. Nettophotosynthese und Atmung sind, bezogen auf die Gesamtnadel, bei Mg-Mangel verringert. Ebenso ist die Lichtabhangigkeit der Stomataoffnung abgeschwacht. Hiervon abweichend wird die Reaktion der Stomata auf Luftfeuchte nicht vom Mg-Ernahrungszustand beeinflust. Da auch die Wassernachleitung in der Pflanze von der Mg-Versorgung unabhangig ist, haben Mangelpflanzen die gleiche Transpiration und die gleichen Wasserpotentiale wie gedungte Pflanzen. Die verringerte CO2-Aufnahme der Mg-Mangelpflanzen fuhrt aber zu einer Verschlechterung der «Produktivitat der Transpiration» und der Tagesbilanz des CO2-Gewinns. Hohenzuwachs und Langenzuwachs der Zweige sind eingeschrankt. Langerfristig fuhrt ein Absinken des Mg-Gehalts der Nadeln unter 0,3 mg pro g Trockengewicht zum Absterben der Pflanzen.

Mineral concentrations in an autoparasitic phoradendron californicum growing on a parasitic p. californicum and its host, cercidium floridum

Abstract: Tissue concentrations of 12 mineral elements (A1, Ca, Cu, Fe, K, Mg, Mn, amino-N, Na, P, Si, and Zn) were measured in an autoparasitic mistletoe (Phoradendron californicum), the parasitic mistletoe on which it was growing (Phoradendron californicum), and the host tree (Cercidium floridum). Mineral concentrations in the autoparasite were typically 1.1-1.3 times higher than in the parasite. Mineral concentrations of all elements except Ca, Fe, Mg, Mn, and Si were higher in the parasitic mistletoe than its host. Mineral concentration differences are discussed relative to accumulation via the transpiration stream and translocation within the host via the phloem.

The nitrogen balance of Raphanus sativus X raphanistrum plants. I. Daily nitrogen use under high nitrate supply

Abstract: Growth-chamber cultivated Raphanus plants accumulate nitrate during their vegetative growth. After 25 days of growth at a constant supply to the roots of 1 mol m−3 (NO−3) in a balanced nutrient solution, the oldest leaves (eight-leaf stage) accumulated 2.5% NO−3-nitrogen (NO3-N) in their lamina, and almost 5% NO3-N in their petioles on a dry weight basis. This is equivalent to approximately 190 and 400 mol−3 m−3 concentration of NO−3 in the lamina and the petiole, respectively, as calculated on a total tissue water content basis. Measurements were made of root NO−3 uptake, NO−3 fluxes in the xylem, nitrate uptake by the mesophyll cells, and nitrate reduction as measured by an in vivo test. NO−3 uptake by roots and mesophyll cells was greater in the light than in the dark. The NO−3 concentration in the xylem fluid was constant with leaf age, but showed a distinct daily variation as a result of the independent fluxes of root uptake, transpiration and mesophyll uptake. NO−3 was reduced in the leaf at a higher rate in the light than in the dark. The reduction was inhibited at the high concentrations calculated to exist in the mesophyll vacuoles, but reduction continued at a low rate, even when there was no supply from the incubation medium. Sixty-four per cent of the NO−3 influx was turned into organic nitrogen, with the remaining NO−3 accumulating in both the light and the dark.