Ecological significance of net photosynthesis activation by water vapour uptake in Ramalina capitata from rain-protected habitats in central Spain

2002 ◽  
Vol 34 (5) ◽  
pp. 403-413 ◽  
Author(s):  
Ana Pintado ◽  
Leopoldo G. Sancho
Keyword(s):  
Water Content ◽  
Water Vapour ◽  
Liquid Water ◽  
Net Photosynthesis ◽  
Dry Weight ◽  
Central Spain ◽  
Photosynthetic Rates ◽  
Positive Balance ◽  
Water Vapour Uptake ◽  
Water Contents

AbstractThe reactivation of net photosynthesis and dark respiration from water vapour and from liquid water in the lichen Ramalina capitata var. protecta (H. Magn.) Nimis from sheltered habitats in Central Spain was investigated. CO2 gas-exchange response and thallus water content were measured in the laboratory as dry thalli were allowed to equilibrate by water vapour uptake under different relative humidities, and as saturated thalli dried. Water content of thalli from different habitats was also measured in the field during rainfall. The results show that the lichen is very efficient in using water vapour from the air for photosynthesis. Net photosynthetic rates were measured at very low water potentials (up to – 26-9 Megapascal) with water contents of the thalli below 30% dry weight. Maximum net photosynthetic rates measured after water vapour uptake were in some cases similar to those obtained after hydration by liquid water, while respiration rates were always lower after water vapour uptake, indicating a relatively larger activation of the photobiont. Moreover, photosynthetic rates at thallus water contents below 60% dry weight were higher when hydration was achieved through water vapour uptake than with liquid water. Field measurements had shown that this lichen reached water contents through water vapour absorption of 40% dry weight that would allow a positive balance of CO2 uptake. Possible ecological implications of differences in photosynthetic activation depending on the water source are discussed in terms of the carbon gain under natural conditions of this ombrophobous lichen.

Photosynthetic Performance of Two Closely Related Umbilicaria Species in Central Spain: Temperature as a Key Factor

1997 ◽  
Vol 29 (1) ◽  
pp. 67-82 ◽  
Author(s):  
L. G. Sancho ◽  
B. Schroeter ◽  
F. Valladares
Keyword(s):  
Water Content ◽  
Dark Respiration ◽  
Net Photosynthesis ◽  
Dry Weight ◽  
Distribution Patterns ◽  
Photon Flux ◽  
Photosynthetic Response ◽  
Central Spain ◽  
Natural Conditions ◽  
Thallus Water Content

AbstractNet photosynthesis (NP) and dark respiration (DR) of thalli of the lichen species Umbilicaria grisea and U. freyi growing together in the same habitat the Sierra de Guadarrama, central Spain, were measured under controlled conditions in the laboratory and under natural conditions in the field over a range of photosynthetic photon flux densities (PPFD), thallus temperatures and thallus water contents. Laboratory experiments revealed that the photosynthetic response to PPFD at optimum thallus water content is very similar in both species. The light compensation points of NP increased from PPFD of c. 20 µmol m−2 s−1 at 0°C up to c. 100 µmol m−2 s−1 PPFD at 25°C. In both species light saturation was not reached up to 700 µmol m−2 s−1 PPFD except at 0°C. By contrast, the temperature dependence of CO2 gas exchange differed substantially between U. grisea and U. freyi. Both species gave significant rates at 0°C. Optimal temperatures of NP were always higher in U. grisea at various PPFD levels if the samples were kept at optimal thallus water content. NP showed maximal rates at 95% dw in U. grisea and 110% dw in U. freyi respectively. In U. grisea a much stronger depression of NP was observed with only 5% of maximal NP reached at 180% dw. At all PPFD and temperature combinations U. freyi showed higher rates of NP and more negative rates of DR if calculated on a dry weight basis. This was also true under natural conditions at the same site, when U. freyi was always more productive than U. grisea. The differences in the photosynthetic response to temperature between both species correlated well with the different distribution patterns of both species. The possibility of genetic control of the physiological performance of these species and its influence on their distribution patterns and autecology is discussed.

Effects of exposure on water relations and photosynthesis of western hemlock in habitat forms

1976 ◽  
Vol 6 (1) ◽  
pp. 40-48 ◽  
Author(s):  
R. A. Keller ◽  
E. B. Tregunna
Keyword(s):  
Light Intensity ◽  
Water Content ◽  
Water Vapour ◽  
Western Hemlock ◽  
Diffusion Resistance ◽  
The Sun ◽  
Evaporative Demand ◽  
Photosynthetic Rates ◽  
Water Vapour Diffusion ◽  
Vapour Diffusion

Measurements of relative turgidity, transpiration rates, and photosynthetic rates on sun-grown and shade-grown western hemlock (Tsugaheterophylla (Raf.) Sarg.) were used to indicate effects of varying degrees of exposure.The sun-adapted form had low photosynthetic rates but maintained its water content under conditions of high evaporative demand. The shade-adapted form desiccated under exposed conditions, and in contrast with the sun-adapted form, its water vapour diffusion resistance decreased with increasing light intensity.

The response to salinity of a population of Dactyloctenium aegyptium from a saline habitat in southern Nigeria

1994 ◽  
Vol 10 (2) ◽  
pp. 219-228 ◽  
Author(s):  
A. A. Adu ◽  
A. R. Yeo ◽  
O. T. Okusanya
Keyword(s):  
Sea Water ◽  
Nutrient Deficiency ◽  
Net Photosynthesis ◽  
Dry Weight ◽  
Potassium Nitrate ◽  
Inhibitory Effect ◽  
Ion Concentration ◽  
Dactyloctenium Aegyptium ◽  
Sodium And Potassium ◽  
Water Contents

ABSTRACTThe effects of salinity upon the growth, photosynthesis, ion and water contents of a population of Dactyloctenium aegyptium originating from a saline site in Nigeria were investigated. Growth was unaffected by a salinity of 10% artificial sea water, but was reduced by one third in 20% and by two thirds in 30% artificial sea water respectively. Initial adjustment to salinity was due both to increases in the concentrations of sodium and potassium per unit dry weight and to reduced hydration, the latter being the more important at higher salinities. The increase in ion concentration in the cell sap balanced the salinity of the medium at 10% artificial sea water, but was excessive at higher concentrations of sea water. Net photosynthesis was unaffected by 10% artificial sea water but declined at higher salinities. The potassium content of the plants did not fall below 200–250 mM, and the sodium to potassium ratio did not exceed three, even at the highest salinities. Variation in the concentration of nutrients (potassium, nitrate and sulphate) in the medium in the presence of 25% artificial sea water had significant effects upon growth, but these were small in relation to the inhibitory effect of the salinity.The reduction in growth could not be attributed to lack of osmotic adjustment or to nutrient deficiency, and was probably due to ion toxicity within the leaves. The tolerance to reduced hydration, combined with the ability to germinate in saline conditions previously observed, could enable D. aegyptium to establish in a saline soil. The population did not exhibit any halophytic characteristics but did survive with a low growth rate at salinities up to 50% artificial sea water. It is concluded that the species was able to colonize the saline site because of its inherent adaptability, rather than the possession of an ecotype adapted to saline conditions.

scholarly journals Photoautotrophic Micropropagation of Triploid Melon. I: Sucrose, Light, and CO2 Affect Growth and Net Photosynthetic Rates of Shoot Buds

HortScience ◽  
1995 ◽  
Vol 30 (4) ◽  
pp. 752G-753 ◽  
Author(s):  
Jeffrey Adelberg ◽  
Kazuhiro Fujiwara ◽  
Chalermpol Kirdmanee ◽  
Toyoki Kozai
Keyword(s):  
Interactive Effect ◽  
Net Photosynthesis ◽  
Dry Weight ◽  
Photosynthetic Rates ◽  
Shoot Buds ◽  
Light Levels ◽  
Photoautotrophic Micropropagation ◽  
The Media ◽  
L 14 ◽  
Free Media

Growth and net photosynthetic rates of shoots of a triploid melon clone, `(L-14 × B) × L-14', were observed over 21 days following transfer from a multiplication MS medium containing 3% sucrose and 10 μM BA to a shoot development medium containing 1 μM BA at varying levels of sucrose in the medium (0%, 1%, and 3%), and light (50, 100, and 150 PPF) and CO2 (500, 1000, and 1500 ppm) in the headspace. Largest numbers of shoot buds were observed in media with 3% sucrose. Increased light and CO2 had a positive interactive effect. Fresh and dry weights were greatest at highest levels of sucrose, light, and CO2. Although there was less growth in the absence of sucrose, fresh or dry weight of shoot buds grown without sucrose in the media still doubled over the 21 days of culture. Net photosynthetic rates of buds were negative 4 days after initiation of culture and approximately zero after 20 days of treatment. When transferring buds to fresh, sugar-free media, net photosynthetic rates became highly positive. Buds that had been cultured in the absence of sucrose and at highest light levels had the highest net photosynthesis rates upon transfer to fresh, sugar-free media.

Laboratory Studies on the Bionomics of the Rat Fleas, Xenopsylla brasiliensis, Baker, and X. cheopis, Roths

1947 ◽  
Vol 38 (2) ◽  
pp. 263-280 ◽  
Author(s):  
E. B. Edney
Keyword(s):  
Relative Humidity ◽  
Water Vapour ◽  
Dry Weight ◽  
Total Weight ◽  
Laboratory Studies ◽  
Critical Relative Humidity ◽  
Water Contents ◽  
Do So

1. The original purpose of the present work was to confirm a previous finding that, in unfed adult Xenopsylla, longevity varies according to the humidity during the cocoon period, and to find whether this is due to differential loss of water during the prepupal period. The previous finding has been confirmed, but the cause is shown to lie in loss of water during the pupal and not the prepupal period.2. Prepupae are shown to gain in weight by the absorption of water vapour from the air if kept at 24°C. and any relative humidity from 50–90 per cent. If kept below 45 per cent. R.H. they rapidly dry and fail to pupate.3. During this period (about three and a half days from cocoon spinning to pupation at 24°C.) the dry weight decreases by about 2 per cent, of the original total weight, and the total weight increases by from 4–29 per cent., with a mean of 14 per cent.4. The amount of water absorbed is independent of relative humidity within the range 50–90 per cent., and is approximately equal to the increase in total weight.5. The critical relative humidity, below which the insects die and above which they absorb water, is shown to be substantially the same (from 45 to 50 per cent. R.H.) at 12°, 24° and 35°C.6. After pupation the insects begin to lose water and continue to do so throughout the period. The rate of loss increases with decreasing humidity, though the effect of humidity is not very great.7. Adults emerging from pupae kept at higher humidities weigh more, have higher percentage water contents, and live longer without food, than those emerging from pupae kept at lower humidities.8. The results are discussed in the light of previous work, and suggestions as to the mechanism of the process of absorption of water are made.

scholarly journals Modelling evaporation processes of cement-bentonite mixtures

2020 ◽  
Vol 195 ◽  
pp. 02029
Author(s):  
Vincenzo Sergio Vespo ◽  
Gabriele Della Vecchia ◽  
Guido Musso
Keyword(s):  
Water Vapour ◽  
Liquid Water ◽  
Coupled Model ◽  
Degree Of Saturation ◽  
Physical Processes ◽  
Coupled Process ◽  
Model Predictions ◽  
Real Scale ◽  
Water Contents ◽  
Good Agreement

Upon drying, matter and energy are exchanged between the atmosphere and porous media through evaporation, which is a coupled process that involves the simultaneous transport of liquid water, water vapour and heat. At shallow depths, evaporation controls the water content and suction of both natural soils and earthworks, affecting their hydraulic response. This impact is particularly relevant when the earthworks are aimed at the containment of aqueous or non-aqueous pollutants, as in the case of cement bentonite cut-off walls. A coupled model for the transport of liquid water, water vapour and heat through cement bentonite mixtures upon evaporation was formulated. The model considers flow of water driven by both total suction and temperature gradients. Model predictions were compared to experimental results obtained in the laboratory on samples having different sizes and imposed boundary conditions. A good agreement between predicted and measured volumetric water contents was obtained, once defined a suitable dependency of the relative permeability of the mixture on degree of saturation. The results suggest that the proposed formulation correctly accounts for the underlying physical processes, and that it might be used to model the real scale behaviour of cut-off walls.

scholarly journals Morphology and Irrigation Efficiency of Gaura lindheimeri Grown with Capacitance Sensor-controlled Irrigation

HortScience ◽  
2008 ◽  
Vol 43 (5) ◽  
pp. 1555-1560 ◽  
Author(s):  
Stephanie E. Burnett ◽  
Marc W. van Iersel
Keyword(s):  
Water Content ◽  
Nonpoint Source Pollution ◽  
Irrigation System ◽  
Dry Weight ◽  
Nonpoint Source ◽  
Capacitance Sensor ◽  
Set Point ◽  
Phlox Paniculata ◽  
Controlled Irrigation ◽  
Water Contents

Gaura lindheimeri Engelm. & Gray ‘Siskiyou Pink’ (gaura) and Phlox paniculata L. ‘David’ (garden phlox) were grown for 5 weeks in substrates irrigated at volumetric water contents (Θ) of 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, or 0.45 m3·m−3 using a capacitance sensor-controlled irrigation system. Volumetric water contents of the substrate measured by the capacitance sensors controlling irrigation were correlated with measurements with a separate handheld meter (r 2 = 0.83) and with volumetric water content set points throughout the study (r 2 > 0.98). Only 3.8 (at an irrigation set point of 0.10 m3·m−3) to 53 L (0.45 m3·m−3) of water was used to irrigate gaura and phlox and 0 to 7.74 L of this water leached out of the substrates. Significant leaching occurred only at Θ set points of 0.40, or 0.45 m3·m−3. Gaura had shorter and fewer branches and reduced dry weight when grown at lower volumetric water contents, but plants irrigated at set points above 0.25 m3·m−3 were large enough to be marketable. Gaura may be grown with capacitance sensor-automated irrigation using water efficiently and minimizing or eliminating leachate and thus nonpoint source pollution.

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