Theoretical and Experimental Analysis of the 14C Technique and Its Use in Studies of Primary Production

1976 ◽  
Vol 33 (8) ◽  
pp. 1715-1721 ◽  
Author(s):  
Louis A. Hobson ◽  
W. James Morris ◽  
Kathleen T. Pirquet
Keyword(s):  
Environmental Conditions ◽  
Experimental Analysis ◽  
Rate Constants ◽  
Net Photosynthesis ◽  
Field Studies ◽  
Marine Phytoplankton ◽  
Theoretical Studies ◽  
Continuous Irradiation ◽  
Gross Photosynthesis ◽  
Photosynthesis And Respiration

Theoretical and experimental field studies of 14C uptake by marine phytoplankton were carried out to determine environmental conditions required for the technique to measure net photosynthesis. Results of theoretical studies indicate that rapidly metabolizing populations (rate constants for gross photosynthesis and respiration of 0.1 h−1 and 0.007 h−1 respectively) may saturate with 14C after about 30 h of continuous irradiation. Results of field studies indicate that a minimum of 24 h are required for net photosynthesis to be measured when daily irradiations exceed 20 cal cm−2 and nutrient limitation of photosynthesis does not occur. Additional measurements that may be made to aid in interpreting results obtained by the 14C technique are briefly discussed.

Marine Phytoplankton Photosynthesis as a Function of Light Intensity: A Comparison of Methods

1964 ◽  
Vol 21 (1) ◽  
pp. 159-181 ◽  
Author(s):  
C. D. McAllister ◽  
N. Shah ◽  
J. D. H. Strickland
Keyword(s):  
Cell Division ◽  
Skeletonema Costatum ◽  
Algal Growth ◽  
Net Photosynthesis ◽  
Growth Conditions ◽  
Marine Phytoplankton ◽  
Fluorescent Light ◽  
Particulate Carbon ◽  
Gross Photosynthesis ◽  
Light Intensities

An apparatus is described in which the constant for exponential algal growth has been determined as a function of light at controlled temperature. Studies were made of bacteria-free cultures of Skeletonema costatum and Dunaliella tertiolecta grown at the optimum temperature for cell division in media with and without adequate nitrate and phosphate. Less complete studies were made of the behaviour of Monochrysis lutheri and Amphidinium carteri. In all experiments the growth constants were determined at known light intensities, expressed in the energy units, langlies/minute, using light of a known spectral distribution similar to sunlight shining through a few metres of coastal sea water.Growth constants were determined for the following processes: increase of cellular carbon, chlorophylls a, b or c, carotenoids, cell numbers and photosynthesis measured both by oxygen evolution (net and gross) and by the uptake of C-14 labelled carbonate.The rate of maximum photosynthesis occurred when the illumination reached about 0.1 ly/min and little or no light inhibition occurred when the intensity was increased to as high as 0.4 ly/min. Respiration was about 10% of maximum gross photosynthesis. This fraction increased when cells were nitrogen deficient but decreased in phosphate deficient cultures because a phosphate shortage inhibited respiration more severely than photosynthesis.Gross photosynthesis at low light intensities was proportional to the total number of molecules of all plant pigments added together, irrespective of species or of culturing conditions. By contrast, the rate of maximum gross photosynthesis was poorly related to pigment composition, the best correspondence being with the amount of chlorophyll a in the cultures.The uptake rate of C-14 varied with time. There was an apparent "leakage" of labelled organic matter which eventually reached a near-equilibrium with 14CO2 uptake, after which the C-14 method measured the production of particulate carbon but not necessarily net or gross photosynthesis. The rate of particulate carbon production was the same as that of cell division but about 40% less than net photosynthesis in cultures of Skeletonema. Agreement between C-14 rates and net photosynthesis was better in cool-white fluorescent light than in the imitation submarine sunlight used in this work. At high light intensities there was apparently no excretion from Dunaliella "shade" cells but when these became changed to "sun" cells they behaved more like Skeletonema.Various observations are recorded of the effect of growth conditions on cell composition, especially with regard to pigments.The relatively low C-14 rates found with Skeletonema costatum may be explicable in part by an abnormally low counting efficiency for this species even when present as a "weightless" source but the problem requires further study.

scholarly journals Photosynthesis and respiration of the soft coral Xenia umbellata respond to warming but not to organic carbon eutrophication

PeerJ ◽  
2021 ◽  
Vol 9 ◽  
pp. e11663
Author(s):  
Susana Marcela Simancas-Giraldo ◽  
Nan Xiang ◽  
Meghan Moger Kennedy ◽  
Rassil Nafeh ◽  
Edoardo Zelli ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Coral Reefs ◽  
Soft Coral ◽  
Net Photosynthesis ◽  
Ocean Warming ◽  
Soft Corals ◽  
Negative Effects ◽  
Gross Photosynthesis ◽  
Significant Difference ◽  
Photosynthesis And Respiration

Eutrophication with dissolved organic carbon (DOC) as a far under-investigated stressor, and ocean warming, can strongly affect coral reefs and hard corals as major reefs ecosystem engineers. However, no previous studies have investigated the metabolic responses of soft corals to DOC eutrophication, or its interaction with ocean warming. Thus, we investigated respiration and photosynthesis response of Xenia umbellata, a common mixotrophic soft coral from the Indo-pacific, to (1) three levels of DOC eutrophication simulated by glucose addition over the first 21 days of experiment and (2) ocean warming scenarios where the temperature was gradually increased from 26 °C (control condition) to 32 °C over another 24 days in an aquarium experiment. We found no significant difference in response to DOC treatments and all corals survived regardless of the DOC concentrations, whilst subsequent exposure to simulated ocean warming significantly decreased gross photosynthesis by approximately 50% at 30 °C, and 65% at 32 °C, net photosynthesis by 75% at 30 °C and 79% at 32 °C, and respiration by a maximum of 75% at 30 °C; with a slight increase at 32 °C of 25%. The ratio between gross photosynthesis and respiration decreased by the end of the warming period but remained similar between controls and colonies previously exposed to DOC. Our findings suggest that soft corals may be more resistant than hard corals to DOC eutrophication and in consequence, may potentially experiment in less magnitude the negative effects of increased temperature or subsequently both stressors. The results of this study may contribute to explain the successful role of soft corals in phase shifts as reported from many coral reefs. Where predicted declines in reef ecosystems health due to increased eutrophication levels can be exacerbated by future warming.

Effects of pCO2 on photosynthesis and respiration of tropical scleractinian corals and calcified algae

2016 ◽  
Vol 74 (4) ◽  
pp. 1092-1102 ◽  
Author(s):  
S. Comeau ◽  
R. C. Carpenter ◽  
P. J. Edmunds
Keyword(s):  
Dark Respiration ◽  
Net Photosynthesis ◽  
French Polynesia ◽  
Published Data ◽  
Experimental Conditions ◽  
Gross Photosynthesis ◽  
Functional Relationships ◽  
Respiration Rates ◽  
Photosynthesis And Respiration

The effects of ocean acidification (OA) on coral reefs have been studied thoroughly with a focus on the response of calcification of corals and calcified algae. However, there are still large gaps in our knowledge of the effects of OA on photosynthesis and respiration of these organisms. Comparisons among species and determination of the functional relationships between pCO2 and either photosynthesis or respiration are difficult using previously published data, because experimental conditions typically vary widely between studies. Here, we tested the response of net photosynthesis, gross photosynthesis, dark respiration, and light-enhanced dark respiration (LEDR) of eight coral taxa and seven calcified alga taxa to six different pCO2 levels (from 280 to 2000 µatm). Organisms were maintained during 7–10 days incubations in identical conditions of light, temperature, and pCO2 to facilitate comparisons among species. Net photosynthesis was not affected by pCO2 in seven of eight corals or any of the algae; gross photosynthesis did not respond to pCO2 in six coral taxa and six algal taxa; dark respiration also was unaffected by pCO2 in six coral and six algae; and LEDR did not respond to pCO2 in any of the tested species. Overall, our results show that pCO2 levels up to 2000 µatm likely will not fertilize photosynthesis or modify respiration rates of most of the main calcifiers on the back reef of Moorea, French Polynesia.

Ethalfluralin Activity in Cucumber (Cucumis sativus)

Weed Science ◽  
1982 ◽  
Vol 30 (5) ◽  
pp. 498-502 ◽  
Author(s):  
Jeffrey F. Derr ◽  
Thomas J. Monaco
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Weed Control ◽  
Cucumis Sativus ◽  
Environmental Conditions ◽  
Heavy Rain ◽  
Field Studies ◽  
Herbicidal Activity ◽  
Fresh Weight ◽  
Fresh Market

In greenhouse studies, soil organic matter reduced the herbicidal activity of ethalfluralin (N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine). Fifty percent inhibition (I5.0) values for barnyardgrass [Echinochloa crus-galli(L.) Beauv.] stand, injury, and shoot fresh weight increased as the soil organic-matter level increased. No difference in ethalfluralin tolerance was found among 16 cucumber (Cucumis sativusL.) cultivars. When grouped according to market type, fresh market cultivars tended to be injured more than pickling cultivars by excess ethalfluralin. Both shoots and roots of cucumber absorbed the herbicide, but exposure of roots to ethalfluralin was more toxic than exposure of shoots. Field studies indicated that with certain edaphic and environmental conditions, cucumbers can be injured by preemergence applications of ethalfluralin. Injury was greatest in a low organic-matter soil following a heavy rain. Ethalfluralin at 1.3 kg/ha gave adequate weed control in 1 and 3% organic-matter soils, but not in a 9% organic-matter soil.

Biologically effective rate of saflufenacil/dimethenamid-p in soybean (Glycine max)

2012 ◽  
Vol 92 (3) ◽  
pp. 517-531 ◽  
Author(s):  
Robert T. Miller ◽  
Nader Soltani ◽  
Darren E. Robinson ◽  
Trevor E. Kraus ◽  
Peter H. Sikkema
Keyword(s):  
Glycine Max ◽  
Environmental Conditions ◽  
Field Studies ◽  
Effective Rate ◽  
Weed Species ◽  
Green Foxtail ◽  
Equivalent Control ◽  
Lamb’S Quarters ◽  
Set Up ◽  
Annual Weeds

Miller, R. T., Soltani, N., Robinson, D. E., Kraus, T. E. and Sikkema, P. H. 2012. Biologically effective rate of saflufenacil/dimethenamid- in soybean ( Glycine max ). Can. J. Plant Sci. 92: 517–531. A total of five field studies were conducted over a 2-yr period (2009, 2010) at three Ontario locations to determine the biologically effective rate of saflufenacil/dimethenamid-p applied preemergence (PRE) for the control of annual weeds in soybean. The rate of saflufenacil/dimethenamid-p required for the control of annual weeds was influenced by environmental conditions. With adequate moisture and above-average temperatures in 2010, between 224 and 374 g a.i. ha−1 of saflufenacil/dimethenamid-p was required for 80% control of common ragweed, common lamb's quarters, and green foxtail 4 wk after treatment (WAT). In contrast, below-average temperatures and excessive moisture in 2009 resulted in higher rates of saflufenacil/dimethenamid-p being necessary for the same level of weed control. Pigweed species were least affected by environmental conditions after application at 4 WAT with only 245 g a.i. ha−1 required for 80% control in both years. By 11 WAT, 320 g a.i. ha−1 or less of saflufenacil/dimethenamid-p was required to achieve 80% control of these species in 2010, while 845 g a.i. ha−1 or more was needed in 2009 for equivalent control. The potential of saflufenacil/dimethenamid-p as a set-up treatment prior to a postemergence (POST) glyphosate application was also examined. Excellent full season control of all weed species was achieved with saflufenacil/dimethenamid-p applied PRE followed by glyphosate POST. However, there was no difference in yield when saflufenacil/dimethenamid-p was followed by glyphosate POST compared with a single glyphosate POST application.

Response of Gas Exchange in Jointed Goatgrass (Aegilops cylindrica) to Environmental Conditions

Weed Science ◽  
1989 ◽  
Vol 37 (4) ◽  
pp. 562-569 ◽  
Author(s):  
David R. Gealy
Keyword(s):  
Soil Moisture ◽  
Gas Exchange ◽  
Environmental Conditions ◽  
Dark Respiration ◽  
Net Photosynthesis ◽  
Soil Matric Potential ◽  
Dark Respiration Rate ◽  
Matric Potential ◽  
Aegilops Cylindrica ◽  
Jointed Goatgrass

Gas exchange of jointed goatgrass leaves was affected by temperature, irradiance level, and soil matric potential. Net photosynthesis of leaves under saturating irradiance (PPFD3= 1850 (μE·m–2·s−1) was optimum at about 20 C. At 25 C, net photosynthesis was nearly 90% of maximum at a PPFD of 800 μE·m–2·−1. Transpiration, and presumably water use, increased steadily with temperature from 10 to 40 C. Dark respiration rate and compensation points for light and for CO2increased exponentially, or nearly so, from 10 to 40 C. Soil moisture deficits of −130 kPa reduced net photosynthesis and transpiration by about 30 and 55%, respectively, compared to well-watered plants.

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