Development of methods to measure virus inactivation in fresh waters

This study concerns the identification and correction of deficiencies in methods used to measure inactivation rates of enteric viruses seeded into environmental waters. It was found that viable microorganisms in an environmental water sample increased greatly after addition of small amounts of nutrients normally present in the unpurified seed virus preparation. This burst of microbial growth was not observed after seeding the water with purified virus. The use of radioactively labeled poliovirus revealed that high percentages of virus particles, sometimes greater than 99%, were lost through adherence to containers, especially in less turbid waters. This effect was partially overcome by the use of polypropylene containers and by the absence of movement during incubation. Adherence to containers clearly demonstrated the need for labeled viruses to monitor losses in this type of study. Loss of viral infectivity in samples found to occur during freezing was avoided by addition of broth. Finally, microbial contamination of the cell cultures during infectivity assays was overcome by the use of gentamicin and increased concentrations of penicillin, streptomycin, and amphotericin B.     

Development of methods to measure virus inactivation in fresh waters.

This study concerns the identification and correction of deficiencies in methods used to measure inactivation rates of enteric viruses seeded into environmental waters. It was found that viable microorganisms in an environmental water sample increased greatly after addition of small amounts of nutrients normally present in the unpurified seed virus preparation. This burst of microbial growth was not observed after seeding the water with purified virus. The use of radioactively labeled poliovirus revealed that high percentages of virus particles, sometimes greater than 99%, were lost through adherence to containers, especially in less turbid waters. This effect was partially overcome by the use of polypropylene containers and by the absence of movement during incubation. Adherence to containers clearly demonstrated the need for labeled viruses to monitor losses in this type of study. Loss of viral infectivity in samples found to occur during freezing was avoided by addition of broth. Finally, microbial contamination of the cell cultures during infectivity assays was overcome by the use of gentamicin and increased concentrations of penicillin, streptomycin, and amphotericin B.     

The effects of some inhibitors on the rates of photosynthesis and respiration by Chlorella

The effects of several inhibitors on the rates of photosynthesis and of respiration by Chlorella pyrenoidosa have been studied. The inhibitors used in this study include potassium cyanide, hydroxylamine hydrogen chloride, dinitrophenol,and sodium azide. Each inhibitor seems to have its own characteristic action in photosynthesis and in respiration. With the exception of hydroxylamine, all the inhibitors show a stimulation of respiration at low concentrations of the inhibitors. Only dinitrophenol inhibits respiration to a marked extent. Potassium cyanide, hydroxylamine, and dinitrophenol are about equally effective in inhibiting photosynthesis, but sodium azide is nearly ten times as effective.     

Improved methods for the measurement of dissolved and particulate organic carbon in fresh water and their application to chalk streams

The development and use of an improved automatic system for the accurate measurement of dissolved organic carbon (D.O.C.) in fresh waters is described. The method, which covers the range 0-25 mgl^?1 D.O.C., is based on the oxidation of organic carbon to carbon dioxide by U.V. radiation. The carbon dioxide produced is measured by a non dispersive infra-red gas analyser (I.R.G.A.). The I.R.G.A. is also used in the semi-automatic measurement of particulate organic carbon (P.O.C.) by a combustion method which allows very low concentrations to be measured using samples of 200 ml or less. Results of surveys of two river systems indicate that D.O.C. concentrations of less than 2.0 mg l^?1 are typical in unpolluted chalk streams. D.O.C. concentrations of streams draining acid heathland were found to be significantly higher (3-5.5 mg l^?1). D.O.C. concentration was found to increase rapidly during a spate, in a river draining areas of mixed underlying geology. The throughput of D.O.C. during the twenty-five to fifty spates which occur annually in the river could amount to 20-30% of the annual flux of D.O.C. P.O.C. concentration in chalk spring waters (0.03–0.04 mg l^?1) were found to be higher than expected from preliminary estimates using membrane filtration techniques. The relevance of the measurement of D.O.C. and P.O.C. flux to estimates of the energy budgets of stream ecosystems is discussed and published methods for the automatic measurement of D.O.C. are reviewed.     

The application of the Lymnaea stagnalis embryo-test in the toxicity bioindication of surfactants in fresh waters

The aim of this study was to assess the efficiency of the new acute toxicity bioassay with the application of embryological criteria, using aquatic invertebrates such as Lymnaea stagnalis L. We were looking for optimal methods of water bio-monitoring, comparing the sensitivity of different biotests. Different forms of snails (embryonic and juvenile) were tested and the tests compared to each other and to the daphnia (EN ISO 6341) test as well. The tested substances were surfactants, which are now regarded global threat to surface waters. The main source of detergent pollution is municipal and industrial wastewater. The tested groups were exposed to various concentrations of diluted surfactant agents known as Brij 32, Brij 58, Bri 72, Brij 76, Brij 78 and the detergent known under the trade name of Ludwik. The results proved that juvenile forms showed higher sensitivity to the tested toxicants. Therefore, they could be used as a potential tool to monitor the acute toxicity of surfactants, which could be presence in aquatic ecosystems.     

Measurements of photosynthesis and respiration in plants

Methods for measuring the rates of photosynthesis and respiration in plants are reviewed. Closed systems that involve manometric techniques, ¹⁴CO₂ fixation, O₂ electrodes and other methods for measuring dissolved and gas phase O₂ are described. These methods typically provide time-integrated rate measurements, and limitations to their use are discussed. Open gas exchange systems that use infra-red CO₂ gas analysers and differential O₂ analysers for measuring instantaneous rates of CO₂ and O₂ exchange are described. Important features of the analysers, design features of gas exchange systems, and sources of potential error are considered. The analysis of chlorophyll fluorescence parameters for estimating the quantum yield for O₂ evolution and CO₂ fixation is described in relation to new fluorescence imaging systems for large scale screening of photosynthetic phenotypes, and the microimaging of individual chloroplasts.     

The spectral absorption and scattering properties of dissolved and particulate components in relation to the underwater light field of some tropical Australian fresh waters

SUMMARY. 1. The inherent optical properties (scattering coefficients and absorption coefficients across the photosynthetic waveband) are presented from diverse tropical water bodies (billabongs) in the Alligator Rivers Region of northern Australia.
2. The data are used to interpret observed characteristics of the underwater light field as exemplified by the spectral distribution, and overall rate of attenuation, of photosynthetically available radiation (PAR).
3. Attenuation of PAR, especially in the blue waveband, is caused primarily by intense light absorption by the yellow-brown humic pigments, both soluble and particulate, in the water.
4. It was estimated that in six moderately turbid billabongs, light scattering increased attenuation by an average of 58% above that attributable to absorption alone, whereas in a highly turbid billabong the increase was 111%.
5. A distinguishing feature of the optical character of these billabongs, compared with previously studied water bodies in southern Australia, is the great contribution to light absorption made by the particulate humic material.     

The fresh waters of Shetland: Chemical characteristics of running waters

The water chemistry of 48 streams on Shetland was determined as part of a synoptic survey of the islands during 1974. Principal component analysis identified three main contributors to stream chemistry: solid geology, drift geology (in the form of peat) and marine influence. The sites could be clustered by their chemistry according to these factors. The likely chemical characteristics of sites could be predicted from map analysis of altitude, solid and drift geology and oceanicity. There was little evidence of acidification of Shetland streams, but the peatiness of the water made acidification difficult to detect using the usual criteria. Most sites did show a reduction in alkalinity compared to a calculated value for non-aidified sites.     

Introduction to optical methods in photosynthesis

Optical spectroscopy is widely used to study structure and function of photosynthetic systems. Due to the large variety of different methods, these studies have contributed a lot to the identification of the cofactors involved in the primary reactions of photosynthesis and to the elucidation of the kinetics of the light-induced energy and electron transfer reactions. Within other aspects of photosynthesis research as e.g. photoinhibition, these techniques play an important role as well. In this brief introduction, I will focus on the basic principles of the different methods and the information obtained by applying these various techniques. In the reviews that follow, under the section “Optical Methods”, these methods are discussed in detail.     

Community photosynthesis and respiration in experimental streams

Changes in relative contribution to total stream photosynthetic and respiratory rates by various community components of an open channel stream were estimated. Rates of photosynthetic production of plankton, benthos and macrophytes (with associated epiphytes) were followed through the growing season and compared with total estimates from a diurnal oxygen technique. Photosynthetic production by macrophytes was extremely high early in the growing season; but later declined and heterotrophic processes became predominant. In contrast, benthos production was initially low but became the primary source of photosynthesis later in the season. Plankton contributed little to stream photosynthesis and respiration.     

Variation in leaf respiration in relation to growth and photosynthesis of Lolium

Six Lolium genotypes with contrasting apparent photorespiration and CO_a compensation concentration, [C0₂]_c, were compared for net photosynthesis, dark respiration, leaf starch accumulation, rate of leaf expansion and shoot regrowth. Plants were grown in day/night temperatures of 15/10 and 25/20 ^oC. There were significant (P < 0–05) differences between the genotypes in all these parameters. At 25/20 ^oC apparent photorespiration was correlated with [CO₂]_c. Correlation coefficients, pooled from both temperature regimes, revealed that genotypes with high rates of net photosynthesis accumulated more leaf starch during light periods than genotypes with slow photosynthesis, but rates of leaf expansion and dry matter increase were only correlated, negatively, with dark respiration. Apparent photorespiration was negatively correlated with dark respiration. These findings suggest that attributes related to photorespiration such as [CO₂]_c and O₂ uptake from CO₂-free air in the light are unlikely to be useful selection criteria for growth of C₃ grasses, that net photosynthesis was probably not limiting growth and that maintenance respiration may have been an important determinant of genotypic differences in growth rate. Selections for slow and fast rates of dark respiration of mature leaves were therefore made at 8 and at 25 ^oC from within two different populations of L. perenne, S.23. This characteristic showed repeatabilities (broad-sense heritability) of from 0–41 to o-66. Six independent comparisons of simulated swards of the slow- and fast-respiring selections were made under periodic cutting regimes, either in a growth room at 25 ^oC or in a glasshouse from August to May. Growth of all plots of slow-respiring genotypes was consistently more rapid than that of the fast-respiring, at 25 ^oC in the growth room, and during autumn and spring in the glasshouse. There was no difference in winter growth. The implications of these results for the use of gas exchange measurements as selection criteria in plant breeding programmes are discussed.     

Methane oxidation coupled to oxygenic photosynthesis in anoxic waters

Freshwater lakes represent large methane sources that, in contrast to the Ocean, significantly contribute to non-anthropogenic methane emissions to the atmosphere. Particularly mixed lakes are major methane emitters, while permanently and seasonally stratified lakes with anoxic bottom waters are often characterized by strongly reduced methane emissions. The causes for this reduced methane flux from anoxic lake waters are not fully understood. Here we identified the microorganisms and processes responsible for the near complete consumption of methane in the anoxic waters of a permanently stratified lake, Lago di Cadagno. Interestingly, known anaerobic methanotrophs could not be detected in these waters. Instead, we found abundant gamma-proteobacterial aerobic methane-oxidizing bacteria active in the anoxic waters. In vitro incubations revealed that, among all the tested potential electron acceptors, only the addition of oxygen enhanced the rates of methane oxidation. An equally pronounced stimulation was also observed when the anoxic water samples were incubated in the light. Our combined results from molecular, biogeochemical and single-cell analyses indicate that methane removal at the anoxic chemocline of Lago di Cadagno is due to true aerobic oxidation of methane fuelled by in situ oxygen production by photosynthetic algae. A similar mechanism could be active in seasonally stratified lakes and marine basins such as the Black Sea, where light penetrates to the anoxic chemocline. Given the widespread occurrence of seasonally stratified anoxic lakes, aerobic methane oxidation coupled to oxygenic photosynthesis might have an important but so far neglected role in methane emissions from lakes.     

施氮处理下植物光合对沙质草地土壤呼吸的调控作用

本研究以科尔沁沙质草地为对象,探讨施氮对沙质草地土壤CO₂排放影响的光合调控机制.结果表明: 施氮可通过增加地上植物光合改变输送到地下的光合同化产物数量,进而对土壤呼吸速率产生调控作用.植物光合速率与土壤呼吸速率呈显著正相关,施氮后二者拟合函数斜率由0.236降至0.161,拟合方程截距差值(0.51 μmol·m^-2·s^-1)与施氮后夜间土壤呼吸速率提升值(0.52 μmol·m^-2·s^-1)相近.5—10月,施氮后光合速率改变值(比率)与土壤呼吸变化值(比率)呈显著正相关,偏相关分析显示,施氮后光合速率的改变值是影响土壤呼吸速率变化的有效解释因素(P<0.05).夜间土壤呼吸速率变化仍与地上植被活动存在重要联系,日均生态系统总光合是影响夜间土壤呼吸速率变化(ΔR_s)的重要因素(P<0.01).植物光合而非温度条件是影响施氮后土壤呼吸速率变化的主要因素,因而,结合植物光合的同化产物控制途径为施氮对土壤呼吸影响机制研究提供新的重要补充.     

The interaction of respiration and photosynthesis in induction of nitrate reductase activity

The respiration and photosynthesis requirement for induction and maintenance of nitrate reductase activity was determined on leaves of Hordeum vulgare L. In this induction, glucose substituted for light in both dark-grown and carbohydrate-depleted green leaves. Oxygen appeared to be required for induction in all cases studied. In light and under N₂, 3-(3,4-dichlorophenyl)-1,1-dimethylurea completely inhibited induction, presumably by inhibiting the production of O₂, Hence, under N₂ the leaves appeared to utilize both the O₂ produced by photosynthesis and the CO₂ produced by respiration. CO₂ fixation can then produce both photosynthate to drive the induction and terminal electron acceptors to allow photosynthetic electron flow. This possibility was further suggested by the observation that CO₂ was an absolute requirement for induction in carbohydrate-depleted barley leaves. Results obtained with respiratory inhibitors also indicated that respiration drove the induction of nitrate reductase.