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- Ekblad, Alf, 1957-, et al.
(författare)
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Day-to-day variation in nitrogenase activity of alnus-incana explained by weather variables : a multivariate time-series analysis
- 1994
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Ingår i: Plant, Cell and Environment. - : Wiley. - 0140-7791 .- 1365-3040. ; 17:3, s. 319-325
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Tidskriftsartikel (refereegranskat)abstract
- A modelling system is described that indicates the extent to which day-to-day variations in nitrogenase activity in young Alnus incana (L.) Moench, grown in defined conditions in the field, may be affected by weather conditions both during and prior to the day of measurement. Nitrogenase activity (acetylene reduction activity, ARA) was measured weekly on intact field-grown grey alder (A. incana) plants, 0.15–0.42 m tall at planting, nodulated with Frankia. The measurements were done at noon on two groups of plants in 1987 and on two other groups in 1988. Each group was made up of five or six plants. Seven weather variables: daily sunshine hours, daily mean, maximum and minimum air temperature, daily mean and 1300 h relative humidity, and daily rainfall were used. The relation between log(ARA/leaf area) and the weather variables were analysed using a PLS model (partial least squares projection to latent structures). The advantage of PLS is that it can handle x-variables that are correlated. Data from 1987 were chosen as a training set. Multivariate PLS time series analysis was made by adding, in a stepwise manner, the weather data up to 5 d before the day of measurement. This procedure gave six models with n * 7 x-variables (n= 1–6). With the models from the time series analysis of 1987 data, true predictions of ARA per leaf area were made from weather data 1988 (test set 1) and from ‘early-season’ weather data from 1987 and 1988 (test set 2). The variation in ARA/leaf area could be predicted from the weather conditions. The predictions of the two test sets improved when the weather conditions one and two days before the day of measurements were added to the model. The further addition of weather data from 3 to 5 d before the day of measurement did not improve the model. The good predictions of ARA/leaf area show that the alders responded to the variable weather conditions in the same way in 1988 as in 1987, despite the ten-fold difference in size (leaf area) at the end of the growing season. Among the weather variables, air temperature and the daily sunshine hours were positively correlated to ARA, while relative air humidity and rainfall were negatively correlated to ARA. The daily minimum temperature and rainfall appeared to have least impact on ARA. By use of PLS, we could extract information out of a data set containing highly correlated x-variables, information that is non-accessible with conventional statistical tools such as multiple regression. When making measurements of nitrogenase activities under field conditions, we propose that attention should be paid to the weather conditions on the days preceding the day of measurement. The day-to-day variation in nitrogenase activity is discussed with reference to known effects of stress factors under controlled conditions.
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| 2. |
- Larsson, Staffan, 1947-, et al.
(författare)
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Kortutbildade i kunskapsamhället
- 1991
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Ett forskningsprogram om forskning kring kortutbildades situation
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| 3. |
- Lundquist, Per
(författare)
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Determination of cyanide and thiocyanate in humans
- 1992
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cyanide exposure from several sources may cause chronic diseases or acute lethal intoxication in humans. Accurate and specific methods for determination of cyanide and its metabolite thiocyanate are therefore needed for clinical and epidemiological purposes. An improved method for determination of thiocyanate in serum and urine was developed by adsorption of thiocyanate on a weakly basic anion-exchange resin by a chaotropic effect, followed by colorimetrical determination by a modified Konig reaction. Dietary intake of cyanide and sulfur was estimated by determination of urinary thiocyanate and inorganic sulfate in a Mozambican population affected by the paralytic disease konzo. Konzo was found to be associated with a high cyanide and low sulfur intake from a diet dominated by cassava roots that were consumed without removal of the naturally occurring cyanogen compounds. A low intake of sulfur containing proteins was supposed to enhance toxic effects of cyanide by reducing cyanide to thiocyanate conversion.For determination of blood cyanide in field studies an analytical method that enabled transport of samples was developed. Cyanide was stabilized in blood by adding silver ions and after distillation determined by the Konig reaction. A 30-fold increase in sensitivity was obtained by fluorometric determination of the Konig chromogen, which enabled determination of physiological blood cyanide levels 0.117 ± 0.038 J..Ullol/L (mean± SD), and blood cyanide after smoking a cigarette 0.424 ± 0.173 f.tmol/L. A rapid method for determination of toxic blood cyanide levels could be developed by separating the cyanide containing erythrocytes from thiocyanate containing plasma by washing with saline and thereafter protein precipitation followed by direct spectrophotometric determination of the König chromogen.Measurement of hydrogen cyanide in breath showed no correlation with blood levels of cyanide. Experiments revealed that most of the hydrogen cyanide found in breath from normal human beings originates from oxidation of thiocyanate by salivary peroxidase in the oropharynx.In a study of fire casualties 9 out of 18 victims had toxic blood cyanide levels (> 40 J..Ullol/L) and one had a blood cyanide level of 101 J..UllOI/L but a nontoxic blood carboxyhemoglobin, which suggests a lethal effect of cyanide exposure. Blood cyanide levels in two suicidal intoxications were found to be 105 and 139 J..UllOl/L. A lethal outcome in one of the cases that received insufficient antidotal treatment indicates that immediate laboratory verification of cyanide intoxication may be life-saving.
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