Influence of plant nutrient concentration on growth rate: Use of a nutrient interruption technique to determine critical concentrations of N,P and K in young plants

A method is described for determining the way in which growth rate varies with plant nutrient concentration using a simple nutrient interruption technique incorporating only 2 treatments. The method involves measuring the changes in growth and nutrient composition of otherwise well-nourished plants after the supply of one particular nutrient has been withheld. Critical concentrations are estimated from the relationship between the growth rate (expressed as a fraction of that for control plants of the same size which remained well-nourished throughout) and the concentration of the growth-limiting nutrient in the plants as deficiency developed. Trials of the method using young lettuce plants showed that shoot growth rate was directly proportional to total N (nitrate plus organic N) concentration, and linearly or near-linearly related to K and P concentration over a wide range; the corresponding relationship for nitrate was strongly curvi-linear. Critical concentrations (corresponding to a 10% reduction in growth rate) determined from these results were similar to critical values calculated from models derived from field data, but were generally higher than published estimates of critical concentration (based on reductions in shoot weight) for plants of a similar size. Reasons for these discrepancies are discussed. Nitrate, phosphate or potassium concentrations in sap from individual leaf petioles were highly sensitive to changes in shoot growth rate as deficiency developed, with the slope of the relationships varying with leaf position, due to differences both in their initial concentration and in the rates at which they were utilized in individual leaves. Each nutrient was always depleted more quickly in younger leaves than in older ones, providing earlier evidence of deficiency for diagnostic purposes. Although the plants were capable of accumulating nitrate, phosphate and potassium well in excess of that needed for optimum dry matter production during periods of adequate supply, the rate of mobilization of these reserves was insufficient to prevent reductions in growth rate as the plants became deficient. This brings into question the validity of the conventional concept that luxury consumption provides a store of nutrients which are freely available for use in times of shortage. The implications of these results for the use of plant analysis for assessing plant nutrient status are discussed.     

Critical,pupal and adult weights in the size related metamorphosis of the black lyre leafroller ‘Cnephasia’ jactatana

Adult reproductive performance is linked to the period of feeding done by the final instar larva after attainment of a larval critical weight (L_CW). The highest weight attained by a final instar larva is referred to as the larval maximum weight (L_MW) and is the onset of the pre-pupal period. The relationships between L_CW, pupal weight (P_W) and adult weight (A_W) are described as functions of the L_MW. In the leafroller Cnephasia jactatana (Walker) (Lepidoptera: Tortricidae) L_CW was dependent on larval size and was approximately 75% of the mean L_MW. L_CW was about 29 mg and 36 mg for male and female larvae of 1.18 mm and 1.20 mm head-capsule width, respectively. Over three successive generations of laboratory rearing, P_W was approximately 30% and 25% lower than the L_MW for males and females, respectively. A_W was consistently about 50% and 40% lower than the P_W for males and females, respectively. The decrease in weight from L_MW to P_W was named as the constant D_P and found to be 0.3 for males and 0.25 for females. The total decrease from L_MW to A_W was the constant D_A and was 0.6 for males and 0.5 for females. The duration of the latent feeding period was positively correlated to P_W and A_W. L_CW may be used to derive quality indices that describe and predict pupal and adult performance.

---

Résumé Les performances reproductives sont liées à la période d'alimentation du dernier stade larvaire après l'obtention d'un poids critique (L_CW). Le poids maximal atteint au dernier stade larvaire est défini comme le poids larvaire maximal (L_MW), il correspond au début de la période prénymphale. Les relations entre poids de la chrysalide (P_W) et poids de l'audulte A_W) sont présentées comme des fonctions de L_MW). Chez Cnephasia jactatana Walker (Lep. Tortricidae), L_CW dépend de la taille de la chenille et correspond à environ 75% de la valeur moyenne de L_MW. L_CW est respectivement de 29 mg et 36 mg pour les chenilles mâles et femelles dont les capsules céphaliques ont 1,18 et 1,20 mm. Pour 3 générations successives, P_W est environ 30% et 25% inférieur à L_MW des mâles et des femelles. La régression du poids de L_MW à P_W est désignée comme la constante D_P et vaut 0,3 pour les mâles et 0,25 pour les femelles. La régression de L_MW à A_W est désignée comme la régression D_M et vaut 0,6 pour les mâles et 0,5 pour les femelles. La durée de la période d'alimentation latente est liée positivement à P_W et A_W. L_CW peut être utilisé comme indice dérivé décrivant et prédisant les potentialités nymphales et imaginales.

     

Thermal acclimation and hardening in tadpoles of the bullfrog, Rana catesbeiana

1. 1.|Critical thermal maxima (CTMax) and minima (CTMin) were measured to evalute thermal hardening in Rana catesbeiana.

2. 2.|Tadpoles show heat hardening and CTMax acclimation, and both responses are influenced by developmental stage.

3. 3.|The first evidence of cold hardening in vertebrates is reported here.

4. 4.|Heat hardening significantly reduces cold tolerance, but there is otherwise no evidence of a cross-hardening effect.

Rate of acclimation of the tropical salt-marsh fish Cyprinodon dearborni to temperature changes

The acclimation rates of temperature changes in Cyprinodon dearborni, collected from Laguna Los Patos, Cumana, Venezuela, were determined by the critical thermal maximum method. At an increase in temperature (from 24 to 31°C) fish started to gain acclimation level after 3 hours and took 3 days to fully get up to a higher level of resistance to heat death; however, at a decrease in temperature (from 3 t to 24°C) fish began to lose its acclimation level after 12 days and required 39 days to reach a lower level of resistance to thermal death.     

Critical threshold meal size and molt initiation in Rhodnius prolixus

The molting process and body growth in Rhodnius prolixus (Hemiptera: Reduviidae) (Ståhl, 1859) are significantly influenced by the availability and quality of food. Based on the body weight of each stage, the present study provides estimates of a potential critical weight threshold required for molt initiation in R. prolixus. In addition, a new measure given by the area under the weight curve is proposed, which encapsulates both body weight and time. It is shown that this measure is consistent with the data, and allows the estimation of a pre‐refractory period (i.e. the time interval between the moment at which the critical weight threshold is reached and the moment when no further meals are accepted). The present analysis estimates the critical weight threshold as 1.6, 5.3, 12.9, 42.0 and 97.0 mg for stages 1–5, respectively, whereas the values of the area under the curve threshold as 5, 16, 31.2, 159.7 and 329.9 mg days for stages 1–5, respectively. The results of the present study confirm the existence of a weight‐dependent mechanism for the initiation of molting in R. prolixus.     

Alcohol dehydrogenase-coupled spectrophotometric assay of plasmalogenase

Plasmalogenase has been assayed by conversion of the fatty aldehydes, released by hydrolysis of the vinyl ether bond of plasmalogens, to long-chain alcohols by horse liver alcohol dehydrogenase. The reaction was followed spectrophotometrically by measuring the oxidation of NADH. The assay is sufficiently sensitive to enable plasmalogenase activity to be determined in isolated oligodendroglia and derived membranes and in brain microsomal membranes using 50-250 micrograms protein.     

How to Report Record Open‐Circuit Voltages in Lead‐Halide Perovskite Solar Cells

Open‐circuit voltages of lead‐halide perovskite solar cells are improving rapidly and are approaching the thermodynamic limit. Since many different perovskite compositions with different bandgap energies are actively being investigated, it is not straightforward to compare the open‐circuit voltages between these devices as long as a consistent method of referencing is missing. For the purpose of comparing open‐circuit voltages and identifying outstanding values, it is imperative to use a unique, generally accepted way of calculating the thermodynamic limit, which is currently not the case. Here a meta‐analysis of methods to determine the bandgap and a radiative limit for open‐circuit voltage is presented. The differences between the methods are analyzed and an easily applicable approach based on the solar cell quantum efficiency as a general reference is proposed.