ABSTRACT
Sodium is unique among abundant elemental nutrients, because most plant species do not require it for growth or development, whereas animals physiologically require sodium. Foliar sodium influences consumption rates by animals and can structure herbivores across landscapes. We quantified foliar sodium in 201 locally abundant, herbaceous species representing 32 families and, at 26 sites on four continents, experimentally manipulated vertebrate herbivores and elemental nutrients to determine their effect on foliar sodium. Foliar sodium varied taxonomically and geographically, spanning five orders of magnitude. Site-level foliar sodium increased most strongly with site aridity and soil sodium; nutrient addition weakened the relationship between aridity and mean foliar sodium. Within sites, high sodium plants declined in abundance with fertilisation, whereas low sodium plants increased. Herbivory provided an explanation: herbivores selectively reduced high nutrient, high sodium plants. Thus, interactions among climate, nutrients and the resulting nutritional value for herbivores determine foliar sodium biogeography in herbaceous-dominated systems.
Subject(s)
Grassland , Herbivory , Sodium , Adaptation, Physiological , Animals , Nitrogen , Plants , SoilABSTRACT
We describe a continuous-flow, automated determination of total cholesterol in serum, which is based on enzymatic hydrolysis of cholesterol esters, oxidation of cholesterol by cholesterol oxidase, and colorimetric measurement of liberated perioxide with 4-aminoantipyrine, phenol, and peroxidase. Free cholesterol is determined with the same AutoAnalyzer II manifold and reagents, except that cholesterol esterase is omitted from the reagent. Cholesterol-in-serum materials that have been assayed by an established method are used for calibration. We found this approach to be necessary because primary cholesterol standards in organic solvents are incompatible with the aqueous reagent. Results of the enzymatic total cholesterol method correlated well with those by an AutoAnalyzer II method which involves an extraction with isopropanol and the Liebermann-Burchard color reaction (total cholesterol, g/liter, yenz= 0991xlb +0.05;r=0.996). Results of the enzymatic free cholesterol procedure agreed satisfactorily with one in which free cholesterol is precipitated as the digitonide and subsequently analyzed colorimetrically with the Liebermann-Burchard reaction (free cholesterol, %, yenz = 0.982xdig -0.7;r= 0.956).
Subject(s)
Cholesterol Esters/blood , Cholesterol/analogs & derivatives , Cholesterol/blood , Hydroxysteroid Dehydrogenases , Autoanalysis , Colorimetry/methods , Humans , Indicators and Reagents , MethodsABSTRACT
We describe an enzymatic method, requiring only 10 mul of serum, for determining CO2 as bicarbonate or dissolved gas. Phosphoenolpyruvate carboxylase catalyzes the reaction of HCO3- with phosphoenolypyruvate to give oxalacetate. The resulting NADH, in the presence of malate dehydrogenase, is oxidized to NAD+, and the decrease in absorbance at 340 nm is directly proportional to the amount of CO2 present in the sample. Reaction is complete in 3 to 6 min under assay conditions, and is linearly related to CO2 concentrations between 8 and 65 mmol/liter. Analytical recovery is 95-110% (average, 101%). Two laboratories compared values obtained by continuous-flow analysis. The resulting correlation coefficients were 0.966 and 0.987, values for the t-test were t(paired) equals 0.473 and t(paired) equals 0.334, and average day-to-day precisions (three concentrations) were 3.9% and 4.2%.
