A low cost instrument for measurement of photosynthetically active radiation in field canopies

A robust, relatively low cost (parts $300 Aust., 1976) instrument suitable for field studies was constructed to give rapid estimates of photosynthetically active radiation, both absolute and as percentage transmission, within plant canopies. The instrument consists of 9 selenium photocells mounted in a probe and a single selenium cell as the reference sensor. The performance of the instrument was evaluated in both the laboratory and field

The determination of native ionic copper concentrations and copper complexation in peat soil extracts

In acid peaty soils most of the copper in the soil solution is present as organic complexes. This paper describes methods for measuring total soil solution copper by flameless atomic absorption spectroscopy and estimating the proportion of this copper that is complexed using copper titration and a copper ion selective electrode. With these acidic peats of diverse origin, total copper in solution at natural pH values (3.4 to 3.5) ranged from 0.14 to 0.2 μM. of this, 60 to 90% was complexed. Raising the pH of aqueous extracts to about 6.0 increased the degree of complexation of soluble copper in extracts of all three peats to >98%. We discuss the results in relation to current thinking about the nature of copper complexation by humic and fulvic acids

Release characteristics of ion-exchange resins as buffers in low ionic strength nutrient solutions

The use of synthetic ion-exchange resins as buffers of nutrient ions is a potential mechanism for the control of ion concentrations in nutrient solutions. In this study equilibrium constants for two cation exchange resins and three anion exchange resins were determined at 25°C in low ionic strength systems. The measured constants were used to successfully predict the resin combinations required to achieve desired solution equilibrium concentrations. The effectiveness of these resins in buffering solution ion concentrations was evaluated by examining their release characteristics in circulating systems from which aliquots of solution were withdrawn and replaced with deionised water to simulate plant uptake. Buffering of NO3 and SO4 concentrations was effective when manual control of one anion was imposed. The cation resins were ineffective in buffering the concentrations of Ca and Mg with a tendency for the resins to retain most of the Ca and Mg in adsorbed form

Chloride determination in plant tissue using a solid state chloride ion specific electrode

A solid state Ion Specific Electrode was evaluated for direct determination of chloride in extracts of oven dried, ground plant material. When samples were extracted with water, the electrode response was slow and there was a tendency to overestimate tissue chloride concentrations. When extracted with 0.5 M HNO3 the response time was fast and the recovery of added chloride close to 100 percent. The method developed is simple, rapid, and accurate

The determination of dissolved organic carbon by inductively coupled plasma atomic emission spectroscopy

Dissolved organic carbon (DOC) present in soil solutions was measured by inductively coupled plasma atomic emission spectroscopy (ICPAES) using the two C(I) lines at 197.09 nm and 247.856 nm. Carbon standards, prepared from sucrose, in the range 100 to 1000 mg L-1 produced linear coefficients of determination of r2 ≥ 0.9998 for each of the lines with calculated detection limits of 0.034 and 1.094 mg L-1 for each line, respectively. Inorganic carbon was eliminated from solution by the addition of concentrated nitric acid and sparging with high purity nitrogen for 30 min. A comparison of the DOC values for soil solutions extracted from nine soil samples by ICPAES and dichromate oxidation showed a high degree of correlation ( r2 ≥ 0.9982). Copyrigh

Determination of total soluble aluminum in soil solution using pyrocatechol violet, lanthanum and iron to discriminate against micro-particulates and organic ligands

The determination of the Al concentration in soil solution is an important diagnostic tool in studies of Al toxicity in acid soils. Where organic residues have been applied as améliorants of Al toxicity, it is necessary to measure both the total soluble and monomeric Al concentrations in order to estimate the degree of Al complexation. Determination by ICPAES provides a measure of total Al without discrimination between chemical forms, and thus may include solid-phase Al present as micro-particulates that have passed through a 0.22 pm filter. Colorimetric methods, which do not include an acidification step, discriminate against micro-particulates, but do not measure all Al present as soluble organic forms and thus underestimate total soluble Al. Acidification of soil solutions to decomplex organically bound Al, and thus permit its measurement by colorimetric methods, results in dissolution of micro-particulates and overestimation of total soluble Al. Filtering to 0.025 pm eliminated microparticulates, thereby removing a source of error. However, this process is time consuming and thus unsuitable for routine use

In vitro evidence of aluminum effects on solution movement through root cell walls

Little is known about the primary effects of aluminum (Al) in reducing root growth. However, the sorption of Al by the root cell wall, particularly by calcium (Ca) pectate, has been suggested as being important in the expression of Al toxicity in plants. To overcome problems arising from the close proximity of root cell components that may react with Al, a synthetic Ca pectate membrane was prepared as a model system for Al studies. Solution containing 1 mM Ca (as CaCl2) was passed through the membrane, and the flow rate measured. Solution containing 29 μM Al (as A1C13) and 1 mM Ca reduced solution flow rate by > 80% from c. 3.5 to c. 0.6 mL/min within 2 min, with a further slight decline over the next 4 min. The Al concentration in solution proximate to the inlet side of the membrane decreased to 15 μM within 10 min, and only 3 μM Al was measured in solution that had passed through the membrane. These results suggest that an important primary effect of toxic Al is a reduction in water movement into the root, with consequent effects on water relations in the plant

A semimicro apparatus for essential oil determination of multiple mint samples by steam distillation

An apparatus is described which allows simultaneous steam distillation of ten individual plants for essential oil determination. Volume of recovered oil can be read to 0.01 mL. Tests on mint oil for accuracy and reproducibility gave a mean recovery of 89.9 ± 1.1%. Yields of oil from plant of five species and varieties of mint (Mentha) ranged from 3.45 to 8.90%

Effects of organic acid fractions extracted from Eucalyptus camaldulensis leaves on root elongation of maize (Zea mays) in the presence and absence of aluminium

Complexes of aluminium (Al) with organic ligands are believed to represent an important detoxification mechanism in acid soils. However, relatively little is known about the particular ligands produced by decomposing vegetation or about their effects on plant growth in the presence or absence of toxic Al. This paper reports an experiment on the effects of decomposition products of Eucalyptus camaldulensis leaves on the root elongation of maize (Zea mays) cv. DK687 in the presence or absence of Al. The static solution culture experiment used fulvic acid (FA) and humic acid (HA), extracted from E. camaldulensis leaves, at three nominal concentrations, viz. 40, 120 and 360 mg C L-1, replicated 4 times in the presence and absence of 30 μM Al. In the absence of Al, root elongation was increased by 30% by HA at 40 mg C L-1 and by 36% by FA at 120 mg C L-1. In the presence of 30 μM Al, the effects of toxic Al on root elongation were negated by FA and HA at all concentrations. Aluminium was totally complexed in all treatments except FA at 40 mg C L-1 in which treatment only 2.7 μM Al was present in the monomeric form. The E. camaldulensis FA and HA at concentrations of 40 and 120 mg C L-1, either in the presence or absence of Al, stimulated maize root elongation. Aluminium was strongly complexed by the E. camaldulensis FA and HA. The present results, in which FA and HA alleviated Al toxicity limitations on root elongation of maize, are relevant to the protection afforded to plant growth in acid soils amended with organic materials. They highlight the need to focus more on the role of FA and HA