Forest fire: effects on phosphorus movement to lakes.

After a wildfire in the virgin forest of a lake-watershed region in northeastern Minnesota, the phosphorus concentration in the runoff was elevated for 2 years and decreased in the third year. However, there was no increase in the phosphorus concentrations of a lake and its input stream. This indicates that, under similar circumstances, controlled burning will not damage streams or lakes by elevating phosphorus levels.

Soil and litter phosphorus-31 nuclear magnetic resonance spectroscopy: extractants, metals, and phosphorus relaxation times.

Phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy is an excellent tool with which to study soil organic P, allowing quantitative, comparative analysis of P forms. However, for 31P NMR to be tative, all peaks must be completely visible, and in their correct relative proportions. There must be no line broadening, and adequate delay times must be used to avoid saturation of peaks. The objective of this study was to examine the effects of extractants on delay times and peak saturation. Two samples (a forest litter and a mineral soil sample) and three extractants (0.25 M NaOH, NaOH plus Chelex (Bio-Rad Laboratories, Hercules, CA), and NaOH plus EDTA) were used to determine the differences in the concentration of P and cations solubilized by each extractant, and to measure spin-lattice (T1) relaxation times of P peaks in each extract. For both soil and litter, NaOH-Chelex extracted the lowest concentrations of P. For the litter sample, T1 values were short for all extractants due to the high Fe concentration remaining after extraction. For the soil sample, there were noticeable differences among the extractants. The NaOH-Chelex sample had less Fe and Mn remaining in solution after extraction than the other extractants, and the longest delay times used in the study, 6.4 s, were not long enough for quantitative analysis. Delay times of 1.5 to 2 s for the NaOH and NaOH-EDTA were adequate. Line broadening was highest in the NaOH extracts, which had the highest concentration of Fe. On the basis of these results, recommendations for future analyses of soil and litter samples by solution 31P NMR spectroscopy include: careful selection of an extractant; measurement of paramagnetic ions extracted with P; use of appropriate delay times and the minimum number of scans; and measurement of T1 values whenever possible.

Relationships between Some Nutritional Factors and the Distributions of Eucalyptus Gummifera and Eucalyptus Maculata.

The sharply delimited distributions of Eucalpytus gummifera and Eucalyptus maculata on the south coast of New South Wales were not statistically correlated with differences in physical and chemical properties of the supporting soils. Slight trends suggest that E. gummifera soils are not different physical quality and of lower nutrient status than E. maculata soils. Pot trials of interspecific competition for soil nutrients were inconclusive. Long-term field trials are recommended in which interspecific competition for other factors is also encountered. Chemical analyses and a pot trial indicated low concentrations of nitrogen, phosphorus, and calcium in some soils of the study area. Pot trails suggest that E. gummifera seedlings require less soil nitrogen and calcium than do E. maculata seedlings. Correlations are significant at the 0.05 level between phosphorus and calcium concentrations in plant tissues and the corresponding concentrations in supporting in supporting soils. The two species appear to differ in their ability to take up, and perhaps their requirement for soil phosphorus, calcium, nitrogen, and possibly manganese.

Mass-Action Expressions of Ion Exchange Applied to Ca, H, K, and Mg Sorption on Isolated Cells Walls of Leaves from Brassica oleracea.

The cation exchange properties of cell walls isolated from collard (Bassica oleracea var acephala D.C.) leaves were investigated. Cation sorption on cell walls was described by mass-action expressions of ion exchange, rather than by the traditional Donnan equilibrium. The mass-action expressions enable the selectivity of the wall for one cation over another to be determined unambiguously from ion exchange isotherms. We found that: (a) the cation composition of the wall varied as a function of the solution cation concentration, solution cation composition, and pH in a way predicted by mass action; (b) the affinity of the wall for divalent cations increased as the equivalent fraction of divalent cation on the wall increased, and as the concentration of divalent cations in solution increased; (c) the selectivity of the wall for any metal cation pair was not altered by the concentration of H(+) in solution or on the wall; (d) H(+) sorption on the wall may be treated as a cation exchange reaction making it possible to calculate the relative affinity of the wall for metal cation pairs from H(+)-metal (Me) titration curves; and (e) the relative affinity of the wall for the cations we studied was: H(+) >> (K(+) >/= Ca(2+)) > Mg(2+). A cation-exchange model including surface complexes is consistent with observed cation selectivity. We conclude that metal cations interact with the wall to minimize or eliminate long-range electrostatic interactions and suggest that this may be due to the formation of site-specific cation-wall surface complexes.

Fungal toxicity of mobilized soil aluminum and manganese.

Inhibition of Aspergillus flavus growth from spores was used as a simple bioassay for toxicity of Al and Mn mobilized by simulated acid precipitation. Al was identified as being toxic in soil leachates resulting from acid inputs of pH less than 2.7. Inhibition by Mn was not detectable. The addition of fluoride significantly reduced Al toxicity, suggesting that biotoxicity of Al is partially dependent on the anionic composition of the soil solution.