Abstract. Past use of lead arsenate insecticides has resulted in elevated concentrations of lead (Pb) and arsenic (As) in topsoils of many existing and former deciduous tree fruit orchard sites throughout the world. Application of phosphate (PO4)-containing fertilizers to these soils can increase soil As solubility, phytoavailability and downward mobility. A laboratory soil column experiment was conducted to determine if As released by phosphate additions to a topsoil artificially contaminated with lead arsenate (1.65 mmol total Pb/kg; 1.10 mmol total As/kg) would be appreciably resorbed by the underlying uncontaminated subsoil. Treatments were a factorial combination of topsoil amendment with monoammonium phosphate (MAP, 0 or 16.67 mmol POjkg), and amount of leaching ( 1, 5 and I0 pore volume displacements (PVD) with distilled water under saturated flow conditions). Soil As decreased in the topsoil with increasing amount of leaching and increased in the subsoil. Addition of MAP substantially increased loss of topsoil As, promoted As transport into and through the subsoil, and increased dissolved As concentrations in the column leachates. After 10 PVDs, 95% of the initial soil As remained in the -MAP columns, while 56% of the initial soil As remained the +MAP columns. Dissolved Pb concentrations were <0.05 itmol/L in all column leachates. The data are consistent with a mechanism of PO4-enhanced release of As in the topsoil and subsequent promotion of As movement through the subsoil by continuing competition of dissolved As and PO4 for ion adsorption sites. The experimental results indicate that use of PO4-containing fertilizers on lead arsenate-contaminated soils has the potential to greatly enhance downward movement of soil As.

Differential thermal analyses, 2,3,5-triphenyltetrazolium chloride stain, electrical conductance, and whole tree freezing test measurements were performed on ‘Golden Delicious’ apple (Malus domestica Borkh.) to monitor annual variations in cold resistance and compare test responses. A distinct pattern of exotherms was observed by thermal analyses throughout the year. The first exotherm at −6 to −9 °C represented the extracellular water. The second and third exotherms varied with the time of year and were at −10 to −39 °C, representing pith cells and xylem tissue, respectively. The lowest temperature exotherm occurred at −35 to −40 °C. Tetrazolium tests, performed at temperatures corresponding to each exotherm, showed that the cell damage occurred in the shoot interior and spread radially outward, with the secondary xylem being the most cold resistant. Comparison of electrical conductance with the xylem exotherm showed a nonlinear relationship. Stress tests on trees under controlled conditions showed that the temperature at the xylem exotherm was critical to the survival of the tree. Both the tetrazolium test and tree stress tests indicated that the lowest temperature exotherm could not be used as a measure of cold resistance. The possibility that thermal analysis is an improved measure of cold resistance is discussed.

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