X-ray Microanalysis of Needles from Douglas Fir Growing in Environments of Contrasting Acidity

Douglas fir Pseudotsuga menziesii (Mirb.) Franco] shoots from mature trees were collected from two sites of contrasting soil pH: the Glendon campus of York University in Toronto, Canada (pH 6.7 at 40 cm) designated Can.; and Breuil Forest, Morvan, France (pH 4 to 4.5) designated Fr.. Needles were removed from the shoots, frozen in liquid nitrogen, and kept in a cryo-biological storage system prior to X-ray microanalysis on the cold stage (−170°C) of a cryo-SEM. Four elements detected, potassium, phosphorus, sulphur and chlorine, were ubiquitous in the needle tissues from both sites. Manganese was infrequently found in needle tissues from the Fr. site. Calcium was localized most heavily in the outer tangential wall of the hypodermis and also in the epidermal walls. Silicon (Si) concentrations were higher in the Fr. site than in the Can. site. The epidermis, hypodermis and mesophyll of needles from the Fr. site exhibited the highest Si content, with greater amounts in the tip and middle of the needle than in the base. Aluminium was distributed fairly evenly throughout the tissues, and there were few major sites of concentration.