Mineral deposition in the needles of white spruce [Picea glauca (Moench.) Voss]

Abstract

Shoots from mature trees of white spruce [Picea glauca (Moench.) Voss] were collected in May 1994 from two sites of contrasting soil pH in the Great Lakes region of Central Canada: the Glendon campus of York University in Toronto, Ontario (pH 6.7 at 40 cm); and a site in the Muskoka-Haliburton Highlands near Huntsville, Ontario (pH 4.2 at 40 cm). Needles of ages 0-5 years were removed from the shoots. Percentage ash and percentage silica were determined in all age classes. Other needles were frozen in liquid nitrogen and stored in a cryo-biological storage system prior to x-ray microanalysis. The percentages of ash and silica increased with needle age in plants from both sites. Ash was higher in the Toronto samples than in the Muskoka samples, and percentage silica was higher in the Muskoka needles than in the Toronto samples. Of the eleven elements [magnesium (Mg), aluminium (Al), silicon (Si), phosphorus (P), sulphur (S), chlorine (Cl), potassium (K), calcium (Ca), manganese (Mg), copper (Cu) and zinc (Zn)] detected by microanalysis (mostly in cell walls), Mn, Cu and Zn were detected in minute amounts in internal tissues only, and P and S were almost ubiquitous in distribution. Magnesium concentrations were highest in the endodermis, and were higher in the endodermal outer tangential wall of the Muskoka needles than in the Toronto needles. Muskoka needles had higher K levels than Toronto needles; K accumulated in the endodermis and tended to decrease in older needles. Calcium was deposited mostly in the mesophyll and epidermis of the needles, increased with needle age, and was present at higher concentrations in the Toronto needles. Silicon was present in greater amounts in the needles from the Muskoka site, increased considerably in concentration with needle age, and was mainly located in the hypodermis, with lesser amounts in the epidermis, mesophyll and endodermal walls. Aluminium was confined to the needle epidermis.