Biomineralisation/environment interactions in conifers: Illustrated by hemlock, Tsuga canadensis (L.) Carr.

Eastern hemlock [Tsuga canadensis (L.) Carr.] shoots from mature trees were collected from two sites of contrasting pH in the mixed conifer–hardwood forest: the campus of York University in Toronto, Ontario (pH 6.6 at 3 cm) and the Muskoka region near Huntsville, Ontario, Canada (pH 4.0 at 3 cm). Needles of ages 1–3 years were stored in a cryo-biological unit at the temperature of liquid nitrogen prior to EDX microanalysis. Of the nine elements (Mg, Al, Si, P, S, Cl, K, Ca and Mn) detected by microanalysis, S, P, Cl and K were almost ubiquitous in distribution, while Mg was concentrated in the endodermal cells. Manganese was present at low levels in most tissues of needles from the acidic Muskoka site. Biomineralisation data, represented by Si, Ca and Al, were obtained for six leaf tissues. At both collection sites, Si and Ca content increased with needle age and in the 3 yr cohort, Si increased lengthwise towards the tip region. The epidermis, hypodermis and mesophyll tissues represented the major Ca sinks. At both sites, the highest Si readings in the older cohorts occurred in the xylem and transfusion tracheids followed by the hypodermis, mesophyll and endodermal walls, reaching maximal values in the needle tips. The highest Al localisation was coincident with that for Si at the tips of the 3 yr cohort.