FOLIAR CATION CONTENTS OF LAUREL FOREST TREES ON THE CANARY-ISLANDS

The leaf cation contents of 15 different tree species of the laurel fo rest on the Canary Islands were measured. Different developmental stag es of leaves were compared to estimate the effect of leaf age on the c ation content. Young expanding leaves showed quite high potassium valu es when compared with mature leaves from the previous year and with se nescing leaves. The opposite trend, accumulation with age, generally o ccurred with Ca, Mg, Fe, Mn, and Al, but with species-specific intensi ty. The levels of the investigated elements varied considerably betwee n the species; exceptionally high nutrient levels were found in Viburn um rigidum. The cations in the leaves from laurel forest trees were si milar to the reported ion contents in leaves of tropical trees, both b eing higher than those in leaves of temperate forest trees. In most sp ecies of the laurel forest the aluminium contents were between 10 and 30 mmol kg(-1) dw. This was far above the Al contents of most other te rrestrial plants and pointed to a high Al availability in the soils an d a high foliar Al tolerance. Accumulation of Al - and to a lesser ext ent Fe and Mn as well - could be considered a consequence of primitive traits of the coriaceous leaf type like longevity and poor transpirat ion control.