A NEW MECHANISM FOR CALCIUM LOSS IN FOREST-FLOOR SOILS

CALCIUM is the fifth most abundant element in trees, and is an essenti al component for wood formation and the maintenance of cell walls. Dep letion of Ca from the rooting zone can result in acidification of soil (1) and surface water(2) and possibly growth decline and dieback of re d spruce(3,4). During the past six decades, concentrations of root-ava ilable Ca (exchangeable and acid-extractable forms) in forest-floor so ils have decreased in the northeastern United States(5,6). Both net fo rest growth and acid deposition have been put forth as mechanisms that can account for this Ca depletion(5,6). Here, however, we present dat a collected in red spruce forests in the northeastern United States th at are inconsistent with either of these mechanisms. We propose that a luminium, mobilized in the mineral soil by acid deposition, is transpo rted into the forest floor in a reactive form that reduces storage of Ca, and thus its availability for root uptake. This results in potenti al stress to trees and, by increasing the demand for Ca, also decrease s neutralization of drainage waters, thereby leading to acidification of lakes and streams.