Effects of calcium and aluminum chloride additions on foliar and throughfall chemistry in sugar maples

Calcium availability for sugar maple stands at the Hubbard Brook Experiment al Forest (New Hampshire, USA) was tested by experimental addition of CaCl2 and AlCl3. Additions of 10 g Ca m(-2) represented the estimated loss from the soil exchange complex during the last 30 years due to acidic deposition . Four years of data from 12 throughfall collection sites were used to eval uate the influence of foliar nutrient content, precipitation amount, dry de position, precipitation acidity and precipitation solute concentrations on throughfall chemistry. Calcium additions increased Ca foliar contents signi ficantly. Foliar contents indicated plant uptake of Cl. Leaching of Cl from the canopy increased with elevated Cl content of the green foliage. Leachi ng rates for Ca, Mg, and K were not significantly different between the tre atments (surprisingly Ca leaching tended to decrease with increasing foliar Ca content). We suggest that Ca supply to Ca deficient sugar maple trees p rotected the foliage from increased leaching of Ca (and other elements) due to improved integrity of cell membrane and cell wall formation from Ca. De gradation of the structural material of the foliage (autumnal leaf senescen ce, damages by ice and hail storms) caused Ca throughfall fluxes in accorda nce to measured foliar Ca contents. Increasing acidity of precipitation cau sed increased leaching of Ca, Mg and K. About half of the cation leaching f rom these sugar maple canopies is attributable to a cation-exchange reactio n driven almost entirely-by H+ in precipitation. (C) 2001 Elsevier Science B.V. All rights reserved.