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 Experimental 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 evaluate the influence of foliar nutrient content, precipitation amount, dry deposition, precipitation acidity and precipitation solute concentrations on throughfall chemistry. Calcium additions increased Ca foliar contents significantly. Foliar contents indicated plant uptake of Cl. Leaching of Cl from the canopy increased with elevated Cl content of the green foliage. Leaching rates for Ca, Mg, and K were not significantly different between the treatments (surprisingly Ca leaching tended to decrease with increasing foliar Ca content). We suggest that Ca supply to Ca deficient sugar maple trees protected the foliage from increased leaching of Ca (and other elements) due to improved integrity of cell membrane and cell wall formation from Ca. Degradation of the structural material of the foliage (autumnal leaf senescence, damages by ice and hail storms) caused Ca throughfall fluxes in accordance to measured foliar Ca contents. Increasing acidity of precipitation caused increased leaching of Ca, Mg and K. About half of the cation leaching from these sugar maple canopies is attributable to a cation-exchange reaction driven almost entirely-by H+ in precipitation. (C) 2001 Elsevier Science B.V. All rights reserved.