Foliar response of red spruce saplings to fertilization with Ca and Mg in the Great Smoky Mountains National Park

The objective of this field study was to test whether Ca and (or) Mg was deficient in two red spruce (Picearubens Sarg.) sites located at 1720 and 1950 m in elevation in the Great Smoky Mountains National Park near Clingmans Dome, North Carolina. Initial current needle Ca and Mg concentrations were, respectively, 1700 and 620 μg/g at the upper site, and 1940 and 670 μg/g at the lower site, suggesting poorer nutrient conditions at the upper site. Twenty-eight saplings at each site stratified by height were involved in an individual-tree fertilization trial. Within each stratum four treatments were applied randomly: (i) no fertilization, (ii) 200 kg/ha Ca as CaCl2, (iii) 100 kg/ha Mg as MgCl2, and (iv) 200 kg/ha Ca as CaCl2 plus 100 kg/ha Mg as MgCl2. Fertilizer was applied in April 1989 and 1990, and needles that subsequently formed in the 1989 and 1990 growing seasons were sampled in November 1989 and 1990, respectively. Post-fertilization nutrient concentrations, needle weights, and nutrient contents were compared through analysis of covariance with the pre-treatment needle weight as covariate. Vector analysis suggested an improvement in Ca nutrition and potential growth response with Ca and Ca + Mg fertilization at the upper site in the 1st year but not at the lower site. Neither site appeared to be Mg deficient. Magnesium fertilization had an antagonistic effect on Ca uptake at both sites, whereas Ca addition seemed to improve Mg uptake. Our study suggests that foliar Mg concentrations of 600 μg/g are well within the sufficiency range, but that red spruce saplings may experience incipient Ca deficiency in the field when Ca concentrations in the current needles are <1700 μg/g.