Foliar Damage, Ion Content, and Mortality Rate of Five Common Roadside Tree Species Treated with Soil Applications of Magnesium Chloride

Sensitivity to magnesium chloride (MgCl2) was assessed on five common roadside tree species by maintaining soil concentrations at 0-, 400-, 800-, or 1,600-ppm chloride via MgCl2 solution over four growing seasons. Evaluations of growth, leaf retention, foliar damage, and ion concentrations were conducted. Water potentials were measured on two species. Foliar chloride and magnesium concentrations were positively correlated with foliar damage in all species. Conifers exhibited mild damage during the first growing season but moderate to severe damage during the first winter and second growing season. The two highest MgCl2 treatments caused leaf loss, severe damage, or mortality of Douglas-fir, lodgepole, and ponderosa pines after two seasons of treatments and of limber pine after four seasons. Aspen also displayed foliar damage and crown loss but abscised damaged leaves and flushed asymptomatic leaves throughout the growing seasons. The highest treatment caused mortality of aspen in 4 years. Approximately 13,000–17,000-ppm foliar chloride was associated with severe damage in conifers but ranged from 13,000- to 33,000-ppm in fully necrotic leaves. Aspen foliage contained the highest concentrations of chloride (24,000–36,000-ppm), and limber pine leaves had the lowest (<14,200-ppm). Although MgCl2 caused reductions in leaf water potential, aspen and ponderosa pine did not appear to be under substantial moisture stress and continued to take up ions. Mortality of common roadside tree species in 2 to 4 years can occur due to high MgCl2 soil concentrations, and transportation officials should consider these implications in their management plans.