Increased soil nitrate losses under mature sugar maple trees affected by experimentally induced deep frost

This work reports and discusses data gathered during soil solution monitoring that was part of an experiment conducted in the Duchesnay Experimental Forest (Quebec, Canada) to study the effects of induced deep frost, superficial frost, and superficial frost plus drought on mature sugar maple trees (Acer saccharum Marsh.). Frost treatment was applied by preventing snow from accumulating under the canopy. Soil solution chemistry was modified when mature sugar maple trees declined after exposure to a severe deep frost. The first vegetation period after treatment showed that losses of NO3- below the rooting zone were greatly increased under affected trees. The leaching rate of NO3- and basic cations was directly related to the level of change in canopy dieback and transparency. A mean NO3- concentration of 630 micromoles(c).L-1 (53 times the controls max. 4500 micromoles(c).L-1) was measured in soil solution under the deep frost treated trees. The leaching rate of K+ (18x, relative to the control) and Mn2+ (11x) was higher than that of Mg2+ (5x) and Ca2+ (2.6x). Acidification of the soil solution (50% more H+) as a result of intense nitrification caused an increase in aluminum concentration (5x) and a decrease in SO4(2-). The acidification during the year after treatment was equivalent to decades of atmospheric acid deposition. The seasonal mean of SO4(2-) did not differ between treatments, but there was evidence of a significant correlation between pH and SO4(2-) in soil solution. Concentration of NH4+ was also enhanced but to a lesser degree (10x) than that of NO3-. Specific conductivity was a good predictor of NO3-, Ca2+, Mg2+, and total Al in soil solution. The ion balance shifted from an anion deficit to a strong cation deficit when NO3- concentrations were high. Superficial frost with or without induced summer drought did not cause any significant change in soil solution chemistry compared with the controls