INFLUENCES OF SEASONAL TEMPERATURE ON NITROGEN AND SULFUR MINERALIZATION/IMMOBILIZATION IN A MAPLE-BIRCH FOREST FLOOR IN CENTRAL ONTARIO

Abstract

Net mineralization of sulfur (S) and nitrogen (N) and nitrification in an F(Oe) horizon were examined over a 16-wk period (May to September) with (a) buried bags, (b) lysimeters and (c) closed flasks at 10, 20 or 30 °C. The amount of [Formula: see text] plus [Formula: see text] extracted from soil held at 33 kPa tension over 16 wk, when extrapolated to the mass of soil in the field, was 30 kg ha−1 N and 9 kg ha−1[Formula: see text] at constant 20 °C in the flasks, and 33 kg ha−1 N and 4 kg ha−1[Formula: see text] in buried bags (mean daily temperature 15.2 °C). On the basis of lysimeter data there was a net release of only 8 kg ha−1 N and a net retention of 3 kg ha−1[Formula: see text] under field conditions, with fluctuating temperature and moisture and actively absorbing roots. Nitrate recovered from the three types of experiment was equivalent to 18, 36, and 4 kg ha−1 N, respectively. Mineralization appeared to be particularly sensitive to temporal changes in average daily temperatures in the field. The late-summer peak in mean daily forest-floor temperature triggered a shift from net mineralization to net immobilization of N. Key words: Soil temperature, forest floor, sulfate, ammonium, nitrate