Mineralization of nitrogen compounds in the soil under the bilberry-sphagnum birch forest (Yaroslavl Oblast)

Net mineralization of nitrogen was measured in the horizons of peaty podzolic gley soil (At1, 0–6 cm, At2, 6–10 cm, and A2, 10–20 cm) of the bilberry-sphagnum birch forest from May to the beginning of November in 2011 and 2012; it comprised 2.1 ± 0.4, 2.7 ± 0.4, 1.2 ± 0.4, and 1.9 ± 0.2, 1.9 ± 0.2, 0.8 ± 0.15 g N/m2, respectively. The total of 6 ± 0.7 and 4.6 ± 0.3 g N/m2 were mineralized in the soil profile in the years 2011 and 2012, respectively, with the contribution of ammonification being more than 99%. The seasonal variations in nitrogen mineralization correlated with the temperature and soil moisture content in At1 and At2 horizons. The efficiency of nitrogen mineralization in soil horizons under the birch forest was expressed by similar values, namely, 0.005 ± 0.0008, 0.0064 ± 0.0008, and 0.003 ± 0.001 mg N/g C per day, and this suggests a high efficiency of substrate utilization in the eluvial part of the soil profile. The seasonal variation of carbon dioxide production correlated with the ammonification in the At1 horizon with r = 0.85 and p = 0.03 in 2011 and 2012, and in the At2 horizon with r = 0.65 and p = 0.16 in 2012. Over the studied period, production of ammonia depended on soil moistening in the dry year of 2011 (r = 0.91; p = 0.01) and soil temperature in the wet year of 2012 (r = 0.78; p = 0.06). The productivity of the process equaled 3 ± 0.9 mg N/m2, or 30 g N/ha in both years of observation.