Effects of temperature change on soil ammonification and nitrification characteristics of communities at different succession stages

Soil from different succession stages (grassland, shrub forest, Betula platyphylla forest, Picea wilsonii-Betula platyphylla forest, and Picea wilsonii forest) and an indoor constant-temperature aerobic culture method were used to clarify the response of the soil nitrogen cycle to temperature in different succession stages of terrestrial ecosystems. The characteristics of soil ammonification and nitrification under different temperatures (15, 25, and 35 ℃) were studied. The results showed the following. 1) Soil depth significantly affected the ammonification rate, cumulative ammonification, nitrification rate, and cumulative nitrification (P < 0.01). With an increase in soil depth, the ammonification rate, cumulative ammonification amount, nitrification rate, and cumulative nitrification amount of soil nitrogen in different succession stages showed a decreasing trend, among which those in the 0–20 cm soil layer was the largest. 2) Successive communities significantly affected ammonification and nitrification rates (P < 0.01). With positive succession, the ammonification rate of soil nitrogen in succession stages other than the 0–20 cm soil layer of the grassland community first decreased, then increased, and then decreased. The ammonification rate of grassland was the highest. The nitrification rate of soil nitrogen at different succession stages first increased and then decreased, and the nitrification rate of Picea wilsonii-Betula platyphylla forest was the highest. 3) Temperature significantly affected ammonification rate, cumulative ammonification amount, nitrification rate, and cumulative nitrification amount (P < 0.01). Except for the 0–20 cm soil layer of shrub forest and Picea wilsonii-Betula platyphylla forest community, the 20–40 cm soil layer of Picea wilsonii forest, Betula platyphylla forest, Picea wilsonii-Betula platyphylla forest community, and the 40–60 cm soil layer of grassland community, the soil nitrogen ammonification rate and the cumulative ammonification amount of soil nitrogen in different succession stages increased with the increase of soil temperature (15–35 ℃), and the maximum level (154.03 mg·kg⁻¹) was detected at 35 ℃. In contrast, the soil nitrogen nitrification rate and cumulative nitrification amount in different succession stages increased first and then decreased with the increase of temperature. The maximum level (529.10 mg·kg⁻¹) was detected at 25 ℃. 4) Soil physical and chemical properties (TN, field capacity, NH₄⁺-N, and soil bulk density) at different succession stages had significant effects on soil nitrogen ammonification and nitrification rates at 15 and 25 ℃ (P < 0.05). The results of this study provide a theoretical basis for dynamic changes in soil nitrogen supply capacity and ecosystem management in this region.