Soil inorganic nitrogen pulses and leaf nitrogen resorption in two Pinus hartwegii Lindl. forests

Introduction: Nutrient movement in high mountain forests generates information on their functioning and response to climate change effects. Nitrogen dynamics in these ecosystems has been poorly studied. Objective: To quantify N reservoirs in forest litter, topsoil (0-10 cm) and needle litterfall, and to measure temporal concentrations of nitrate and ammonium in topsoil and N resorption (ReabsN) in the Jocotilán (JO) and Tláloc (TL) mountains of central Mexico. Materials and methods. A total of 108 (JO) and 128 (TL) soil and needle litterfall samples were collected for one year. N and ReabsN reservoirs were compared between mountains using the Wilcoxon test (P < 0.05). Temporal trends of soil moisture, N and ReabsN forms were analyzed with linear mixed models, setting time and mountain as fixed factors. Results and discussion. Gravimetric moisture, total N, and nitrate and ammonium concentrations were not different between mountains. Total inorganic N (ammonium + nitrate) in JO was higher than in TL (46 vs. 41 mg∙kg-1). N in needle litterfall and soil were higher in JO, but ReabsN in TL was higher (60 vs. 55 %). Soil moisture, ammonium and ReabsN had a seasonal pattern of cubic trend (P < 0.05), denoting N pulses. Conclusions. Forests showed differences in N dynamics in needle litterfall, resorption and soil inorganic forms of N, indicating that it is possible to differentiate their functioning according to this nutrient.