Altitudinal variations of the rate and temperature sensitivity of soil nitrogen mineralization on the Qinghai-Tibetan Plateau

Changes in soil nitrogen mineralization can impact nutrient availability, and further affect plant growth. It is unclear, however, how temperature elevation in alpine grassland will affect soil net N mineralization rate (N_min) across altitudes. At six altitudes (3200–4200 m with an interval of 200 m) along a slope in Lenglong mountain in the northern Qinghai-Tibetan Plateau, we performed an in situ soil incubation experiment by using the resin-core method to assess altitudinal variations of N_min. Meanwhile, we evaluated the effects of temperature elevation on N_min and its temperature sensitivity (Q₁₀) through a soil downward transplantation experiment based on three reference baseline altitudes (3800, 4000 and 4200 m). The results showed that high altitudes generally led to low values of N_min. Structural equation modeling analysis revealed that N_min along the altitude was mainly controlled by soil temperature. Increased temperature caused by the altitude transplantation significantly elevated N_min for all of the three reference altitudes. The value of Q₁₀ was 3.4 for soil samples transplanted from the reference altitude of 4200 m, which was about twice that of the lower reference altitudes of 4000 and 3800 m.