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 (Nmin) across altitudes. At six altitudes (3200 m to 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 Nmin. Meanwhile, we evaluated the effects of temperature elevation on Nmin and its temperature sensitivity (Q10) through a soil downward transplantation experiment based on three reference baseline altitudes (3800 m, 4000 m, and 4200 m). The results showed that high altitudes generally led to low values of Nmin. Structural equation modelling analysis revealed that Nmin along the altitude was mainly controlled by soil temperature. Increased temperature caused by the altitude transplantation significantly elevated Nmin 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 m and 3800 m.