Responses of soil available nitrogen mineralization ability to temperature and organic fertilizer addition in alpine grasslands of the Qinghai–Tibet Plateau

Nitrogen mineralization in the soil of alpine grasslands on the Tibetan Plateau is a key process affecting the global carbon and nitrogen cycle, as well as the succession of grassland ecosystems. The aim of this study was to explore the effects of temperature and organic fertilizer additions on the nitrogen availability in the soil of these alpine grasslands. Through incubation experiments involving different temperatures (5, 15, and 25 ℃) and gradients of organic nitrogen addition (0, 15, 45, and 75 kg·hm⁻²), we analyzed changes in soil nitrogen mineralization rates, mineralization potential, and mineralization reaction rate. The results showed that soil nitrogen mineralization increased with rising temperature, with values significantly higher at 25 ℃ than at 15 ℃ and 5 ℃. Organic nitrogen addition (15-45 kg·hm⁻²) significantly increased the mineralization of ammoniacal nitrogen in the soil. However, further increasing the fertilization gradient to 75 kg·hm⁻² reduced the nitrogen mineralization capacity. The soil nitrogen mineralization rate exhibited a single peak trend with increasing incubation time, and the addition of organic nitrogen could increase the nitrogen mineralization rate in alpine grassland soil, reaching its maximum under N45 treatment. Temperature determined the mineralization potential of nitrogen in alpine grassland soil, but did not significantly affect the mineralization rate, k. In summary, the addition of 15-45 kg·hm⁻² of organic nitrogen and higher temperature conditions are beneficial for enhancing the mineralization capacity of rapidly available nitrogen in the soil of alpine grasslands on the Tibetan Plateau, providing a theoretical basis for grassland management and organic fertilizer application in alpine grassland regions.