Purpose

Vast expanses of climatically sensitive ecosystems, such as tropical montane, remain unstudied in terms of factors controlling nitrogen (N) availability and in turn productivity. Temperature and elevation are two important, yet understudied, factors which decide the fate of N in montane ecosystems. Therefore, the present study aimed to quantify and understand changes in rates of N transformation processes in tropical montane soils of the Himalayas under different temperature-elevation conditions.

Materials and methods

The ¹⁵N isotope dilution technique was employed to quantify the rates of gross N transformations in soils collected at two depth intervals (0–20 cm and 20–40 cm) from five elevations (3000 m, 2500 m, 2000 m, 1500 m, and 1000 m above sea level) of the Garhwal Himalayas. The rates were measured at low (10 °C) and high temperature (23 °C) conditions to decipher the effect of temperature change on N cycling in montane soils.

Results and discussion

The results indicated a significant increase in gross N mineralization rates under the high temperature condition compared to the low. Interestingly, gross nitrification rates remained unaffected of temperature change. Increase in gross N mineralization at high temperature condition was accompanied with increased ammonium (NH₄⁺) consumption, which was largely in the form of NH₄⁺ immobilization. In general, gross N transformation rates in the top soils showed higher response to change in temperature and elevation conditions than the bottom soils.

Conclusion

Increase in rates of N mineralization and other soil N cycling processes at higher temperature suggests potential acceleration in N turnover due to warming in the Himalayan soils. Increased NH₄⁺ immobilization and poor sensitivity of nitrification to temperature are likely to increase soil N conservation at higher temperature. The inconsistent variation in N transformation rates with elevation suggested higher control of edaphic factors on soil N cycling at a particular elevation.

中文翻译：

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不同温度和海拔条件下喜马拉雅土壤中的氮转化率

目的

就控制氮（N）的利用率以及进而影响生产力的因素而言，尚未对气候敏感的生态系统（如热带山地）的广阔范围进行研究。温度和海拔是决定山地生态系统中N命运的两个重要但尚未研究的因素。因此，本研究旨在量化和了解不同温度升高条件下喜马拉雅山热带山地土壤中氮转化过程速率的变化。

材料和方法

的¹⁵是采用Ñ同位素稀释技术定量总Ñ变换土壤中在两个深度间隔收集来自五个凸起率（0-20厘米和20-40厘米）（3000米，2500米，2000米，1500米，和海拔1000 m）的Garhwal喜马拉雅山。在低温（10°C）和高温（23°C）条件下测量速率，以了解温度变化对山地土壤氮循环的影响。

结果和讨论

结果表明，与低温相比，高温条件下总氮矿化速率显着增加。有趣的是，总硝化速率不受温度变化的影响。高温条件下总氮矿化的增加伴随着铵（NH ₄ ⁺）消耗的增加，这主要以固定NH ₄ ⁺的形式出现。通常，表层土壤的总氮转化率显示出对温度和海拔条件变化的响应比底层土壤更高。

结论

较高温度下的氮矿化速率和其他土壤氮循环过程的增加表明，由于喜马拉雅土壤的变暖，氮素周转的潜在加速。NH ₄ ⁺固定化的增加和硝化对温度的敏感性差，可能会增加高温下的土壤氮素养护。随着海拔的升高，氮素转化率的变化不一致，这表明在特定海拔高度，土壤中氮素的养分因子控制较高。