Purpose

Soil respiration and N-mineralization are key processes in C and N cycling of terrestrial ecosystems. Both processes are limited by soil temperature, moisture and nutrient content in arid and cold ecosystems, but how soil nutrient addition interacts with increased precipitation requires further investigation.

Methods

The experiment consisted of 4 treatments: a) control, b) fertilization, applying 100 kg N yr⁻¹ and 75 kg P yr⁻¹, c) irrigation, increasing the average annual rainfall by 20–25%, distributed in 6–8 irrigation events, and d) irrigation+fertilization. We measured soil respiration and N-mineralization throughout seasons.

Results

Increases in annual precipitation had no effects on long-term soil respiration in any season. However, soil nutrient enrichment increased soil respiration by 19% during the plant growing season, and also increased root density by 30–45% throughout the year. The combined N + P and water addition did not increase soil respiration more than the nutrient addition alone. N + P addition had negative impacts on N-mineralization, resulting in N-immobilization. However, soil ammonium and nitrate content increased with N + P addition all over the seasons.

Conclusion

Moderate increases in the total annual precipitation lead to no long-term response of soil processes in Patagonian steppe. However, with higher soil nutrient input, such as with anthropogenic N deposition, soil CO₂ effluxes are likely to increase, and microbial biomass could retain more nutrients in the soil. Therefore, high levels of soil N enrichment in arid ecosystems may strengthen the positive feedback between C cycle and climate change if this increment is not compensate by higher carbon capture.

中文翻译：

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巴塔哥尼亚草原的土壤呼吸和氮矿化过程对施肥的反应比对实验降水增加的反应更大

目的

土壤呼吸和氮矿化是陆地生态系统碳氮循环的关键过程。这两个过程都受到干旱和寒冷生态系统中土壤温度、水分和养分含量的限制，但土壤养分添加如何与降水增加相互作用需要进一步研究。

方法

试验包括 4 个处理：a) 对照，b) 施肥，施用 100 kg N yr ^-1和 75 kg P yr ^-1，c) 灌溉，年平均降雨量增加 20-25%，分布在 6-8灌溉事件，以及 d) 灌溉+施肥。我们测量了整个季节的土壤呼吸和氮矿化。

结果

年降水量的增加对任何季节的长期土壤呼吸都没有影响。然而，土壤养分富集在植物生长季节使土壤呼吸增加了 19%，并且全年根系密度增加了 30-45%。与单独添加养分相比，N + P 和水的组合添加不会增加土壤呼吸。N + P添加对N-矿化有负面影响，导致N-固定化。然而，土壤铵和硝酸盐含量随着整个季节的N + P添加而增加。

结论

年总降水量的适度增加导致巴塔哥尼亚草原土壤过程没有长期响应。然而，随着土壤养分输入的增加，例如人为 N 沉降，土壤 CO ₂外排量可能会增加，并且微生物生物量可以在土壤中保留更多的养分。因此，干旱生态系统中高水平的土壤氮富集可能会加强碳循环与气候变化之间的正反馈，如果这种增量没有通过更高的碳捕获来补偿。