In terrestrial ecosystems, phosphorus (P) is the limiting nutrient of primary production. The soil organic horizon is a vital source of bioavailable P in subalpine coniferous forests. However, the response of organic horizon P to temperature increase in subalpine coniferous forests is not well characterized. By studying different decomposed degree of organic horizon across an altitudinal gradient, we aimed to simulate responses of the organic horizon P conversion to MAT increase in subalpine ecosystems. In this study, relative enrichment and relative depletion of P fractions were defined as the conversions between different P fractions. We initially observed only unidirectional conversion from labile inorganic P (LIP) to highly resistant organic P (HOP) at a mean annual temperature (MAT) of 1 °C. However, with increasing MAT, there was a relative depletion of moderately resistant inorganic P (MIP) (MAT = 2.4 °C), followed by a successive depletion of moderately resistant organic P (MOP) (MAT = 4.1 °C). Concurrently, we observed relative enrichment of labile organic P (LOP) (MAT = 2.4 °C). Combined with indoor incubation experiments, we further found that the concentration of available P peaked (81.79 mg kg) at the initial stage of MIP relative depletion (MAT = 2.4 °C), while the net P mineralization rate (2.19 mg kg d) reached a maximum following the initial relative depletion of MOP (MAT = 4.1 °C). Under elevated temperature, the pH of the organic horizon plays a crucial role in determining P fractions variation. These findings suggest that temperature increase can exacerbate the conversion of P fractions and the release of bioavailable P from organic horizon by successively triggering the relative depletion of MIP, the relative enrichment of LOP and relative depletion of MOP at specific MAT thresholds, which has important implications for the enhancement of primary production and carbon sequestration in subtropical coniferous forests under future climate warming.

中文翻译：

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温度升高加剧有机层中P组分的转化

在陆地生态系统中，磷（P）是初级生产的限制性养分。土壤有机层是亚高山针叶林生物有效磷的重要来源。然而，亚高山针叶林有机层 P 对温度升高的响应尚未得到很好的表征。通过研究不同海拔梯度上有机层的不同分解程度，我们的目的是模拟亚高山生态系统中有机层P转换对MAT增加的响应。在本研究中，P组分的相对富集和相对消耗被定义为不同P组分之间的转换。我们最初观察到在年平均温度 (MAT) 为 1 °C 时，仅观察到从不稳定无机磷 (LIP) 到高抗性有机磷 (HOP) 的单向转化。然而，随着 MAT 的增加，中度抗性无机磷 (MIP) (MAT = 2.4 °C) 相对消耗，随后中度抗性有机磷 (MOP) (MAT = 4.1 °C) 连续消耗。同时，我们观察到不稳定有机磷（LOP）的相对富集（MAT = 2.4 °C）。结合室内孵化实验，我们进一步发现，有效磷浓度在MIP相对损耗初期（MAT=2.4℃）达到峰值（81.79 mg kg），而净磷矿化率（2.19 mg kg·d）达到峰值。 MOP 初始相对消耗后的最大值 (MAT = 4.1 °C)。在高温下，有机层的 pH 值在决定 P 分数变化方面起着至关重要的作用。这些发现表明，温度升高可以通过在特定的MAT阈值下相继触发MIP的相对消耗、LOP的相对富集和MOP的相对消耗，加剧P组分的转化和生物可利用的P从有机层的释放，这具有重要意义。在未来气候变暖的情况下提高亚热带针叶林的初级生产和碳固存。