Leaf litter nitrogen (N) and phosphorus (P), as the final products reflecting the foliar nutrient status after resorption, strongly influence forest production and nutrient cycling. However, our nuanced understanding of their general patterns and controls is still lacking, and whether differential regulatory mechanisms exist between climatic zones remains largely incomplete, which introduces substantial uncertainty in the comprehension of net ecosystem productivity and nutrient cycling. Here, we aimed to evaluate patterns of leaf litter N and P concentrations of broad-leaved tree species, and further quantify their controls from climatic, soil physical, soil chemical, and green foliar nutrient factors across and within the tropics and extra-tropics by updating a global dataset comprising 1171 records from 159 studies. We found that tropical tree species exhibited higher leaf litter N concentrations but lower leaf litter P concentrations than extra-tropical tree species. In contrast to previous findings, the effects of climatic and edaphic variables on leaf litter N and P concentrations are more pronounced in the tropics than in the extra-tropics. Different from past bivariate analyses of climate-nutrient relationships for leaf litter, climate exerted more indirect effects on leaf litter N and P concentrations through soil texture, hydrology, nutrient availability, and green foliar nutrients. We also observed direct effects of green foliar N and P concentrations on leaf litter N and P concentrations enhanced from tropical to extra-tropical zones. Overall, this study refines our understanding of differential controls over leaf litter N and P concentrations across climatic zones and highlights the crucial yet often overlooked role of soil physical and chemical properties. These insights further underscore the urgent need to integrate multiple climatic, edaphic, and green foliar nutrient variables into geographically explicit biogeochemical models to improve our understanding of leaf litter-driven forest nutrient cycling in response to future environmental changes for different climatic zones.

中文翻译：

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热带和外热带地区阔叶树种凋落叶氮磷的模式和控制


凋落叶氮 （N） 和磷 （P） 作为反映再吸收后叶面养分状况的最终产物，对森林生产和养分循环有很大影响。然而，我们对它们的一般模式和控制仍然缺乏细致的理解，气候带之间是否存在差异调节机制在很大程度上仍不完整，这给理解生态系统净生产力和养分循环带来了很大的不确定性。在这里，我们旨在评估阔叶树种的凋落叶 N 和 P 浓度模式，并通过更新包含 159 项研究的 1171 条记录的全球数据集，进一步量化它们对热带和外热带地区和内部的气候、土壤物理、土壤化学和绿色叶面营养因子的控制。我们发现，与温带树种相比，热带树种表现出较高的凋落叶氮浓度，但较低的凋落叶 P 浓度。与以前的研究结果相反，气候和土壤变量对凋落叶 N 和 P 浓度的影响在热带地区比在热带外地区更为明显。与过去对凋落叶气候-养分关系的二元分析不同，气候通过土壤质地、水文、养分有效性和绿色叶面养分对凋落叶 N 和 P 浓度产生更间接的影响。我们还观察到绿色叶面氮和磷浓度对凋落叶氮和磷浓度的直接影响，从热带到温带地区都有所增加。总体而言，这项研究完善了我们对不同气候区凋落叶 N 和 P 浓度的差异控制的理解，并强调了土壤物理和化学特性的关键但经常被忽视的作用。 这些见解进一步强调了迫切需要将多个气候、教育和绿色叶面养分变量整合到地理上明确的生物地球化学模型中，以提高我们对落叶驱动的森林养分循环的理解，以响应不同气候区的未来环境变化。