The impacts of agroforestry on soil multi-functionality depending on practices and duration

Agroforestry systems provide a wide range of soil multiple functions (that is, soil multi-functionality) to human society, including the regulation of nutrients and water in soils and the sequestration of atmospheric carbon dioxide, whereas howthese effects varied with agroforestry practices and environmental conditions remain unclear. Here, by comparing the soil multi-functionality in agroforestry systems to forests through the field experiment and global scale metaanalysis, we tested, 1) how agroforestry affected soil multi-functionality in a single field study and at the global scale, 2) whether the effects of agroforestry on soil multi-functionality changed in different agroforestry practices, 3) whether the effects of agroforestry on soil multi-functionality varied with environmental conditions. Our study showed that most of the soil functions in agroforestry systems is higher than in forests at the global scale, but show no significant differences between agroforestry and planted forests in our field study. We also found that the effects of agroforestry on soil multi-functionality were varied with agroforestry practices, showing a greater positive in forest-herbage systems than in other practices. In addition, the positive effects of agroforestry on soil organic carbon and total phosphorus declined with the extension of experimental duration. Furthermore, our analysis found that climate conditions had a minor effect on the effects of agroforestry on soil functions. Our analysis revealing that the effects of agroforestry on soil functions depend on agroforestry practices, highlighting that the effects of agroforestry may be diminished with age, and suggesting that the evaluation of ecological impacts of agroforestry should be based on long-term experiments across multiple practices.

农林业系统（Agroforestry systems）可为人类社会提供丰富多样的土壤多功能性（soil multi-functionality）服务，涵盖土壤养分与水分调控、大气二氧化碳固存等环节，但其效应随农林业实践模式与环境条件的变化规律尚未明确。本研究通过野外实验与全球尺度荟萃分析（meta-analysis），对比农林业系统与天然林的土壤多功能性，验证了三个科学问题：1）在单站点野外研究与全球尺度下，农林业如何影响土壤多功能性；2）农林业对土壤多功能性的效应是否因不同农林业实践模式而异；3）农林业对土壤多功能性的效应是否随环境条件改变而发生变化。研究结果显示，全球尺度下农林业系统的多数土壤功能均显著高于天然林，但本项野外研究中，农林业与人工林（planted forests）之间未观测到显著差异。此外，本研究发现农林业对土壤多功能性的效应因实践模式不同而存在显著差异：林草复合系统（forest-herbage systems）的正向效应显著高于其他实践模式。进一步分析表明，农林业对土壤有机碳与总磷的正向效应随实验周期延长而逐渐减弱。此外，本研究的分析结果显示，气候条件对农林业土壤功能效应的影响相对较弱。本研究揭示，农林业对土壤功能的效应取决于其具体实践模式，同时表明其效应可能随系统存续时长增加而减弱，并提示评估农林业的生态影响需基于覆盖多种实践模式的长期野外实验。