Agroforestry (AF) has the potential to restore degraded lands, provide a broader range of ecosystem goods and services such as carbon (C) sequestration and high biodiversity, and increase soil fertility and ecosystem stability through additional C input from trees, erosion prevention, and microclimate improvement. Advantages and processes for global C sequestration in AF are unknown. We used a meta-analysis of 427 soil C stock data pairs grouped into four main AF systems-alley cropping, windbreaks, silvopastures, and homegardens-and evaluated changes in AF and adjacent control cropland or pasture. Mean soil C stocks in AF (1-m depth) were 126 Mg C center dot ha(-1), which is 19% more than that in cropland or pasture. The highest C stocks in soil were in subtropical homegardens, AF with younger trees, and topsoil (0-20 cm). Increased soil C stocks in AF were lower than aboveground C stocks in most AF systems, except alley cropping. Homegardens stored the highest C in both aboveground and belowground, especially in the subsoil (20-100 cm). Advantages of AF ecosystem services focusing on mechanisms of belowground C sequestration were analyzed. AF could store 5.3 x 10(9) Mg additional C in soil on 944 Mha globally, with most in the tropics and subtropics. AF systems could greatly contribute to global soil C sequestration if used in larger areas. Future investigations of AF should include (a) mechanistic- and process-based studies (instead of common monitoring and inventories), (b) models linking forest and crop growth with soil water and C and nutrient cycling, and (c) accurate assessments of the AF area worldwide based on the remote sensing approaches.

中文翻译：

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农林业系统：土壤碳储量、固存过程和未来潜力的元分析

农林业 (AF) 具有恢复退化土地的潜力，提供更广泛的生态系统产品和服务，例如碳 (C) 固存和高生物多样性，并通过来自树木的额外碳输入、侵蚀预防和小气候改善。AF 中全球 C 封存的优势和过程尚不清楚。我们对 427 个土壤碳库数据对进行了荟萃分析，这些数据对分为四个主要的 AF 系统——小巷种植、防风林、林场和家庭花园——并评估了 AF 和相邻对照农田或牧场的变化。AF（1 米深度）的平均土壤碳库为 126 Mg C 中心点 ha(-1)，比农田或牧场高 19%。土壤中碳储量最高的是亚热带家庭花园、有幼树的 AF 和表土（0-20 厘米）。在大多数 AF 系统中，AF 中增加的土壤碳储量低于地上碳储量，除了胡同种植。家庭花园在地上和地下都储存了最高的 C，尤其是在底土（20-100 厘米）中。AF 生态系统服务的优势重点分析了地下固碳机制。AF 可以在全球 944 Mha 的土壤中储存 5.3 x 10(9) Mg 额外的 C，其中大部分在热带和亚热带。如果在更大的地区使用 AF 系统，它可以极大地促进全球土壤碳封存。AF 的未来调查应包括 (a) 基于机制和过程的研究（而不是常见的监测和清单），(b) 将森林和作物生长与土壤水和碳以及养分循环联系起来的模型，以及 (c) 准确评估基于遥感方法的全球 AF 区域。