In the Sub-Sahelian region (Senegal), Faidherbia albida trees have been maintained for years in agroforestry parklands for their numerous services offered to people and to crops. The aerial crop biomass and yield are notably greater under the tree crown, but most of this biomass is exported and does not contribute to soil carbon (C) inputs. Belowground litter inputs are crucial, but little is known about the root system distribution, productivity and contribution to soil C inputs. This study aims to assess the field heterogeneity of F. albida and crop root systems along the soil profile based on the distance to the tree to evaluate the root contribution to soil C stocks.

During two successive rotations of pearl millet in 2020 and groundnut in 2021, soils and roots were sampled from two locations (Under and Far from the tree), in 5 soil layers to a depth of 150 cm and with three tree replicates. The aerial biomass was also sampled. The annual relative contribution of roots to soil C stocks was estimated as the ratio between root litter-derived C inputs (considering hypothetical root turnover only for trees and the whole root biomass for crops) and soil C stocks.

We found a similar crop root biomass density Under and Far from the tree, but the higher root:shoot ratio Far from than Under the tree confirmed the beneficial effect of trees on the aerial crop biomass. Unexpectedly, the tree root biomass density was higher at + 30 m from the trunk than Under the tree in the 30–100 cm soil layer, suggesting a long-distance soil exploration by the trees. Down to 150 cm of depth, the tree root litter contribution to soil C stocks represented 6.1 % and 7.1 % of the total root litter-derived C inputs (Under and Far from the tree, respectively). In this type of Sub-Sahelian parklands with low soil C stocks, increasing the tree density or selecting deep and highly rooted crop varieties should be favoured.

在萨赫勒以南地区（塞内加尔），Faidherbia albida树多年来一直在农林复合公园中得到维护，因为它们为人类和农作物提供了众多服务。树冠下的空中作物生物量和产量明显更高，但大部分生物量用于出口，对土壤碳 (C) 输入没有贡献。地下凋落物输入至关重要，但人们对根系分布、生产力和对土壤碳输入的贡献知之甚少。本研究旨在根据与树木的距离评估F. albida和作物根系沿土壤剖面的田间异质性，以评估根系对土壤碳库的贡献。

在 2020 年珍珠粟和 2021 年花生连续两次轮作期间，从两个位置（树下和远离树）、5 个土壤层中取样，深度为 150 厘米，并重复三个树。还对空中生物量进行了采样。根对土壤碳库的年度相对贡献估计为根凋落物衍生的碳输入（仅考虑树木的假设根周转和作物的整个根生物量）与土壤碳库之间的比率。

我们发现树下和远离树的作物根系生物量密度相似，但远高于树下的根茎比证实了树木对地上作物生物量的有益影响。出乎意料的是，距离树干+ 30 m 处的树根生物量密度高于树下 30-100 cm 土层中的生物量密度，这表明树木进行了长距离土壤探索。下至 150 厘米深度，树根凋落物对土壤碳库的贡献占根凋落物衍生碳输入总量的 6.1% 和 7.1%（分别位于树下和远离树的地方）。在这类土壤碳储量低的萨赫勒以南公园，增加树木密度或选择深根和高根作物品种应该受到青睐。