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In the subsoils, roots represent a major source of organic matter. Moreover, the C inputs from rhizodeposition, root turnover (mostly perennial species) and root mortality at harvest (annual crops) have a long residence time in soil due to slow decomposition rates. However, deeper understanding of the root impact on soil C stocks and nutrient dynamics is still required, especially in deep horizons of mixed species agroecosystems. This study aims to assess the heterogeneity of the root distribution and the root traits in two main components of an alley-cropping system, i.e. the crop and the understory vegetation strip (UVS) located under the tree rows; and to relate the root variables to soil physical, chemical and microbiological properties according to the distance from the tree and to soil depth. The experimental alley-cropping site “DIAMS” (Mauguio, France) was planted in 2017 with Robinia pseudoacacia (294 trees ha-1). In May 2020, we assessed the fine root biomass density, distribution, functional traits, chemical composition and some soil physical, chemical and microbiological properties in 3 soil layers (0-20, 20-50 and 50-100cm), 3 locations (the UVS under the tree rows, the wheat (Crop- 1m) at 1 to 2m perpendicular to the tree line (under tree shade) and the crop (Crop-4m) at 3.4 to 4.5m from the tree (no tree shade)) and in 3 independent replicated plots. The crop roots at 0-20 cm of depth had a biomass reduced by 3-fold near the UVS compared to far from it. UVS and crops showed similar root traits response to depth with a decrease of specific root length and stele diameter associated with an increase of root C:P ratio. The estimated annual root C inputs represented less than 0.6% of the organic C stocks and was less important under the UVS than the crop, at depth, due to C input pathways (turnover vs. mortality, respectively). Between 0 and 50 cm of depth, the soil C stocks increased with root C stocks, whereas below 50cm the relationship was negative, suggesting that root effect on soil-C might shift in subsoil. At all depths, the root stoichiometry had a tight link with extracellular enzyme N activities. According to ecoenzymatic stoichiometry, subsoil seemed more nutrient limited. Altogether, our results suggested that increasing root biomass up to 50 cm (in our case) can foster soil C storage. In contrast, in deeper soil layers, an increase in root inputs, having high C:N ratios, could induce microbial N limitations and consequently restraint soil C storage.

本論文では，日本有数の酒米生産地である兵庫県を対象に，地質が異なる地域で栽培された酒米を比較することで，酒米と栽培土壌の化学的性質がどのように関係するか，生産地域の土壌特性が酒米の品質にどの程度影響を与えるかに関して検討を行った。土壌試料は，堆積物地帯，玄武岩地帯，蛇紋岩地帯の地域から土壌（計20地点）を採取し，土壌中の全塩基含量，無機成分含量，および可給態窒素含量と全リン含量を分析した。酒米に関しては，堆積物地帯，玄武岩地帯の玄米の試料（計16地点）を採取し，土壌試料と同じ項目を分析した。その結果，堆積物地帯の土壌と比べ，玄武岩地帯，蛇紋岩地帯の土壌はマグネシウム，マンガン，亜鉛，鉄含量が多く存在し，その影響を受け，酒米も同様の成分が高い傾向にあることが判明した。このことは，酒米栽培土壌の地質の違いが，酒米の化学的性質の違い，ひいては日本酒の地域性を生み出す重要な要因の1つであることを示唆している。

The forest–savanna transition zone, which contains nutrient-poor soils (Oxisols), is found throughout central Africa. To evaluate the effect of deforestation on soil phosphorus dynamics, which regulate the plant growth in this area, we quantified the relationship between phosphorus (P) and carbon (C) in different fractions and compared their relationship to forest and savanna (deforested vegetation) in eastern Cameroon. We analyzed the P, C, and nitrogen (N) contents of soil using the physical fractionation method (0.25–2.0 mm as macro-particulate organic matter [M-POM]; 0.053–0.25 mm as micro-POM; and −1) than that in savannas (3.4–4.0 Mg P ha−1), though soil C and N stocks were similar between the vegetation. We also observed lower soil P stock in the active fraction (M-POM) with its higher C:P and lower C:N ratio in forest surface layer (0–10 cm), indicating that forests have lower available soil P. By using the regression analysis, we found a clear relationship between P and C in the stable fraction (Clay+silt) of the upper layer (0–40 cm) for each land management, and the coefficient of the regression was clearly different between the forest and savanna. It indicates that a more chemically complex organic P form of the stable fraction exists in forest soil than in savanna soil. These results indicate that the deforestation (savannazation) affect the active and stable P dynamics and it should cause the lower soil P stock of the upper layer in savanna than in forest.