Aggregation of a Silty Clay Loam Soil by Mycorrhizal Onion Roots

Abstract

AbstractOnion plants (Allium cepa L.) inoculated in the root zone with a vesicular‐arbuscular mycorrhizal (VAM) fungus, or left uninoculated, were grown in potted soil for 230 d to determine the influence of the VAM fungus (Glomus macrocarpum Tul. and Tul.) on soil structure. The silty clay loam soil was maintained at a moisture content between 25 and 30%. Paired inoculated (+M) and uninoculated (−M) plants were harvested (20 pairs over 150 d) beginning 80 d after planting. Relationships between plant, fungal, and soil parameters and changes with time were evaluated by regression analysis. Root colonization by the VAM fungus in +M plants ranged from 49% to 60% over the sampling period, while no mycorrhizae were detected in the ‐M plants. Total dry mass of VAM plants was five to six times that of the non‐VAM plants. Soil from the +M treatment was significantly better aggregated, more porous, and had greater water permeability than ‐M soil. Root dry mass and VAM hyphal density in the +M soil were both significantly correlated with the relative abundance of water‐stable soil macroaggregates. Correlation of root mass with aggregate abundance was stronger, however, suggesting that soil changes were mainly mediated by direct root effects of a host plant whose growth was stimulated dramatically by its VAM fungal endophyte.