Development and stabilisation of soil structure via interactions between organic matter, arbuscular mycorrhizal fungi and plant roots

A clearer understanding of the mechanisms that underpin the development and stabilisation of soil structure would enable a more predictable restoration of degraded soil. A hierarchical model of soil aggregation (HM) is posited that predicts soils to be self-organising systems, mediated via interactions and feedbacks between their mineral constituents, organic matter and biotic activity, which serve to create and stabilise soil structure. To determine the contribution of these latter constituents, combinations of organic matter (compost), living plant roots (three perennial species: two woody, one grass) and a community of arbuscular mycorrhizal (AM) fungi where added to a massive mine spoil in a controlled pot experiment. It was hypothesized that the absence of any of these three components would retard the development of stable soil structure, as assessed through the development of porosity, changes in bulk density, soil water retention characteristics and water-stable aggregation following a 6 month incubation period. The concentration and content of soil organic carbon (SOC), nitrogen, cation exchange capacity and pH were also determined. All three factors, organic matter, living plant roots and AM fungi were required for the development of stable soil structure, but in complex ways. Overall, the data indicate that in the presence of adequate organic matter, plant roots are key contributors to the development of soil structure which is further stabilized by AM fungi.