Root-soil physical and biotic interactions with a focus on tree root systems: A review

Our perception of plants is determined by their visible organs: stem, branches and leaves. The underground parts of a plant are rarely seen; indeed the root system is usually hidden from sight. This is also reflected in science where the interaction between leaves and the atmosphere is much more studied than interactions between roots and soil. One reason for such an imbalance involves the difficulties in studying roots in their heterogeneous and opaque environment. Consequently, relatively little is known about the importance of roots in the soil and how soil physico-chemical properties and soil organisms are influenced by the presence of roots and vice versa. Roots are not merely a passive agent that grow in a challenging environment: roots are engaged in a tremendous number of interactions with soil, which change soil properties and enhance its biotic component. This paper reviews the current state of understanding on the factors involved in root-soil interactions, bearing in mind the specific aim of underlining more recent advances to identify significant gaps in this research field. We also promote a tree-oriented view of roots, describing how soil physico-chemical properties, micro- and macro-fauna, symbiosis and pathogens affect tree root growth and how roots can interact and modify these abiotic and biotic factors. We hope our review will provide an impetus for more studies on the intricate soil-root interactions to enhance the importance of this vast, and somewhat hidden topic.