Peat particle size effects on spatial root distribution, and changes on hydraulic and aeration properties

During ornamental plant growth, the spatial heterogeneity of root distribution in containers raises the question of air and water availability within growing media, and of their evolution during plant growth. The aim of the present study was to characterise the evolution of peat hydraulic properties in different parts of containers during root growth. A 4-month long experiment was carried out in a greenhouse in 1 L-containers at constant water regime (−1 kPa water potential). We studied Rosa “Knock Out”® growth in two different particle-size sphagnum peats, a fine one (0–10 mm) and a coarse one (20–40 mm). Every month, aerial biomass and root biomass were quantified. Root distribution was studied relative to the depth and the proximity of the container border. Water retention, hydraulic conductivity and relative gas diffusivity of the growing media were measured. The study showed that root growth increased water retention. The higher root density at the bottom of the container highlighted a potential risk of anoxia, particularly in fine peat. In coarser peat, whose porosity is more important, both hydraulic conductivity and relative gas diffusivity were improved during root growth.

► Rose root growth increased water retention capacity and improved pore effectiveness.
► Spatial root distribution strongly affected the physical properties of peat.
► Peat particle size affected air-filled porosity and unsaturated hydraulic conductivity.
► Very low rates of relative gas diffusivity were found at the base of the container.