Root and shoot development in ornamental shrubs: The influence of compacted soil and altered root geometry

Abstract

Root systems are expected to ‘perform’ in a variety of difficult and stressful urban soil environments. Experiments were conducted to simulate compacted soil conditions and altered rhizosphere geometry to determine how these factors affect root development and subsequent plant quality. Comparisons were made across three common landscape shrubs; Philadelphus cv. Aureus, Philadelphus cv. Belle Etoile and Euonymus cv. Silver Queen. A factorial experiment investigated three levels of compaction (control, medium and high compaction) across three soil types (organic, clay and sand). High compaction was detrimental to root extension in clay and organic soils, but had no effect in sand. Reductions in shoot extension corresponded to restricted root development. In a second experiment artificially altering the geometry of the rhizosphere was implemented by growing plants in 1/ tall, narrow columns, 2/ shallow trays or 3/ conventional pots. Despite plants being grown in identical volumes of media and provided with similar irrigation regimes, total root weight and root branching was reduced in the narrow columns, with again a corresponding reduction in top growth. The results have implications for how plants respond to stresses related to compacted soils and unusual soil profiles. The data confirm previous studies in that there are significant negative factors encountered with typical urban soils, but under certain scenarios there may also be some beneficial effects with respect to plant morphology. These will be discussed