Changes in root topology of the tussock perennial grass Molinia caerulea were studied in a pot experiment. The target species M. caerulea was grown alone and with Holcus lanatus or Carex hartmanii as a competitor. The root topology in three different soils (sand, humus rich soil and a mixture of both) was measured. Influence of competitive pressure on root topology was determined in terms of root biomass surrounding the target root. Whereas no simple significant changes in root topology due to soil quality were observed, an increase in competition pressure caused a shift of root topology towards a more herringbone structure. This shift was greatest in nutrient poor sand and least in humus-rich soil. In addition, an influence of individual competitors on topological changes in humus-rich soil was observed after excluding the effect of total root biomass.