Invasive Root Growth into Disturbed Soil of Two Tussock Grasses that Differ in Competitive Effectiveness

The ability to rapidly invade disturbed soil unoccupied by living roots (soil gaps) was examined for two tussock grass species that differ in competitive effectiveness. When soil gaps were created by removing a neighbouring tussock, the rate of root invasion into this space was more rapid for the grass of greater competitive ability. Agropyron desertorum (Fisch. ex Link) Schult, than for Agropyron spicatum (Pursh) Scribn. and Smith. Both species invaded gaps created later in the spring more rapidly than those created soon after snow melt. Acquisition of 32phosphorus placed in a soil gap varied greatly among individual tussocks of the same species that bordered the gap, even though the shoots of the tussocks were approximately the same distance from the radioactive soil and were of similar biomass. Total 32phosphorus acquisition from the gap was similar for the two grass species when the gap was created soon after the snow melted. Radiophosphorus acquisition tended to be greater for A. desertorum when the gap was created later in the spring (P = 0.08). Rapid root growth into soil gaps can allow a plant to occupy a greater soil volume and soil microsites richer in resources. However, greater resource acquisition due to this rapid root growth may not be immediately apparent