EFFECTS OF COMPETITION ON SPATIAL-DISTRIBUTION OF ROOTS OF BLUE GRAMA

The spatial distribution of roots of the perennial grass blue grama [Bouteloua gracilis (H.B.K.) Lag. ex Griffiths] was evaulated under 2 competitive conditions. The radioistope C-14 was used to label roots of blue grama plants growing with and without neighboring plants of the same lifeform. The majority of labeled blue grama roots (> 75%) were found within 5 cm of the plant and within 10 cm of the soil surface. Labeled roots extended at least 30 cm from the edge of the plant and to depths of at least 90 cm. Root system morphology was insensitive to changes in competitive conditions. Based on our estimates of the depth and breadth of the root system of an average blue grama plant, roots associated with at least 4 other blue grama plants of average size and separated by average distances of 10 cm might occur within the volume of soil associated with roots of this plant. The distribution of total root biomass was not representative of the distribution of labeled roots, even when neighboring grasses were removed.