Detecting Depth and Lateral Spread of Roots of Native Range Plants Using Radioactive Phosphorus

Abstract

Radioactive phosphorus (P3’) was used to measure root depth and lateral spread of four native plant species which had been subjected to heavy grazing for many years. Compared with root excavation measurements from an earlier study on the same area, rooting depths of all species tested were found to be quite similar by the two methods. Lateral spread differed substantially, however. Roots were found to have a greater lateral spread by the P3 2 estimate. The isotope method using autoradiography was found to be a sensitive method of determining depth and lateral spread of in situ plant roots in a mixed plant community. A number of investigators have used radioactive phosphorus , P:‘” , to determine plant rooting characteristics (Aebersold 1953). Mathis et al. ( 1965) evaluated growth, activity, and varietal differences in cotton, corn, peanuts and tobacco roots using a tracer technique. Root growth of sorghums was measured by McClure and Harvey (1962) by use of radioactive phosphorus. Nye and Foster (196 1 j in Ghana determined the relative uptake and use of several short-term annual and perennial plants from various root zones using labelled Pts2. Boggie et al. (1958) in Scotland use radioactive tracers to investigate plant root systems growing in peat and mineral soils. The methodology was found very useful in both soil types, and they suggested that PsZ could be used to determine maximum rooting depth of each species composing a community. They also suggested it could be adapted for determining lateral spread of root systems. Their work was based on placement of Pnz at different levels within the soil of four different grassland communities and measuring the specific activity of Psr uptake by each species. A modification of this technique was used in the present study to determine depth and lateral spread of roots of four major species in the ponderosa pine-bunchgrass type of Colorado. Results are compared with those for a root excavation technique used by Schuster (1964) from a study made on the same heavily grazed experimental sites.