Distribution of photo-assimilated ¹⁴carbon in the root system of a shortgrass priarie

Abstract

Shortgrass prairie plots (0· 5 m²) dominated by Bouteloua gracilis were labelled by liberating 14CO₂ from a Na₂ ¹⁴CO₃ solution inside polyethylene tents on 26 May, 12 July, and 13 September 1972. Three days after labelling, roots were sampled to a depth of 60 cm in 5-cm segments. Functional and non-functional roots were separated through autoradiography. Functional roots were combusted in a micro-bomb, and the CO₂ released was absorbed in alkali. An aliquot of this solution was radio-assayed in a liquid scintillation counter in order to assess the specific activity of roots of different depths at different times in the growing season. About 62% of the roots receive the label, and there is an indication that with the advance of the growing season there is increasingly more storage of assimilates in the roots of upper depths. The roots of deeper layers are mostly replenished during the early part of the growing season.