RELATION BETWEEN ROOT RESPIRATION AND ABSORPTION

Abstract

Using seedlings of a pure strain of corn (Funk''s hybrid No. 517, Yellow Dent) the author measured the relationship between root respiration and absorptive activity. The evolution of CO2 was measured by changes in pH of the liquid surrounding the roots (quinhydrone method). For following the respirational activity, the micro-Winkler method of measuring the dissolved O was employed either alone or with the electrometric method of CO2 estimation. There was a distinct correlation between the absorption of rain water and the evolution of CO2. The highest rates of absorption and respiration corresponded with the times of maximum illumination in the laboratory. Plants with tops enclosed in dark chambers showed a similar relation between absorption and respiration. In other plants immediately following exposure of the tops to air of low humidity absorption dropped, recovered somewhat but fell to minimal values when moist air was introduced. Values obtained from aerated distilled water were believed to represent more nearly the respiratory activity of the root system. A similar correlation between respiration and absorption was noted when the roots were exposed to Knop''s solution. The author obtained an average of 2.6 cc. of CO2 evolved per cc. of distilled water absorbed, while the corresponding value for Knop''s solution was 4.7 cc. The energy as calculated from the respiratory exchange is 93% greater in Knop''s solution with an osmotic pressure of 1.75 atm. than in water.