Interdependence of Root and Shoot Activities in Determining Nitrogen Uptake Rate of Roots

Abstract

Tobacco plants (Nicotiana tabacum L.) were grown under PAR with accumulated daily totals of 10.5, 18.0, 25.5, 33.0, and 40.5 Einsteins m-2day-1 and day/night temperatures of 26/22 and 22/18 C. Plants were sampled at 2-day intervals during exponential growth. Total dry matter and nitrogen in the whole plant and dry matter in the roots increased with PAR and temperature; however, their proportionalities were not constant. The RGRR and RARNP were nearly equal to each other at each PAR and temperature, and both were approximately equal to the RARSR. Depending on treatment conditions, soluble carbohydrates in roots remained constant during exponential growth at 5%-9%. These results support a model for dependence of the nitrogen-supplying function of roots on the concurrent transport of soluble carbohydrate from the shoot.