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

Abstract

Tobacco plants (Nicotiana tabacum L.) were grown under PAR [photosynthetically active radiation] 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.degree. C. Plants were sampled at 2 day intervals during exponential growth. Total dry matter and N in the whole plant and dry matter in the roots increased with PAR and temperature; however, their proportionalities were not constant. The RGRR [relative growth rate of roots] and RAR NP [relative accumulation rate of N whole plants] were nearly equal to each other at each PAR and temperature and both were approximately equal to the RARSR [relative accumulation rate of soluble carbohydrates in roots]. 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 N-supplying function of roots on the concurrent transport of soluble carbohydrate from the shoot.