Temperatures in Early Post‐Transplant Growth: Influence on Carbohydrate and Nitrogen Utilization and Distribution in Tobacco1

Abstract

Tobacco plants (Nicotiana tabacum L. ‘NC 2326’) were grown in the North Carolina State Univ. phytotron unit of Southeastern Plant Environment Laboratory to examine the effects of ambient temperature on relative growth rates (RGR) of whole plants, leaves, stalks, and roots and their relative accumulation rates (RAR) soluble carbohydrates and N. RAR is calculated to be analogous to RGR and is expressed in units of weight of the component accumulated per weight if its content in the plant per day. Plants were grown under a 9‐hour photoperiod with photosynthetically active radiance of 750 einsteins‐m−2sec−1 in separate controlled‐environment rooms programmed for thermoperiods (day/night temperatures) of 18/14, 22/18, 26/22, 30/26, and 34/80 C. Plants were sampled from each thermoperiod on Mondays, Wednesdays, and Fridays, for 6 weeks after tramplanting. RGR and RAR were calculated only for the period of exponential growth which occurred within the interval from 7 to 35 days after transplanting. In general, RGR of the whole plant, leaves, stalks, and roots (RGRP, RGRL, RGRS, RGRR) were unaffected by the three intermediate thermoperiods. However, RGRP and RGRL declined at both 18/14 and 34/30 C but RGRS and RGRR declined only at 34/30 C. At all thermoperiods RGRS were greater than RGRP and RGRR were less than RGRP. RAR of N for the whole plant (RARNP) were less than RGRP but were equal to RGRR. The association of RARNP and RGRR apparently is related to RAR of soluble carbohydrates in the roots (RARSR). RARSR were equal to RGRR; thus, small (5 to 7% of dry weight) but constant pools of soluble carbohydrate were maintained in roots. Conversely, RARSP were greater than RGRP which resulted in a 40% increase in soluble carbohydrates in the whole plant during the growth period. It is proposed that both absorption of NO3‐ by roots and growth of roots are concurrently and competitively influenced by rate of flow of photosynthate to the roots.