Auxin applications affect posttransplant CO2 exchange rate and growth of bare-rooted vinca [Catharanthus roseus (L.) G. Don] seedlings

Abstract

Uprooting and transplanting seedlings can cause root damage, which may reduce water and nutrient uptake. Initiation of new roots and rapid elongation of existing roots may help minimize the negative effects of transplant shock. In this study, seedlings with four true leaves were transplanted into diatomaceous earth and the plants were transferred to a growth chamber, where they were treated with NAA (0, 0.025, 0.25, and 2.5 mg·L-1; 36 mL/plant). The effects of drenches with various amounts of 1-naphthaleneacetic acid (NAA) on the posttransplant CO2 exchange rate of vinca [Catharanthus roseus (L.) G. Don] were quantified. Whole-plant CO2 exchange rate of the plants was measured once every 20 minutes for a 28 day period. Seedlings treated with 0.025 or 0.25 mg·L-1 recovered from transplant shock more quickly than plants in the 0 and 2.5 mg·L-1 treatments. Naphthaleneacetic acid drenches containing 0.025 or 0.25 mg·L-1 increased whole-plant net photosynthesis (P(net)) from 10 days, dark respiration (R(dark)) from 12 days, and carbon use efficiency (CUE) from 11 days after transplanting until the end of the experiment. The increase in CUE seems to have been the result of the larger size of the plants in these two treatments, and thus an indirect effect of the NAA applications. These differences in CO2 metabolism among the treatments resulted in a 46% dry mass increase in the 0.025 mg·L-1 treatment compared to the control, but shoot-root ratio was not affected. The highest rate of NAA (2.5 mg·L-1) was slightly phytotoxic and reduced the growth rate of the plants.