The Effect of Ascorbic Acid, when Applied to the Rooting Medium, on Nodulation and Nitrogen Fixation in Gram (Cicer arietinum)

Plants of a pure line variety, G 24, of Cicer arietinum L. were grown in sand culture. After an initial dose of a complete nutrient solution, a nitrogen free nutrient solution was supplied to the sand at intervals and a standard rhizobial culture was added twice. The plants were treated with two concentrations of ascorbic acid (20 mg/l and 100 mg/l) through the rooting medium. At suitable intervals two pots from each treatment were sampled. Observations were made regarding the earliest initiation of nodulation, the number, weight and colour of nodules and the nitrogen content of different plant organs under various treatments. Ascorbic acid (AA) treatments considerably enhanced nodule initiation. AA was found to increase the number and the fresh and dry weights of nodules tremendously and maximally under both concentrations used. The nodules were, on the whole, more pink under AA treatments and their greening was considerably delayed thus increasing their functional span. The nitrogen content of AA-treated plants was over 2.5 times that in the control. This increase in nitrogen content fully reflected itself in growth by an increase in the weight of all plant organs. Treatment with 20 mg/l AA stands out prominently above all others in this respect. Pod formation started earlier and the pod and seed weights were also much higher in the AA treatments than in the control. Treatment with 20 mg/l AA was on the whole more promotive than that with 100 mg/l. The enhancement in the nodulation and the functional efficiency of nodules by AA treatments has been attributed to the capacity of AA to increase the loci and rates of cell division by promoting nucleic acid and protein synthesis and its action as a powerful electron donor. The results show that nodulation is yet another phenomenon wherein AA plays the role of an important hormone.