Fig. 1

Effect of humic acid (HA) on maize seedlings biomass accumulation for root (a mg per seedling) and shoot (b mg per seedling and exudation yield per maize seedling (c mg/g dry root/min). Data represent normalized means from four seedlings per treatment in each case. The means were tested against control and were labeled with * and ** when assessed as significant (F test, p < 0.05 and p < 0.01, respectively). Bars represent a standard deviation. Measurements of ¹⁴C activity in aliquots of root exudate trap solution after a 30-min pulse feed to chamber atmosphere (d). In all cases, the treatments (control and humic acids at 3.5 mM) were applied during 7 days and the plants were washed and transferred to ultrapure water immediately before ¹⁴C pulse