Fructan production in Vernonia herbacea (Vell.) Rusby is related to adequate nitrogen supply and period of cultivation

(Fructan production in Vernonia herbacea (Vell.) Rusby is related to adequate nitrogen supply and period of cultivation). Previous studies showed that plants of Vernonia herbacea grown for one year under a limited nitrogen supply presented reduced growth and higher fructan content than plants treated with sufficient nitrogen supply. However, the total fructan production was similar in both plant groups due to the higher biomass of the underground reserve organ in nitrogensufficient (N-sufficient) plants. In the present study we aimed to evaluate if a stress growing condition under nitrogenlimited (N-limited) supply, following cultivation under N-sufficient supply would have a positive effect on fructan production. Plants cultivated during one year under N-sufficient supply (10.7 mmol L N-NO3) were separated in two groups. During the following six months, one group continued to receive the same treatment (control) while the other received an N-limited supply (1.3 mmol L N-NO3). Growth, photosynthesis and soluble carbohydrates were measured at days 0, 30, 60, 90 and 180. At day 30, plants transferred to N-limited supply showed a significant increase in growth and a decrease in fructan concentration, as a response to the stressing condition. However, in the following period growth was reduced and fructan concentration was increased, confirming the inverse relationship between nitrogen concentration and fructan content. After 180 days, although the fructan concentration in N-limited was significantly higher, with a fructan production of 6.0 g plant, the higher gain in rhizophore biomass after 18 months of cultivation in N-sufficient solution led to a fructan production of 8.3 g plant, thus surpassing the higher fructan concentration of N-limited plants.