Shoot and Root Responses of Mung Beans (Vigna radiata L.) to Changing Solution Phosphorus Conditions

Context: Previous research using soil has shown that mung bean (Vigna radiata L.) exhibits minimal root length response to elevated soil solution P concentrations, so does P uptake rate compensate? Aim: We hypothesized that when a mung bean plant growing in a nutrient solution low in P accesses a short-term adequate P supply it would increase P uptake through root plasticity. Methods: Mung bean seedlings were grown for 33 d in nutrient solutions with P concentrations of ranging from 1.6 to 6.6 mg L-1 and then transferred to an 8.2 mg L-1 P, P-32 labeled solution and plants harvested 4 and 9 d after transfer. Key results: Plant growth and P uptake were increased by increasing short-term P supply. P uptake from the transfer solution doubled in the low P plants between 4 and 9 d, while in the high P plants there was a 2.5-fold increase. After 9 d in the transfer solution, 26.0% of the P in the low P plants was derived from the transfer solution compared to 18.3% in the high P plants. Between 4 and 9 d, total root length doubled in the low P plants and there was no significant increase in the high P plants. Conclusion: The results indicated that an increase in fine root length was the primary mechanism responsible for the increased P uptake upon transfer to a high P solution. Implications: In low P soils banding of P will result in increased root and shoot growth in mung beans.