Soil Microorganisms Increase Mobility of Iron to Rice (Oryza sativa L.) Plants

Understanding the mechanisms involved in iron toxicity tolerance of rice would help develop technologies to close yield gaps. A study was conducted aiming to understand the role of rhizosphere microorganisms in tolerance of iron toxicity in rice plants. Three varieties with different iron toxicity tolerance capacities were selected [BW 267-3 (tolerant), BW 363 (moderately tolerant) and BW 272-6b (susceptible)]. A pot experiment was conducted in a three factor factorial design including soil treatment with microorganisms (presence and absence), three iron levels in growth medium (2, 75 and 300 mg/L) and three rice varieties as grouping factors. At 42 days after germination dry matter yield and total Fe, K and P in shoots were determined. Rhizosphere oxidizing potential of each variety was determined by visualizing oxidizing power of rice roots embedded in a semisolid agar medium containing iron sulfide. Results indicated that presence of soil microorganisms significantly (p<0.05) reduced dry matter yield but increased Fe uptake of all three varieties. However, in presence of microorganisms, Fe uptake remained more consistent irrespective of the Fe concentration in growth medium. Root oxidizing power had a positive relationship with iron toxicity tolerance. The highest oxidizing potential was observed in BW 267-3. Plant-microbial interactions on growth and uptake of Fe, K and P were more prominent in BW 363 and BW 272-6b compared to BW 267-3. We conclude that microorganisms mobilize Fe to rice plants. Further, remarkable differences exist between rice varieties in root oxidizing power and plant-microbial interactions depending on their iron toxicity tolerance.