Effects of Timing and Duration of Waterlogging on Cd Absorption and Accumulation by Rice Under Cadmium Stress

A pot experiment was conducted using extraneous cadmium as soil Cd contaminant for exploration of effect of timing and duration of waterlogging on rice yield and Cd accumulation in rice. Results show that rice yield lowered to a varying extent in all the flooding treatments vs CK (CI), especially Treatment WI (wetting irrigation throughout the rice growing season) and Treatments T1, T2, T3 and T4 (flooding beginning at the prime tillering stage and lasting for 1, 2, 3 and 4 weeks, respectively), which was 23.7%, 16.0%, 15.5%, 20.2% and 18.6%, lower, respectively, than CK. Cd content in brown rice decreased with duration of waterlogging, and Treatment WF (flooded throughout the rice growing season) was the lowest or only 3.4% of Treatment WI in Cd content in brown rice. Under the same waterlogging conditions, Treatment T1, T2, T3 and T4 was 27.1% (P<0.05), 46.6% (P<0.05), 56.0% (P<0.05) and 35.2% lower than Treatment F1, F2, F3 and F4 (flooding beginning at the filling stage and lasting for 1, 2, 3 and 4 weeks, respectively), respectively or 41.2% lower by mean in Cd in brown rice. Cd contents in shoots and brown rice varied along basically similar trends. Cd transport efficiency of the shoots decreased with duration of waterlogging. Cd enrichment factor of shoot and brown rice differed significantly between treatments and even by 17.8 and 28.0 times between Treatments WI and Treatments WF. All the findings demonstrate that flooding could effectively inhibit uptake and accumulation of Cd in rice, and the effect is positively related to duration of and timing of flooding, and better with the beginning of flooding at the tillering stage than at the filling stage.