Research On Rice Cadmium Uptake Control By Combined Regulation Of Root Zone And Leaf Blade

Heavy metal pollution in farmland was one of the major environmental problems in China, and the problem of cadmium pollution in paddy fields in southern China was particularly prominent. This reach took rice Teyou 524 as material and chose typical cadmium contaminated soil as experimental soil. By using the way of pot experiment, it researched the level of these factors, like regulation of different root zone, which included the different water management(W1: conventional water management, namely drying fields for one week in the late tillering stage and in the late maturing stage, and in other, flooding the field; W2: flooding the fields through the whole growth period), applying calcium, magnesium and phosphate fertilizer in different soil(P1: 1g·kg-1; P2: 2 g·kg-1), and leaf spraying treatments(LS: 2.0 mmol·L-1Na2SiO3, LX: 25 μmol·L-1Na2SeO3, LSX: 1.0 mmol·L-1Na2SiO3+12.5 μmol·L-1 Na2SeO3). Then it studied the effects of different combinations of these factors on cadmium uptake in rice, the changes of physiological indexes of leaves at tillering stage and the changes of pH, Eh and available cadmium content in soil. It also explored and analyzed the efficiency model and related mechanism of cadmium uptake in rice and the field experiment is also conducted in field. The main conclusions were as follows:(1)There was no significant effect on the yield of rice for root zone treatments, leaf spraying treatments and the combined treatments. However, flooding treatment could inhibit the effective tiller of rice, and the inhibitory effect is more obvious in acidic soils than in alkaline soils. Flooding treatment can improve the quality of straw. And compared with the control, the mass of straw on average in acid soil increased 36.1g, an increase of 39.9%, and the mass increase 56.2g in alkaline soil, an increase of 63.9%. The field verification showed that water was one of the important factors that affect the yield of rice. Compared with W1, the different combinations of W2 treatment made the yield of rice drop 8.7%-11.8%, an average of 10.4%. Under the same water management, the root zone management, leaf spraying treatments and combined treatments had no significant effect on the yield of rice.(2) Root zone regulation significantly reduced the available content of cadmium in soil. The comparisons of available cadmium content in soil with combined treatment were the decline of 30.8-42.5% in acid soil and the decline of 22.7%-34.3% in alkaline soil. The order of soil solution pH with different root zone treatments was as follows: W1<W2<W1P1<W2P1<W1P2<W2P2. On the contrary the order of Eh was W2P2< W1P2< W2P1< W1P1< W2 < W1. Soil solution pH was negatively correlated with the redox potential of the soil. The correlation coefficient of acid soil was-0.92, and the alkaline soil was-0.80. And soil pH was significantly negatively correlated with available cadmium content in soil, the correlation coefficient of acid soil was-0.85, and the alkaline soil was-0.68. Field test result was: the combination of root zone and leaf management can significantly reduce the content of available cadmium in soil, which was decreased by 27.9%-37.7%.(3) Combined treatment of root zone and leaf spraying significantly reduced cadmium content in rice, but the interaction between the three parts was not significant. In acid soil, the Cd content in roots, stem, leaves and grains respectively decreased 21.64%-28.94%, 30.57%-45.42%, 38.9%-55.2% and 60.42%-75.73%. And in alkaline soil, they respectively decreased 18.3%-21.24%, 26.37%-24.01%, 32.94%-44.55% and 46.32%-60.90%. Field test result was that the combined treatment of root zone and leaf spraying significantly reduced cadmium content in different parts of plant, and the drop in roots, stems and grains respectively was 29.3%-38.3%, 46.1%-63.8% and 64.8%-79.5%. The result of field experiment was consistent with the results of pot experiment. Combined treatment of root zone and leaf spraying significantly reduced the content of cadmium in rice. Among them, combined treatments of W2P2 LS, W2P2 LX and W2P2 LSX were the most effective— Rice cadmium content reached the standard(0.2 mg·kg-1), which could achieve the production safety of rice in the field of cadmium pollution.(4)Combined treatment of root zone and leaf spraying significantly reduced the transport coefficients of cadmium in different parts of plant, cadmium transportation from stem to leaf(SL) was easier than that of leaf to grain(LS) and root to stem(RS), which was RS<LS<SL. In acid soil, the drop of RS, SL and LS respectively was 10.6%-22.5%, 22.1%-31.1% and 26.1%-36.7%. While in alkaline soil, the drop respectively was 10.6%-16.5%, 8.9%-16.0% and19.9%-30.4%. Field test result was that combined treatment of root zone and leaf spraying significantly reduced the transport coefficient of rice in different parts of plant, RS and SS fall 23.8%-34.6% and 31.9%-42.6% respectively.(5) The combined regulation of root zone and leaf spraying could not only increase the chlorophyll content of rice seedlings to a certain extent, an average increase of 15.7%- 22.9%, but also increase the activity of antioxidant enzymes and relieve the peroxidation of the plasma membrane. Among them, SOD activity was the highest, an average increase of 36.2%-51.8%; POD activity followed by an average increase of 29.4%-36.1%; CAT activity was the third, the average increase of 24.6%-31.8%. Then, APX activity increased by an average of 12.5%-19.9%, However, the content of MDA decreased by an average of 19.2%-34.4%.