Study On The Formation Of Iron Plaque Induced On The Rice Root Surface By Phosphorus Deficiency And The Effects On As Accumulation In Rice Seedlings

Phosphorus is a necessary macronutrient for crop growth, which is one of the mainnutrient elements that restrict high yield and high quality of the crops. It’s a fact that riceroot can form iron plaque to adapt to the flooded environment. Studying mechanism of theiron plaque formed on rice roots, holds a great importance of ecology on absorbing ofheavy metals and nutrient elemenst. Therefore, it is necessary to identify whether it is theonly characteristic of rice to form the iron plaque on the rice root surface under Pdeficiency and the position of iron plaque.Fe(II)-EDTA and Fe(III)-EDTA were used to study the effects of different forms ofiron sources on the formation of the iron oxides on roots of rice. The hydroponicexperiment was conducted to study whether the levels of the iron oxides’ formation on riceroots has a relevance to phosphorus concentration in nutrient solution. Finally, the soil withlow phosphorus and high arsenic from arsenic pollution area was collected to studydifferent phosphorus concentrations affect rice growth in arsenic pollution soil and thearsenic accumulating in the rice. The main results were as follows:(1).Iron plaque induction on root surface under the P starvation is the specific property ofrice. The iron plaque is distributed in the space of cell wall unevenly using microscope. Pstarvation for2weeks could increase root lengths of the crops. The root lengths of rice,wheat, corn and soybean under the P starvation are increased significantly by11%,11%,20%and11%compared to those of the P sufficiency, respectively (p<0.05). The ironplaque induced by P deficiency on the rice root surface enhances the sequestration of otherelements in the plaque, such as Ca, Fe, Mn, Cu and Zn, and could be a buffer or reservoirof nutrient elements into rice roots, especially for Fe. For other crops, the P starvation doesnot the significant effects on other nutrients levels in roots and shoots. The P deficiency fora short period does not influence the uptake and translocation of K, Ca, Fe，Mn, Cu and Znof wheat, corn and soybean. Iron plaque formation on the rice roots under the P deficiencyinhibits the Fe translocation from roots to shoots of rice. In addition, the P starvation doesinfluence the concentrations of other nutrients in roots and shoots of rice.(2). When rice seedlings grew in nutrient solution with Fe（II）-EDTA and Fe（III）-EDTA under P or P0treatment for one week, it was found that iron plaque was indued only on therice roots with supply of Fe（II）-EDTA under P0treatment.(3). Phosphorus deficiency results that the concentration of the iron oxides of the rice rootsurface is gradually going down with the increasing of the phosphorus concentration.Under the phosphorus deficiency condition, the Iron oxides on rice roots were more thanthat under normal phosphorus supply condition. The critical phosphorus concentration ofIron plaque on rice roots is0.05mM. The quantity of the Iron plaque on the surface of riceroots is significantly negative correlation with phosphorus concentration in nutrientsolution (r=0.900, P<0.05).(4). Under natural arsenic pollution soil, the rice couldnot grow without phosphorus. Theplant height had no change during the experimental period and the plant is withered andyellow, and nearlyto death. After the phosphate fertilizer provided, the plant height issignificantly improved. And with the increasing of the phosphorus concentration, the plantheight is continuously increased. Therefore, the phosphorus concentration of soil is one ofthe significant factors, which influences arsenic’s fuction on the the biologicaleffectiveness. With the increasing of phosphorus concentration of the soil, there is asignificant rise of arsenic concentrtiont in soil solution, which means that the increasing ofphosphorus concentration of the soil enhanced arsenic released from soil particles.Moreover, there is definitely significant correlation between arsenic concentrations in therice roots and the phosphorus concentrations in soil solution. That indicated that higherphosphorus concentration in soil solution significantly improved the arsenic accumulationin the rice roots, and restrained the arsenictransferring from the roots to the shoots.Therefore, phosphate fertilizer can be used in some heavy arsenic polluted areas to increasethe yield of rice and reduce arsenic contamination to plants.