Abstract: Solution culture is conducted to investigate the effect of root iron plaque on zinc uptake by rice plant. The results show that under anaerobic condition,oxygen release from root to rhizosphere causes the formation of precipitated iron oxides or hydroxides plaque on root surface,which influences the zinc uptake by plant.If less iron plaque is existed the zinc uptake can be enhanced. When the amount of iron plaque were 12100 mg·kg^-1 root DW,the zinc uptake by rice reaches to maximum.However,with increasing amount of iron plaque(more than 12100 mg· kg^-1 root DW),the zinc is inhibited, and the plaque becomes a barrier for zinc uptake. Under Fe deficiency,the exudates of rice root,especially phytosiderophore,play an important role in zinc uptake by rice root with plaque,and the significance of phytosiderophore in zinc uptake is correlated with the amount of iron plaque.If the plaque is less,phytosiderophore appeares to enhance the zinc uptake. With increasing amount of iron plaque, the role of phytosiderophore in mobilizing zinc absorped on plaque becomes less important.Therefore, iron plaque on rice root could be either a beneficial reservoir or a barrier for zinc uptake by rice plant, which depends on the amount of iron plaque.

Key words: Iron plaque, Rice, Zinc uptake, Phytosiderophore, the middle reaches of Heihe River, land use transition, ecological quality, ecological grade