磷肥调控水稻摄取积累Cd的根际过程与机制

How to control the transformation of cadmium from soil to plant is an urgent issue worldwide. The chemical behavior of cadmium in the rhizosphere is the critical process for the regulation of its transfer in the soil-plant systems. Nowadays, phosphate application is considered as a win-win agronomic repair measure due to its nutrient supply and heavy metal control. However, the literatures reported about the effect of different phosphate fertilizer and its application rate on cadmium phytoavailability showed significantly different, and the impacts of phosphate on cadmium behavior in rhizosphere are still poorly known. In this study, the effects of different phosphate source and its application rate on cadmium uptake by rice were investigated under field and pot conditions.And the rhizosphere ecological effects induced by phosphate and its influence on cadmium form and transformation would be further studied by determining the rhizosphere and non-rhizosphere soil physical and chemical properties, cadmium form and adsorption -desorption behaviors based on a multilayer rhizospere box test. Moreover,the effects of root surface iron plaque and exudates induced by phosphate on cadmium behavior would also be explored by determining soil cadmium adsorption, complexation and dissolution. Scanning electron microsope images of rhizosphere soil and rice root would be analyzed to understand whether cadmium phytoavailability is impacted by formating phosphorus cadmium sedimentation. The expected research results would provide a scientific basis for using phospherous fertilizer to repare cadmium polluted paddy soil in future.

控制土壤镉对植物的污染是当前迫切需要解决的问题，镉在土壤根际中的化学行为是调控其在土壤-植物系统迁移的关键。施用磷肥被认为是兼顾营养与重金属治理的双赢农艺修复措施。然而，不同磷肥及施磷量对土壤镉的植物有效性影响不一致，其调控镉根际摄取过程及机制缺乏足够的认识。本研究拟通过比较大田、盆栽条件下不同磷肥及施磷量下水稻对镉的吸收、累积变化，筛选出对稻田镉植物有效性差异大的磷肥和施磷量。在此基础上，采用多隔层根际箱培养试验，通过分析非根际、不同根际微域土壤的理化性质、镉形态及镉吸附-解吸变化，阐明磷肥诱导的根际生态效应及其对镉的赋存形态、转化影响；研究水稻根系铁膜、分泌物对土壤镉的吸附、络合和溶解作用，探讨磷肥诱导的水稻根系铁膜及分泌物变化对土壤镉化学行为的影响；电镜扫描根际土壤和根系，了解在根际土壤中是否产生磷酸镉沉淀影响土壤镉的植物有效性。研究将为生产应用磷肥改良与修复镉污染稻田提供科学依据。

本项目在分析不同磷肥及其施用量下水稻不同部位Cd累积变化的基础上，进一步分析土壤根际效应、根表铁膜数量以及根系分泌物对土壤Cd化学行为的影响，同时还研究了不同施磷量下稻田磷的流失风险。项目主要研究结果如下：.1）水稻Cd含量根系最高、秸秆次之，稻壳和稻米较低。不同磷肥及施磷量对水稻不同部位Cd含量及累积量的影响因稻季、水稻生育期及土壤性质的不同而不同。.2）根际与非根际土壤性质有明显差异，有效Cd含量根际土壤显著低于非根际土壤，其与成熟期水稻Cd含量及累积量的关系均呈一元二次方程式关系。其中钙镁磷肥、过磷酸钙、磷酸二氢铵、磷酸二氢钾处理为开口向下的抛物线，即随根际土壤有效Cd含量的增加先增加后下降，而磷酸二氢钙和复合肥处理则随根际土壤有效Cd含量的增加先下降后增加。不同磷肥处理下，土壤有效Cd含量与有效Cu、Zn、Fe、Mn和Mg含量关系也差异显著。.3）不同磷肥处理下根际土壤对Cd的吸附量均随施磷水平的增加先增加后下降，以0.4 P2O5 kg-1施磷水平吸附量达到最大值；而Cd的解吸量随施磷水平的增加而下降，不同施磷处理下土壤Cd的解吸量无显著差异。.4）根表铁膜的数量及其Cd含量因磷肥的不同而不同，但根表铁膜的数量均与其Cd含量呈显著正相关关系，也与秸秆、根系、稻壳和稻米Cd含量呈正相关关系（除了钙镁磷肥与磷酸二氢铵处理）。.5）根系分泌物可提高土壤对Cd的吸附及降低透析袋外溶液Cd浓度，但对土壤Cd的溶解度无显著影响。不同磷肥、不同施磷量下水稻根系分泌物对Cd的吸附、络合有差异，但对Cd的溶解度无显著差异。.6）2-4倍增量施磷对水稻不仅无增产优势，且不同程度提高水稻地上部磷素累积量、土壤表观磷素盈余量和Olsen-P含量，降低磷肥利用率，显著增加田面水磷浓度，磷流失环境风险高。.7）发表研究论文3篇，其中2篇SCI，1篇一级中文核心。申请专利3项。