不同水分管理对贵州喀斯特山区水稻土镉形态及水稻镉积累的影响机制

Cadmium (Cd)is a major contaminating heavy metal with highly active chemical behaviors and mobility in the agricultural soil. With the development of industry, Cd pollution becomes more and more serious, and has seriously threatened the agricultural production and human health through the food chain.Therefore,people have paid close attention to its behaviors in environment.The water status could affect its environmental chemical behaviors and the absorption and accumulation in plants. Rice is one of the most important field crops in China. Cd pollution is serious in paddy soils. However, there is little research on the effcet of different water regime on Cd chemical behaviors.In the project, based on room culture and pot experiment,we will investigate the characteristics of Cd speciation and transformation in paddy soil in karst mountainous areas of Guizhou province and the tempral and spatial dynamics of Cd in the soil,rhizosphere and different part of rice plant under different water regimes using modern molecular ecology and rhizosphere techniques.Further, We investigate the rhizosphere mechanism on Cd migration and transformation under different water regimes from the aspects of soil pH,Eh, iron plaque,microbial diversity etc.It would be helpfulto discover the mechenism of Cd accumilation in rice under different water regimes and understand the Cd biogeochemical processes.It could provide theoretical basis and practical instruction for controlling Cd transferation along food chain and soil remediation.

镉作为稻田土壤中化学行为活跃和移动性较强的污染元素，在土壤-植物系统和食物链中的传递对人体健康构成的威胁已不容忽视。水分能影响土壤中镉的环境化学行为和植物对镉的吸收积累。然而，目前有关不同水分管理对水稻土中镉形态转化及生物有效性的研究甚少。本研究拟通过室内培养试验和根袋盆栽试验，运用现代分子生态学和根际研究法等技术，研究不同水分管理模式下贵州喀斯特山区水稻土中镉的形态转化特征、土壤-根表铁膜-水稻体系中镉迁移转化规律，从土壤pH、Eh、根表铁膜形成、微生物群落结构等方面探索不同水分管理影响镉迁移转化的根际机制，揭示不同水分管理对水稻积累镉的作用机制，最终系统诠释镉的生物地球化学过程，从而为进一步有效控制污染土壤镉的食物链传递及土壤修复提供理论依据和实践指导。

镉在土壤-水稻系统和食物链中的传递对人体健康构成的威胁已不容忽视。水分能影响土壤中镉的环境化学行为和植物对镉的吸收积累。本研究拟通过室内培养试验和盆栽试验，明确了不同水分管理模式下贵州喀斯特山区水稻土中镉的pH、Eh及形态转化特征，发现75%田间持水量能提高培养期间土壤Eh、降低pH，促进可氧化态镉向酸提取态镉的转化，从而提高镉的有效性。明确了不同水分管理下土壤-根表铁膜-水稻体系中镉迁移转化规律，发现随着水稻生长发育的进行，有效镉含量总体下降，干湿交替灌溉和湿润灌溉能不同程度的提高酸提取态和可还原态镉的含量，促进镉在土壤-水稻植株系统中的转移，增加水稻籽粒中镉的含量，特别是湿润灌溉；干湿交替灌溉和湿润灌溉提高了土壤pH值；显著降低了土壤Eh值；低浓度的镉胁迫下，干湿交替灌溉和湿润灌溉处理的土壤微生物量碳、氮含量在分蘖期、孕穗期和成熟期低于淹水灌溉，高浓度的镉胁迫下，干湿交替灌溉和湿润灌溉处理的土壤微生物量碳、氮含量高于淹水灌溉。不同水分管理对水稻形成铁膜的影响不同，淹水处理时水稻根系铁膜形成呈“先升后降”的趋势，干湿交替处理相比淹水处理形成的水稻根表铁膜数量较多，湿润处理呈现出逐渐下降趋势；干湿交替和湿润灌溉处理相比淹水处理，能提高铁氧化菌的数量，但使铁还原菌数量降低；铁诱导下对水稻根系、茎叶、糙米的镉积累含量均有所降低。明确了不同水分管理对镉污染下水稻叶片蒸腾强度和气孔导度的影响，发现湿润灌溉能明显降低水稻不同生育期叶片气孔导度和蒸腾强度。明确了硝态氮对水稻镉积累的作用，发现硝态氮处理能促进镉由土壤向水稻植株转移。这些结果有利于揭示不同水分管理对水稻镉积累的作用机制，在低镉污染稻田可采用干湿交替灌溉。