水分管理对镉轻度污染农田水稻镉积累的影响

Improving Water Management to Reduce Cd Accumulation in Rice in Lightly Cd-Polluted Paddy Soils

【目的】研究镉轻度污染农田水稻适宜的水分管理模式。【方法】采用盆栽试验,分别设置水稻全生育期湿润灌溉(CK)、全生育期淹水(T1)、拔节期(T2)、孕穗期(T3)、抽穗扬花期(T4)、灌浆乳熟期(T5)、蜡熟期(T6)开始淹水7个处理,对水稻不同器官镉积累差异以及土壤氧化还原电位、根际土壤溶液水溶性镉质量分数变化进行研究。【结果】土壤氧化还原电位与水溶性Cd呈极显著正相关(p<0.01),淹水后土壤的氧化还原电位(Eh)显著降低,土壤还原性增强,淹水时间越长氧化还原电位越低,其中T1处理最低可降至-159.78mV,淹水后根际土壤溶液中水溶性Cd也迅速下降,T3处理下降最多,为75.0%。不同水分管理模式下水稻糙米含镉量均未超过食品安全国家标准规定的限量值(GB2762—2017)。与CK相比,T1处理降低稻米含镉量达76.9%,而水稻产量明显下降,减产19.2%;T6处理明显抑制镉从水稻根系向地上部分转移,增加根系镉质量占比15.2%;T6处理降低水稻茎秆的镉积累,降低茎秆镉质量占比13.0%;淹水通过抑制镉从水稻叶片向谷物的转移来降低稻米镉积累,与CK相比,T5处理叶片镉质量占比增加5.0%,T3处理谷物镉质量占比降低4.3%。【结论】综合考虑水稻产量、稻米含镉量和田间农事操作习惯,镉轻度污染稻田推荐的水分调控方式为抽穗扬花期淹水至收获前1周。

【Background】Soil pollution by cadmium has become an increasing concern not only because of its toxicity after entering the food chain but also due to its detrimental impact on soil quality and developing sustainable agriculture.As all biogeochemical processes controlling Cd bioavailability in soil are modulated by soil moisture,we conjecture that improving water management should be able to immobilize Cd and reduce its root uptake and translocation in crop.【Objective】The purpose of this paper is to experimentally explore the appropriate water management to reduce Cd uptake and translocation in rice grownin lightly Cd-polluted paddy soils.【Method】The experiment was conducted in pots and consisted of seven treatments:Keeping the soil moist at a predefined level during the whole growth season(CK);keeping the pot flooded during the whole growth season(T1),flooding from the stem elongation stage onwards(T2),flooding from the panicle initiation to booting stage onwards(T3),flooding from the heading and flowering stage onwards(T4),flooding from milk grain stage onwards(T5),and flooding from dough grain stage onwards(T6).All treatments were drained one week before harvest.In each treatment,we measured Cd accumulation in different plant tissues,as well as the changes in redox potential and soluble Cd in the rhizosphere.【Result】Both redox potential and soluble Cd in soil were positively correlated at significant level(p<0.01).Both redox potential and soluble Cd in soil dropped steadily after flooding,making the soil more reductive.The longer the flooding lasted,the lower the redox potential was.The redox potential in T1 could drop as low as-159.78 mV,and T3 reduced the soluble Cd in the rhizosphere by 75.0%.The cadmium content in the rice grains did not exceed the criterion set in the national food safety standard(GB2762—2017)regardless of the treatments.Compared with CK,T1 reduced Cd content in the rice by 76.9%while in the meantime increasing rice yield by 19.2%.T6 impeded Cd translocation from the roots to the shoots,by increasing the Cd fraction in the roots by 15.2%and reducing the Cd accumulation in the stems by 13.0%.On average,flooding impeded Cd translocation from leaves to grains.Compared with CK,T5 increased the fraction of Cd in leaves by 5.0%while T3 reduced the fraction of Cd in grains by 4.3%.【Conclusion】Considering the balance of yield,Cd content in grain and ease of implementation,the best water management for the lightly Cd-contaminated paddy soils was to flood the fields from the heading and flowering stage until one week prior to the harvest.