不同生育期施加超细磷矿粉对水稻吸收和转运Pb、Cd的影响

为了探究水稻不同生育期施加超细磷矿粉(100 nm)对Pb-Cd污染土壤Pb、Cd吸收和转运的影响,采用盆栽试验,研究了插秧前、分蘖期和扬花期施加不同用量的超细磷矿粉对水稻稻谷产量,植株Pb、Cd的吸收转运及对土壤中Pb、Cd形态的影响。结果表明,不同生育期施加超细磷矿粉的水稻稻谷产量增加了9.70%～26.60%,显著高于对照和普通磷矿粉处理。水稻根、茎叶、稻壳和稻米中Pb、Cd含量均随超细磷矿粉用量的增加而降低。插秧前施加超细磷矿粉稻米中Pb含量显著低于对照(75.7%～79.1%)和普通磷矿粉处理(73.5%～77.3%),降低效果好于分蘖期(51.4%～69.1%)和扬花期(51.9%～61.5%);而扬花期施加稻米中Cd含量显著低于对照处理(44.3%～71.9%)和普通磷矿粉处理(44.1%～71.8%),降低效果好于插秧前(32.7%～45.8%)和分蘖期(28.2%～39.9%)。施加超细磷矿粉后稻米中Pb、Cd含量大部分低于国家食品的限量卫生标准GB 2762—2017(≤0.2 mg·kg-1)。扬花期施加超细磷矿粉降低土壤交换态Cd的效果(16.8%～33.4%)好于插秧前(18.0%～27.8%)和分蘖期(11.8%～27.9%),插秧前施加超细磷矿粉降低土壤交换态Pb的效果(143.8%～193.3%)好于分蘖期(103.2%～183.4%)和扬花期(56.0%～160.6%)。土壤中交换态Cd、Pb含量与稻米中Cd、Pb含量呈显著正相关,相关系数分别达0.856和0.946。水稻Cd、Pb的吸收系数和初级转运系数均随超细磷矿粉用量的增加而降低,与对照差异显著。因此,超细磷矿粉可通过钝化土壤中交换态Pb、Cd,降低水稻对Pb、Cd的吸收转运,并提高稻谷产量。建议超细磷矿粉用量为2 g·kg-1土,单独Pb污染或Cd污染的土壤可分别在种植前或生长旺期施用,而复合污染的土壤在种植前施用综合效果较佳且操作方便。

Effects of superfine phosphate rock powders on Pb and Cd uptake and transportation in rice at different growth stages

This study investigates the effects of the application of superfine phosphate rock powders(SPRP) on the absorption and transfer of lead(Pb) and cadmium(Cd) in soils contaminated with these elements during different growth periods of rice. Pot experiments were carried out to analyze the effects of i) different amount of SPRP on rice yields, ii) the absorption and transportation of Pb and Cd in plants, and iii) the forms of Pb and Cd in soils, when SPRP were applied at the pre-transplanting, tillering, and flowering stages of rice. The results showed that the yields of rice increased by between 9.70% to 26.60% with SPRP application, which were significantly higher than of rice yields with unground powders or without powder treatment. The concentrations of Pb and Cd decreased with increased levels of SPRP in all parts of the rice, including the root, stem, hull, and grain. When SPRP were applied at the pre-transplanting stage, the Pb concentrations of rice grains were between 75.7% to 79.1% lower than of those without any powder, and from between 73.5% to 77.3% lower than of those treated with unground powder. The reduction effects of grain Pb concentrations were better than of those at the tillering stage(55.4%~69.1%) and flowering stage(55.9%~61.5%). The application of SPRP at the flowering stage resulted in the grain Cd concentrations being between 44.3%~71.9% and 44.1%~71.8% lower than of those in the control and unground treatments, respectively. The reduction effects at the flowering stage were better than of those at the pre-transplanting stage(33.0%~45.8%) and tilling stage(28.6%~39.9%). With the application of superfine powders, the Pb and Cd concentrations in grain were mostly lower than the limit of 0.2 mg·kg^-1 defined in the National Food Health Standard(GB 2762-2017). The application stage of SPRP also had a notable influence on exchangeable heavy metals in soils. The concentrations of soil exchangeable Cd were decreased by between 16.8% to 33.4% at flowering stage, which were better than of those at the pre-transplanting stage(18.0%~27.8%) and tillering stage(11.8%~27.9%). Meanwhile, the reductions in concentrations of soil exchangeable Pb ranged from 143.8% to 193.3% at the pre-transplanting stage, which was better than of those at the tillering stage (103.2%~183.4%) and flowering stage(56.0%~160.6%). The concentrations of exchangeable Cd and Pb in soils were positively correlated with their concentrations in rice grains, with correlation coefficients of 0.856 and 0.946, respectively. The absorption and primary transport coefficients of Cd and Pb decreased with increased dosage of SPRP, and were significantly different from those in the control. Therefore, the application of SPRP led to the passivation of the concentrations of exchangeable Pb and Cd in contaminated soils, a gradual reduction in the uptake and transport of heavy metals by rice, and an increase in rice yields. We conclude that the suggested optimum amount of SPRP is 2 g·kg^-1 of polluted soils, which can be applied to soils polluted by Pb or Cd at pre-planting stage or growth boom stage, respectively. For complex soil pollution, we suggest that it is better to apply SPRP before planting in order to achieve improved comprehensive effects and easy operation.