Ministry of Education's Key Laboratory of Poyang Lake Wetland and Watershed Research, School of Geography and Environment, Jiangxi Normal University, Nanchang 330022, China; State Key Laboratory of Soil & Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
Ministry of Education's Key Laboratory of Poyang Lake Wetland and Watershed Research, School of Geography and Environment, Jiangxi Normal University, Nanchang 330022, China.
Sci Total Environ. 2024 Oct 10;946:174500. doi: 10.1016/j.scitotenv.2024.174500. Epub 2024 Jul 5.
Paddy drainage is the critical period for rice grain to accumulate cadmium (Cd), however, its roles on spatial heterogeneity of grain Cd within individual fields are still unknown. Herein, field plot experiments were conducted to study the spatial variations of rice Cd under continuous and intermittent (drainage at the tillering or grain-filling or both stages) flooding conditions. The spatial heterogeneity of soil moisture and key factors involved in Cd mobilization during drainages were further investigated to explain grain Cd variation. Rice grain Cd levels under continuous flooding ranged from 0.16 to 0.22 mg kg among nine sampling sites within an individual field. Tillering drainage slightly increased grain Cd levels (0.19-0.31 mg kg) with little change in spatial variation. However, grain-filling drainage greatly increased grain Cd range to 0.33-0.95 mg kg, with a huge spatial variation observed among replicated sites. During two drainage periods, soil moisture decreased variously in different monitoring sites; greater variation (mean values ranged from 0.14 to 0.27 m m) was observed during grain-filling drainage. Accordingly, 2.9-3.3-fold variation in soil Eh and 0.55-0.67-unit variation in soil pH were observed among those sites. In the soil with low moisture, ferrous fractions such as ferrous sulfide (FeS) were prone to be oxidized to ferric fractions; meanwhile, the followed generation of hydroxyl radicals involved in Cd remobilization was enhanced. Consequently, soil dissolved Cd changed from 2.97 to 8.92 μg L among different sampling sites during grain-filling drainage; thus, large variation was observed in grain Cd levels. The findings suggest that grain-filling drainage is the main process controlling spatial variation of grain Cd, which should be paid more attention in paddy Cd evaluation.
排灌是水稻籽粒积累镉（Cd）的关键时期，但它在田间个体籽粒 Cd 空间异质性中的作用仍不清楚。本研究通过田间小区试验，研究了连续和间歇（分蘖期或灌浆期或两者兼排）淹水条件下水稻 Cd 的空间变化。进一步研究了排灌过程中土壤水分的空间变化及其与 Cd 迁移相关的关键因素，以解释籽粒 Cd 的变化。在一个个体田间的 9 个采样点内，连续淹水条件下水稻籽粒 Cd 水平在 0.16-0.22mg/kg 之间。分蘖期排水略微增加了籽粒 Cd 水平（0.19-0.31mg/kg），但空间变异变化不大。然而，灌浆期排水极大地增加了籽粒 Cd 范围至 0.33-0.95mg/kg，在重复采样点之间观察到巨大的空间变异。在两个排水期内，不同监测点的土壤水分以不同的方式下降；在灌浆期排水时，观察到更大的变化（平均值范围为 0.14-0.27mm）。因此，这些站点的土壤 Eh 变化 2.9-3.3 倍，土壤 pH 值变化 0.55-0.67 个单位。在低水分土壤中，二价铁如硫化亚铁（FeS）容易被氧化为三价铁；同时，参与 Cd 再迁移的羟基自由基也随之增加。因此，在灌浆期排水过程中，不同采样点之间的土壤溶解 Cd 从 2.97 变化到 8.92μg/L；因此，籽粒 Cd 水平存在较大差异。研究结果表明，灌浆期排水是控制籽粒 Cd 空间变异的主要过程，在稻田 Cd 评价中应予以更多关注。
