DataSheet1_Vertical distribution and transformation of phosphorus and iron in paddy soils during the whole growth stage of rice.docx

Paddy fields have alternating wet and dry hydrological cycles at different growth stages of rice, driving changes in soil environment and phosphorus (P) transformation and transport. In-situ measurements of dissolved oxygen (DO), iron (Fe), and P concentrations were conducted to determine the vertical distribution of these concentrations together with the hydrological and meteorological data during the whole growth stage. The results demonstrate that soil vertical DO concentrations at different growth stages were greatly influenced by the water level and temperature of the paddy field at the soil-water interface. A strong negative correlation between soil DO and DGT-labile Fe has been observed, whereas a strong positive correlation has been observed between soil Fe concentration and vertical P. In the paddy field, soil DO concentrations were lower during tillering, booting, and heading to flowering than during the other stages. Thus, soluble P fluxes from soil water interfaces (SWIs) to overlying waters were most significant during these three stages. Furthermore, soils in these three stages are capable of sustained release of P and are highly able to buffer P. Consequently, water management in paddy fields should take into account the hydrological environment during these three stages in order to minimize soil P release. The results of our study provide a valuable reference point for controlling soil P and Fe during rice growth.

水稻不同生育期的稻田呈现干湿交替的水文循环过程，进而驱动土壤环境及磷（P）的转化与迁移。本研究通过原位测定溶解氧(DO)、铁(Fe)及磷浓度，结合全生育期的水文与气象数据，明确了上述物质的垂直分布特征。结果显示，不同生育期土壤垂直溶解氧浓度主要受土水界面处稻田水位与水温的显著影响。研究观测到土壤溶解氧与扩散梯度凝胶(DGT)可提取态铁之间存在显著负相关关系，而土壤铁浓度与垂直分布的磷则呈显著正相关。稻田土壤在分蘖期、孕穗期及抽穗开花期的溶解氧浓度均低于其余生育阶段，故此土水界面(SWIs)处可溶性磷向上覆水的迁移通量在上述三个生育期最为显著。此外，该三个生育期的土壤可实现磷的持续释放，且具备较强的磷缓冲能力。因此，稻田水分管理需兼顾该三个生育期的水文环境，以最大限度抑制土壤磷的释放。本研究结果可为水稻生育期内土壤磷与铁的调控提供重要参考依据。