非稳态pe+pH水稻土中硫对镉形态与有效性的影响机理

The forms and its effectiveness of sulfur (S) are important factors affecting the uptake and accumulation of Cd by rice cultivars in paddy soils, however, contradictions still exist about the effect of sulfur on the uptake and translocation of Cd by rice plants in paddy soils, which may be related to the unclear mechanisms about the transfer of S forms and thereafter its influence on uptake of Cd by rice plants in paddy soils with unstable pe+pH conditions. Several kinds of paddy soils with various soil properties will be selected for study for this project, typical scenarios of paddy soils with unstable pe+pH condition (strong reduction in seedling stage, oxygen secretion by root, flooding and dry and wet alternation) will be simulated, and root box culture experiment, soil incubation and pot experiment will be conducted combined with the in-situ determination technology of Eh and pH value in soils, SEM/TEM-EDS and PCR measure technology to study: 1) the relationship between morphological transformation of S and pe+pH in rhizosphere/non rhizosphere paddy soils; 2) the effects of the forms of iron oxides and community of S reducing bacteria (SRB) on the morphology of S in soils; 3) the effects of soil properties on the morphology of S transformation and its prediction model; 4) the influence of forms of S on the microstructure of root surface of rice plants and their relationship with Cd uptake and its translocation in plants in rhizosphere/non rhizosphere soil. Through the above study, this project intends to reveal theoretical basis for the study of effect of S on the uptake and transformation of Cd by rice cultivars under unstable pe+pH conditions in paddy soils.

稻田土壤中硫（S）的形态与有效性是影响水稻吸收Cd的一个重要因子，但目前关于稻田土壤中S影响水稻Cd吸收的研究结果存在矛盾之处，这可能与非稳态pe+pH条件下水稻根际土壤S的形态转化驱动机制及S形态介导下Cd有效性变化机理不清有关。本项目拟选择不同性质水稻土，根据稻田土壤不同pe+pH情景（幼苗期强还原、根系泌氧、淹水及干湿交替），利用根箱、土培及盆栽试验，结合土壤Eh、pH原位测定、SEM/TEM-EDS测定及PCR扩增技术等，研究稻田土壤非稳态pe+pH条件下：1）水稻根际/非根际土壤中S形态转化及其与pe+pH量化关系；2）土壤中铁氧化物及S还原菌（SRB）群落变化对S形态转化影响；3）土壤性质对S形态转化影响及其预测模型；4）根际S形态对水稻根表微观结构影响及其与水稻根系吸收、转运Cd关系。通过上述研究，为揭示非稳态pe+pH下稻田土壤中S对水稻Cd吸收、转化影响机理。

本项目选择了不同性质水稻土，根据稻田土不同pe+pH情景，利用根箱、土培及盆栽试验，结合土壤Eh、pH原位测定、SEM/TEM-EDS测定及PCR扩增技术等，研究了稻田土壤非稳态pe+pH条件下，水稻根际/非根际土壤中S形态转化及其与pe+pH量化关系；土壤中铁氧化物及S还原菌（SRB）群落变化对S形态转化的影响机制；土壤性质对S形态转化影响及其预测模型；根际S形态对水稻根表微观结构影响及其与水稻根系吸收、转运Cd关系。主要结果包括：1）探明了不同生育期水稻根际土壤pe+pH变化对S、Cd形态变化及Cd有效性的影响： S对分蘖期、抽穗期和成熟期水稻Cd积累具有显著降低作用，不同浓度S处理显著提高水稻根系中谷胱甘肽（GSH）、非蛋白巯基（NPT）和植物螯合态（PCs）的含量；2）揭示了非稳态pe+pH条件下土壤中S、铁氧化物及Cd形态转化的耦合关系：土壤S供应水平与铁膜中的Fe浓度之间存在显著的正相关关系，S的添加会促进根表铁膜的形成，S诱导铁膜形成增强了根系表面对Cd的隔离，进而降低了水稻根系对Cd的吸收。3）探明了不同pe+pH条件下水稻土微生物群落变化对S、Cd形态转化的微生物机制：在施S处理下，根际土壤Cd有效态显著降低；随着pe+pH值下降，土壤中厌气菌如Bacteroidia相对丰度会不同程度的增加，而好氧细菌如硫还原菌Desulfobacterota 、Planctomyces相对丰度减少，同时，土壤中嗜酸菌如Acidobacteria的相对丰度会增加；4）揭示了非稳态pe+pH条件下S对水稻根表微观结构影响及其与水稻Cd转运机制：施S处理土壤中，pe+pH变化影响水稻根表胶膜的形成，从而影响水稻根系对土壤Cd的吸附、转运，其中pe+pH在6~9范围有利于根表铁膜的形成。上述结果对进一步认识非稳态pe+pH下稻田土壤中S对水稻Cd吸收、转化的影响提供了理论依据。