颗粒有机质对紫色水稻土镉迁移转化及有效性的影响及机制

Rice, as a major staple food crop in China, is liable to accumulate cadmium. Purple paddy soil is playing an important role in rice production in China, especially in Sichun basin. Soil organic matter has been reported as one of the most important factors influencing the transformation, mobility and bioavailability of cadmium in soils.However, the influence depends on the types of soils and the properties of organic matters. Particulate organic matter (POM), consisting of light-density, sand-sized organic debris with relative rapid turnover, is a key fraction of organic matter influencing soil fertility. Recently, researchers found that a significant metal enrichment in POM compared to the other soil constituents. This result give us a hint that POM play an important role in metal accumulation in soils. However, the effect of POM on the transformation and bioavailability of cadmium in soil is not clear. The aims of this project are: 1) to investigate the characteristics and mechanisms of cadmium enrichment on POM in the purple paddy soil using the combiantuon methods of particle size fractionation, fourier transform infrared spectroscopy and nuclear magnetic resonance imaging; 2) to study the effect of POM on the transformation of cadmium in soils and its relationship with the mineralization of POM through adsorption-desorption experiments and soil incubation; 3) to study the impact of POM on cadmium uptake by rice and its relationship with the changes of soil properties caused by the addition of POM and different types of organic amendments by several sets of pot experiments; 4) to clarify the influences of methods of fertilization and tillage practices on cadmium uptake by rice and the role of POM through long-term field experiments. In addition, scanning electron micrographs, fourier transform infrared spectroscopy and nuclear magnetic resonance imaging, were employed to elucidate the binding sites and coordination environment of cadmium ions on POM. The results can help us further understand the effect of organic matter on the transformation of cadmium in soil and assess its potential in remediation of cadmium-polluted purple paddy soil.

水稻是我国重要的粮食作物，对镉有较强的富集能力，紫色水稻土是我国重要的水稻土资源。有机质是影响土壤镉迁移转化及生物有效性的重要因素，颗粒有机质(POM)是土壤中活性高、周转快的有机质组分，在有机质功能中起着关键作用。研究发现，土壤POM对重金属有明显富集作用，但其对土壤镉的迁移转化行为及有效性的影响还不清楚。项目采用颗粒分组结合红外光谱、核磁共振技术研究紫色水稻土POM的性质及其对镉的富集特征与影响因素；通过吸附解吸试验、培养试验和形态分级法研究POM对紫色水稻土镉迁移转化的影响及其与POM矿化的耦合关系；通过盆栽试验研究POM对水稻镉吸收的影响及其与POM引起的土壤性质变化的关系；通过盆栽试验和长期定位试验研究不同有机物料和施肥模式、耕作方式下POM在水稻镉吸收中的调控作用。结果对阐明有机质与镉的作用机制，全面了解镉的生物地球化学行为及生物效应和修复治理镉污染紫色水稻土具有重要意义。

水稻是我国重要的粮食作物，对镉有较强的富集能力，紫色水稻土是我国重要的水稻土资源。颗粒有机质(POM)是土壤中活性高、周转快的有机质组分，在有机质功能中起着关键作用。研究发现，POM对重金属有明显富集作用，但其对土壤镉的迁移转化行为及有效性的影响还不清楚。本项目研究表明，紫色水稻土POM含量在0.44%~9.68%，尽管其数量不多，但POM-C代表了大部分土壤有机碳库。POM-C对有机碳和Cd有一定的富集能力，其对土壤SOC和Cd的贡献随粒径的减小而增大，且因母质的不同而异，POM-C总量是影响POM-Cd总量的主要因素。POM对对Cd的吸附主要通过表面有机官能团的络合作用完成，为吸热反应，以表面单层吸附为主。POM在土壤中的分解动态因土壤水分的不同而异，淹水条件下POM的潜在矿化势和分解率更高、半周转期更长，POM含量和POM-Cd含量更高，但矿化速率、POM-C含量更低。盆栽试验结果表明，POM可提高土壤镉的有效性，促进秸秆中镉的积累，但其效果因POM量的提高而降低，POM在添加量较少时抑制Cd从水稻茎叶向籽粒转运，当添加达到一定量时，则促进Cd从茎叶向籽粒转运，最终提高籽粒中Cd含量。施用有机物料可显著提高土壤POM、POM-C含量及POM-Cd富集总量，水稻土Cd的有效性，提高各部位Cd含量，抑制Cd从根向茎叶转运，促进Cd从茎叶向籽粒转运，但其效果因有机物料性质不同而异。田间长期定位试验结果表明，与稻-油轮作相比，水稻-冬水田可提高水稻土POM、POM-C和POM-Cd总量的积累，而POM-C、POM-Cd总量在水稻-冬水田系统中垄作免耕与常规耕作间的差异不显著，稻油轮作下垄作免耕显著提高。耕作方式对油菜镉含量的影响不显著，但稻-油轮作系统较水稻-冬水田系统水稻镉含量更高，所有处理中，水稻镉含量以垄作免耕（稻油轮作）最高，常规耕作（稻油轮作）最低。相关分析表明，水稻茎秆和砻糠中Cd含量与土壤POM-C总量显著相关，糙米Cd含量与土壤POM-Cd总量显著相关。结果对阐明有机质与镉的作用机制，全面了解镉的生物地球化学行为及生物效应和修复治理镉污染紫色水稻土具有重要意义。