秸秆还田对土壤稀土元素生物有效性及环境效应的影响

The region of South China with Jiangxi province as the center is the world'slargest rare earth mining area of ionic type, the farmland has serious pollutionof rare earth because of mineral exploitation, this region is also the most important rice production area in China. Annual production of hundreds of millions of tons of straw returns to the field basically，while,key functional genes is not clear the effect of straw incorporation on the accumulation of rare earth elements in rice and the ecological environment of paddy field.Through the experiment of potted rice in greenhouse, laboratory experiment and field experiment in mining area, we use technology of three dimensional fluorescence spectroscopy and model of fluorescence quenching to characterize straw composting process and the interaction of maturity with rare earth, use Raman spectroscopy and field emission.scanning electron microscopy together to explain effect of silicon on the absorption and accumulation of rare earth elements in Rice; use Quantitative PCR and high throughput sequencing of illumina MiSeq to characterize environmental responses of soil microbes and endophytic bacteria in tunnel after returning different amount of straw to soil. And finally clarify the mechanism and effect of straw incorporation on rice yield, quality and ecological environment in the rare earth mining area, and put forward reasonable amount of straw in rare earth mining area.The research results have important theoretical and practical significance to guide the safety of food production and environmental protection in the mining area.

以江西为中心的中国南方地区是世界最大的离子型稀土矿区，因矿产开采，农田稀土污染严重。该区也是中国最重要的水稻生产区，每年产生几亿吨的秸秆基本还田。然而，秸秆还田对稀土元素在水稻中的积累及稻田生态环境影响的关键因子尚不清楚。通过温室盆栽水稻、实验室培养验和矿区稻田试验，利用三维荧光光谱技术和荧光猝灭模型表征秸秆的腐解过程及腐解物与稀土的相互作用，将拉曼光谱与场发射扫描电镜联用诠释硅对水稻吸收积累稀土元素的影响，采用定量PCR与illumina MiSeq高通量测序表征不同秸秆量还田后土壤微生物及水稻内生菌的环境响应及作用机制。最终阐明不同秸秆量还田对稀土矿区水稻产量与质量及生态环境的影响，提出稀土矿区秸秆还田的合理方式。研究成果对指导矿区粮食安全生产和环境保护具有重要的理论和实践意义。

实验室培养实验表明，1%和2%的秸秆还田增加了土壤全P、全N、铵态氮、速效钾、pH及有机质的积累，2%的秸秆还田增加更为明显，分别平均增加了11.2%、8.5%、12.3%、51.6%、12.2%、4.2%。盆栽实验表明，单纯的秸秆还田均提高了土壤pH及K等的含量，1%和2%的秸秆还田均降低了水稻根、茎叶和籽粒的干重，2%的秸秆还田降低更为显著，降低量在10-30%之间；秸秆还田均提高了水稻稀土元素含量，2%的秸秆还田提高量大于1%的秸秆还田；水稻分蘖期秸秆不同的还田量和施肥方式提高了根内菌、根际菌的chao1指数，根内菌增幅在47.9%-97.2%之间，根际菌增幅在5.6%-25.4%之间；成熟期秸秆不同的还田方式均降低了水稻根内菌chao1指数，降幅在6.1%-30.8%之间；分蘖期秸秆不同的还田方式均显著提高了水稻根内、根际菌Richness指数，增幅在125.1%-166.8%之间，成熟期秸秆还田提高了水稻根内菌的Richness指数，增幅在11.4%-62.3%之间；2%的秸秆还田提高了Acidovorax、Clostridium sensu stricto、Citrobacter、Curtobacterium等有害菌、致病菌的丰度，1%秸秆还田促进了Lactobacillus、Azospira、Acinetobacter、Bradyrhizobium、Acidocella等固氮、促生、抗胁迫菌的丰度；2%秸秆还田促进了有害菌的形成，这可能是其导致水稻籽粒干重显著降低的重要原因。大田实验表明，1%的秸秆与常规用量的P、K及常规用量1.2倍的N费配施或者1%的秸秆与常规用量的N、P、K及动物粪便混合还田土壤中的N、P、K含量有所提高，土壤pH略有提升，土壤中有益菌多样性和丰富度有所提高，水稻籽粒干重分别增加了21.1%、27.0%，稀土含量分别降低了17.3%、29.3%。通过三维荧光光谱技术和荧光猝灭模型表征秸秆的腐解过程及腐解物与稀土元素Ce的相互作用，结果表明Ce与腐解物形成了有机络合物，从而影响土壤稀土元素生物有效性及环境效应。研究认为，1%的秸秆与常规用量的P、K及常规用量1.2倍的N肥配施或者1%的秸秆与常规用量的N、P、K及动物粪便混合还田，能有效促进稀土矿区居民的粮食安全和生态环境保护。