稻田亚铁氧化对硝酸盐还原过程N2O排放的调控机制

Nitrate reduction makes a significant contribution to N2O emissions from flooded paddy soils. Iron is the fourth abundant metal element in the Earth’s crust. The process of Fe(II) oxidation coupled to nitrate reduction readily occurs in flooded paddy soils. Nevertheless, few studies have concentrated on the effect of iron on N2O emissions. Moreover, little knowledge has been claimed about the individual contributions of chemical and biological reactions in the coupling process of Fe(II) oxidation and nitrate reduction to N2O emissions. Therefore, in this project the flooded anoxic paddy soils will be taken as the research object; the effects of the concentrations, morphologies and mineral crystal types of Fe(II) on chemodenitrification in the sterilized soils will be analyzed to explore the chemical mechanism of N2O emission regulated by Fe(II) oxidation; the abundance of nitrogen function genes related to nitrate reduction process will be determined to uncover the biological mechanism of N2O emission regulated by Fe(II) oxidation; the fate of nitrogen in the Fe(II)-nitrate coupling process will be tracked by introducing the stable isotope, and N2O emissions from nitrate reduction in sterilized and non-sterilized soils will be distinguished by nitrogen and oxygen isotopic fractionation and N2O site preference to quantatively evaluate the contributions of abiotic and biotic reactions in Fe(II)-nitrate coupling process to N2O emissions. This study can further illuminate the process of Fe(II) oxidation coupled to nitrate reduction in paddy soils, reveal the mechanism of N2O emissions regulated by the coupling process, and is of great significance to soil chemistry and environmental science.

硝酸盐还原过程对淹水稻田土壤的N2O排放有着重要贡献。铁是地壳中含量排名第四的金属元素，亚铁氧化耦合硝酸盐还原过程很容易发生淹水稻田土壤中。然而，极少有研究关注铁对硝酸盐还原过程N2O排放的影响，而且亚铁-硝酸盐耦合过程中化学和生物反应对N2O排放的贡献尚无可知。因此，本项目将以淹水厌氧稻田土壤为模式体系，通过分析灭菌土壤中亚铁浓度、溶解性和矿物晶型对化学反硝化的影响来探究亚铁氧化对N2O排放的化学调控机制；结合硝酸盐还原氮功能基因数据深入解析亚铁氧化对N2O排放的微生物调控机制；引入稳定性同位素标记追踪亚铁-硝酸盐耦合过程中氮的去向，借助氮氧同位素分馏和N2O位点偏好分析来定量评估亚铁-硝酸盐耦合过程中化学和生物反应对N2O排放的相应贡献。该研究可深入阐明稻田土壤中亚铁氧化-硝酸盐还原的耦合过程，并揭示其对N2O排放的调控机制，具有重要的土壤化学与环境科学意义。

硝酸盐还原过程对稻田土壤的N2O排放有着重要贡献，亚铁氧化耦合硝酸盐还原过程很容易发生淹水稻田土壤中。然而，亚铁对硝酸盐还原过程N2O排放的化学和生物调控机制尚不清楚。本项目以淹水厌氧稻田土壤为模式体系，通过灭菌和非灭菌对照处理，结合动力学过程研究和微生物多样性分析，探究亚铁对硝酸盐还原过程N2O排放的化学和生物调控机制。主要研究结果有：.（1）在厌氧稻田土壤中，添加亚铁加速了硝酸盐的还原消耗，增加了亚硝酸盐累积，同时促进了硝酸盐还原过程的N2O排放，暗示亚铁可通过调节硝酸盐还原过程的生物反应和化学反应来影响土壤的N2O排放。.（2）在灭菌土壤中，亚铁不能被硝酸盐化学氧化，但亚铁可与亚硝酸盐发生快速的氧化还原反应，即亚铁诱发了化学反硝化过程的发生，同时生成N2O。高浓度亚铁提高了化学反硝化过程的N2O排放。.（3）高铁土壤的nosZ基因丰度显著低于低铁土壤的nosZ基因丰度，且外源亚铁降低了低铁土壤的nosZ基因丰度，暗示着高含量亚铁可能会抑制nosZ基因微生物的生长繁殖。添加亚铁使土壤硝酸盐还原过程的优势菌目RBG-13-54-9、Isosphaerales和Ktedonobacterales得到了明显富集。.（4）在低有机碳土壤中，亚铁氧化耦合硝酸盐还原过程的化学和生物反应对N2O排放的贡献分别是6.8%和93.2%；在高有机碳土壤中，其化学和生物反应对N2O排放的贡献分别为67.6%和32.4%。.（5）硝酸盐还原耦合亚铁氧化反应可影响土壤铁形态转化。添加硝态氮降低了土壤离子交换态铁含量，但对有机结合态铁含量无影响。亚铁氧化耦合硝酸盐还原反应增加了低有机碳土壤残渣态铁含量，但在高有机碳土壤中无影响。.本研究为土壤铁氮耦合研究提供理论依据，从铁这一视角为调控稻田土壤N2O排放提供了新的研究思路，亚铁氧化耦合硝酸盐还原引起的土壤铁形态转化对研究土壤碳氮周转和污染物迁移具有重要意义。.