Minerals are known to protect dissolved organic matter (DOM) against biodegradation and thus play an important role in the long-term persistence of organic carbon (OC) in soils. However, as a super-mixture of organic compounds, it is expected that not all components in DOM can be protected by minerals due to selective adsorption. The present study examined how molecular fractionation of plant-derived DOM at ferrihydrite–water interface affects their biodegradation. The results of Fourier transform ion cyclotron resonance mass spectrometry analysis showed that highly unsaturated and oxygenated moieties in DOM displayed high affinities, while highly saturated compounds rich in aliphatic groups exhibited low affinities to ferrihydrite, resulting in the molecular fractionation of DOM at the water–mineral interface. Comparison of the biodegradation of DOM extracted from different phases after adsorption on ferrihydrite indicated that compounds with lower affinities to ferrihydrite had higher degradation degrees, while compounds with higher affinities to ferrihydrite had lower degradation degrees. Considering the protective role of minerals on adsorbed OC, molecular fractionation at the ferrihydrite–water interface leads to inherently refractory OC being more stable, while labile OC is more easily degraded in soils.

中文翻译：

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界面分子分级诱导水铁矿对生物耐火有机物的优先保护

众所周知，矿物质可保护溶解的有机物（DOM）免受生物降解，因此在土壤中有机碳（OC）的长期残留中起着重要的作用。但是，作为有机化合物的超混合物，预计由于选择性吸附，并非DOM中的所有成分都可以被矿物质保护。本研究研究了在水铁矿-水界面处植物来源的DOM的分子分级分离如何影响其生物降解。傅里叶变换离子回旋共振质谱分析的结果表明，DOM中的高度不饱和和含氧部分显示出高亲和力，而富含脂肪族基团的高度饱和的化合物则显示出对水铁矿的低亲和力，从而导致DOM在水矿物上的分子分馏界面。比较吸附在三水铁矿上的不同相提取的DOM的生物降解结果表明，对三水铁矿的亲和力较低的化合物具有较高的降解度，而对三水铁矿的亲和力较高的化合物具有较低的降解度。考虑到矿物对吸附的OC的保护作用，水铁矿-水界面的分子分馏导致固有的难熔OC更稳定，而不稳定的OC在土壤中更容易降解。