College of Resources and Environment , Huazhong Agricultural University , Wuhan 430070 , China.
Institut für Mineralogie , University of Münster , 48149 Münster , Germany.
Environ Sci Technol. 2019 Jul 16;53(14):8097-8104. doi: 10.1021/acs.est.8b06807. Epub 2019 Jun 26.
Global soil carbon cycling plays a key role in regulating and stabilizing the earth's climate change because of soils with amounts of carbon at least three times greater than those of other ecological systems. Soil minerals have also been shown to underlie the persistence of soil organic matter (SOM) through both adsorption and occlusion, but the microscopic mechanisms that control the latter process are poorly understood. Here, using time-resolved in situ atomic force microscopy (AFM) to observe how calcite, a representative mineral in alkaline soils, interacts with humic substances, we show that following adsorption, humic substances are gradually occluded by the advancing steps of spirals on the calcite (1014) face grown in relatively high supersaturated solutions, through the embedment, compression, and closure of humic substance particles into cavities. This occlusion progress is inhibited by phytate at high concentrations (10-100 μM) due to the formation of phytate-Ca precipitates on step edges to prevent the step advancement, whereas phytate at relatively low concentrations (≤1 μM) and oxalate at high concentrations (100 μM) have little effect on this process. These in situ observations may provide new insights into the organo-mineral interaction, resulting in the incorporation of humic substances into minerals with a longer storage time to delay degradation in soils. This will improve our understanding of carbon cycling and immobilization in soil ecological systems.
全球土壤碳循环在调节和稳定地球气候变化方面起着关键作用，因为土壤中的碳含量至少是其他生态系统的三倍。土壤矿物质也通过吸附和固持作用，为土壤有机质（SOM）的持久性提供了基础，但控制后者过程的微观机制还知之甚少。在这里，我们使用时间分辨的原子力显微镜（AFM）来观察方解石（一种碱性土壤中的代表性矿物）与腐殖质物质的相互作用，结果表明，在吸附之后，腐殖质物质逐渐被在相对高过饱和度溶液中生长的方解石（1014）面上螺旋形突起的推进步骤所固持，通过嵌入、压缩和将腐殖质颗粒封闭到空洞中。由于在台阶边缘形成植酸钙沉淀，从而阻止了台阶的推进，高浓度（10-100 μM）的植酸盐会抑制这种固持过程；而相对低浓度（≤1 μM）的植酸盐和高浓度（100 μM）的草酸盐对此过程几乎没有影响。这些原位观察结果可能为有机-矿物相互作用提供新的见解，导致腐殖质物质被纳入矿物中，从而具有更长的储存时间，以延迟土壤中的降解。这将提高我们对土壤生态系统中碳循环和固定的理解。
