posted on 2019-06-17, 00:00authored byJialin Chi, Wenjun Zhang, Lijun Wang, Christine V. Putnis
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.