Root Exudates and Microbial Communities Drive Mineral Dissolution and the Formation of Nano-size Minerals in Soils: Implications for Soil Carbon Storage
Mineral binding is a major mechanism for soil carbon (C) stabilization. But the majority of studies represent organo-mineral complexes as “biogeochemical black boxes,” where inputs and outputs of organics and minerals are estimated but the underlying mechanisms controlling C stabilization and storage are rarely explored. Nano-size minerals greatly contribute to C binding and critically affect C storage. Yet, the mechanisms regulating nano-size minerals are poorly understood. Here, root exudates and microbial communities are found to drive mineral dissolution and the formation of nano-size minerals in soils. These neo-formed minerals can contribute to soil C binding. Using three long-term field experiments, organic amendments were found to significantly increase mineral dissolution/availability, particularly of nano-size minerals. Furthermore, the presence of roots significantly increased mineral dissolution/availability and promoted the formation of nano-size minerals. Meanwhile, root exudates promoted the formation of SRO minerals, and that SRO minerals acted as “nuclei” for C retention. Combined Fe redox study and Illumina MiSeq high-throughput sequencing analysis, inorganic and organic fertilization regimes are shown to have contrasting effects on the Fe redox bacterial communities, which then influence Fe cycling in soils and the composition of iron minerals. During Fe(III) reduction, Geobacter were important active Fe(III) reducers, with a higher relative abundance in both organically and inorganically fertilized soils than in no fertilized soils, and their higher abundance was responsible for greater dissolution of ferrihydrite in inorganically fertilized soil than in organically fertilized soil. However, during the Fe(II) oxidation, Pseudomonas and Anaerolinea were more abundant and produced higher levels of poorly crystalline Fe oxides under organic fertilization. Together, these findings indicate that root exudates and microbial communities drive mineral dissolution and the formation of nano-size minerals in soils, which are critical for soil C storage.
We thank Xiangzhi Zhang and Lijuan Zhang for the help and support at the BL08U1 beamline, Jingyuan Ma at the BL14W1 beamline, Jichao Zhang at the BL15U1 beamline, and Jiajia Zhong, Xiaojie Zhou, and Yuzhao Tang at the BL01B1 of the Shanghai Synchrotron Radiation Facility (SSRF). This work was funded by the National Key Research and Development Program of China (2016YFD0200301) and the National Natural Science Foundation of China (41371248).
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