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DOE OSTI · 3399444

Interaction of Soil pH and Mineralogy Controls Soil Organic Matter Persistence through Changes in the Composition and Amount of Microbial Necromass

Liu, Yuan [Michigan State University, East Lansing, MI (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)] (ORCID:0000000183505773)·Matus-Acuña, Violeta [Michigan State University, East Lansing, MI (United States)]·Tiemann, Lisa K. [Michigan State University, East Lansing, MI (United States)] (ORCID:0000000305146503)
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Abstract

Microbial necromass–mineral associations are key to long-term soil organic matter (SOM) persistence. However, how soil pH and mineralogy interact to regulate SOM stability remains poorly understood. Here, we used artificial soils to test how three clay minerals (bentonite, kaolinite, and goethite), adjusted to four pH levels (5–8), affect microbial activity (respiration), microbial physiology (carbon use efficiency, CUE), microbial-derived residue material (necromass), and the formation and stability of mineral-associated organic matter (MAOM). Artificial soils were inoculated with a rhizosphere-derived microbial community cultured under the same pH conditions and on two representative simulated exudate types (organic acids and carbohydrates) and incubated for 6 weeks. In two complementary experiments, we added necromass from known microbial taxa to the same minerals across pH levels to isolate the role of necromass chemistry and loading. We found that soil pH shaped MAOM chemistry by altering microbial activity and necromass composition. In interaction with mineral type, pH also controlled MAOM thermal stability. Higher necromass loading weakened mineral-organic bonding, reducing MAOM stability, consistent with zonal mineral–organic interaction models. Our results demonstrate that microbial activity, rather than carbon use efficiency, better predicts MAOM formation and that pH-dependent necromass composition and loading govern MAOM persistence. These findings advance mechanistic understanding of SOM stabilization and have implications for predicting soil carbon dynamics under shifting environmental conditions.

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carbon use efficiencyfunctional groupmineral-associated organic matternecromasspH gradientthermal stability

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Liu, Yuan [Michigan State University, East Lansing, MI (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)] (ORCID:0000000183505773), Matus-Acuña, Violeta [Michigan State University, East Lansing, MI (United States)], Tiemann, Lisa K. [Michigan State University, East Lansing, MI (United States)] (ORCID:0000000305146503). 2026-07-29. Interaction of Soil pH and Mineralogy Controls Soil Organic Matter Persistence through Changes in the Composition and Amount of Microbial Necromass. https://doi.org/10.1021/acs.est.6c08883

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