A recent study, led by researchers from the Max Planck Institute for Biogeochemistry and the Martin Luther University Halle-Wittenberg, sheds light on the intricate factors influencing mineral-associated organic matter (MAOM) formation in soils. Published in Global Change Biology, the research underscores the critical role MAOM plays in carbon sequestration and its potential contribution to mitigating climate change.
Soil organic carbon, pivotal for soil fertility and food production, also plays a significant role in the Earth’s climate. Approximately 7% of atmospheric CO2 cycles through soils annually. However, since the advent of agriculture, soils have experienced substantial carbon losses to the atmosphere, necessitating a comprehensive understanding of how to prevent further losses and restore soil carbon stocks to address climate change.
The study focused on the interplay between mineral composition, land use, and management intensity in the formation of MAOM, a key process in the global carbon cycle. The researchers utilized over 3,500 permeable containers filled with carbon-free goethite and illite, representative iron oxide and silicate clay minerals, respectively. These containers were buried at 150 forest and 150 grassland sites across three German study regions.
After five years of incubation, the team, led by De Shorn Bramble and Susanne Ulrich, analyzed the container contents. The results revealed that irrespective of land use and management intensity, goethite accumulated four times more organic carbon than illite, emphasizing the decisive role of mineral composition in MAOM formation.
Susanne Ulrich, a Ph.D. candidate at MLU, highlighted the significance of the experimental setup, allowing for a direct comparison of carbon storage potential under field conditions. She noted that surface properties, rather than mineral surface area, determined MAOM formation, with oxides exhibiting a significantly larger potential for carbon storage than silicate clay minerals.
Contrary to previous beliefs about the resilience of MAOM formation to land use and management changes in short time scales, the researchers observed notable effects. In forests, MAOM formation was reduced by harvest intensity and influenced by tree species selection. In grasslands, plant productivity and diversity were found to increase MAOM formation, with fertilization affecting both parameters.
De Shorn Bramble, also a Ph.D. candidate at MPI-BGC, emphasized the groundbreaking nature of their results, revealing significant land use and management effects on MAOM formation in just five years. He emphasized that while mineral composition determines the potential for soil carbon storage, land use influences the realization of this potential. Bramble concluded that ongoing research is crucial to understanding the intricate interactions among plant productivity, organic input quality, and decomposer communities in MAOM formation under different management practices. This knowledge is essential for predicting how MAOM responds to human activities, contributing to informed and sustainable soil management strategies.