December 22, 2022

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Micronutrients May Be Important Regulators of Soil Carbon Storage

New analysis of biogeochemical dataset reveals continental-scale linkages between soil carbon storage and the micronutrient manganese.

Nonlinear regression of relationship between total manganese (Mn) concentrations (mg kg-1) and total (a) carbon (C) and (c) nitrogen (N) stocks (kg m-2) in organic horizons across 16 sites. Violin plots show distribution of (b) C and (d) N data points associated with stocks.

[Reprinted with permission from Santos, F., and E. Herndon. "Plant-Soil Relationships Influence Observed Trends Between Manganese and Carbon Across Biomes." Global Biogeochemical Cycles 37 (2), e2022GB007412. DOI:10.1029/2022GB007412. © 2023 American Geophysical Union.]

The Science

Soil capacity to store carbon depends on interactions between plant inputs, soil minerals, and microbial communities. The role of micronutrients, such as manganese, in regulating carbon storage in soils or release to the atmosphere is not well understood. Soil fungi can use manganese to break down lignin, a difficult-to-degrade component of plant tissue, and manganese can also form minerals that bind and react with carbon. This study shows that soil carbon stocks decrease with increasing manganese content in surface organic soils across the United States. Additionally, enhanced plant uptake of manganese under moderately acidic soil pH enriches manganese in surface soils and may promote decomposition that decreases carbon stocks.

The Impact

Soils contain substantial amounts of carbon that can be stored for hundreds to thousands of years or released as greenhouse gases into the atmosphere. Interactions between plants and soils may influence soil carbon stocks by concentrating manganese (Mn), a micronutrient needed to break down leaf litter at the soil surface, but these relationships are poorly understood. Previous studies were limited to a few biomes, but suggested that high Mn concentrations in leaf litter reduce soil carbon storage in forest ecosystems. This work shows that soil carbon and nitrogen stocks decrease with increasing Mn consistently in soils from a database across the U.S., and that carbon and nitrogen stocks were more strongly correlated with Mn than with climatic variables (i.e., temperature and precipitation). The demonstration of these continental scale linkages will help further our understanding of the mechanisms of soil carbon accumulation.

Summary

Manganese is an essential plant nutrient that plays a critical role in litter decomposition by oxidizing and degrading complex organic molecules. Using a continental-scale database from the National Ecological Observatory Network (NEON), researchers found that carbon storage in organic soil horizons decreases with increasing manganese content. This finding implies that manganese may promote breakdown of plant matter into carbon dioxide gas that is released into the atmosphere or into smaller compounds leached into underlying mineral soil. Results also show that plant uptake of dissolved manganese from soil and its release back to the soil through litterfall enriches manganese in surface soils under moderately acidic soil pH. Researchers also found that foliar manganese was strongly correlated with foliar lignin, indicating complex links between leaf chemistry and decomposability.

Principal Investigator

Elizabeth Herndon
Oak Ridge National Laboratory
[email protected]

Funding

This work was sponsored by the Laboratory-Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U.S. Department of Energy (DOE) under contract DE-AC05-00OR22725, project number 9958. Support was also received from the Critical Interfaces Science Focus Area sponsored by the Biological and Environmental Research (BER) Program within DOE’s Office of Science. This material is based in part upon work supported by the National Science Foundation through the National Ecological Observatory Network (NEON).

References

Santos, F., and E. Herndon. "Plant-Soil Relationships Influence Observed Trends Between Manganese and Carbon Across Biomes." Global Biogeochemical Cycles 37 (2), e2022GB007412  (2023). https://doi.org/10.1029/2022GB007412.