Nutrient-Rich Mineral-Associated Organic Matter Limits Carbon Storage Under Elevated Carbon Dioxide in a Low Phosphorus Eucalyptus Woodland Soil

5 views

Skip to first unread message

Geoengineering News

unread,

Nov 5, 2025, 5:14:51 AM (4 days ago) Nov 5

to CarbonDiox...@googlegroups.com

https://pubmed.ncbi.nlm.nih.gov/41158003/

Authors

Anna Favaro, Yolima Carrillo, Balwant Singh, Charles Warren, Feike A Dijkstra

2025

Abstract

A rise in atmospheric CO2 concentration can have positive or negative effects on soil organic carbon (SOC) pools, with likely impacts on soil nutrient availability, which can in turn, drive ecosystem-level impacts. Much of the soil nutrients are locked in the more stable mineral-associated organic matter (MAOM) pool compared to the more labile particulate organic matter (POM) pool, but how elevated CO2 (eCO2) affects these pools is unclear. In this study, we examined how 12 years of eCO2 affected the POM and MAOM C, nitrogen (N), and phosphorus (P) pools at two different depths (0-10 and 10-20 cm) in a low P, native Eucalyptus woodland. Across soil depths, we found that 12 years of eCO2 caused significant decreases in MAOM-total C (16%), MAOM-organic N (15%), and MAOM-organic P (16%) compared to ambient CO2 (aCO2), but no effects on C, organic N (Norg), and organic P (Porg) in POM. The MAOM had consistently lower C: Porg and C: Norg ratios (228 and 12.4, respectively) than POM (655 and 24.1, respectively). Our results cannot be explained by eCO2-induced changes in plant inputs but instead suggest that the increased belowground C inputs under eCO2, in combination with low soil P availability, triggered a rhizosphere priming effect on the MAOM pool. Since MAOM was richer in P than POM, microbes may have preferentially mined MAOM for P (and N) to meet their P demand, thereby enhancing the decomposition of MAOM more than POM. While uncertainties remain about the fate of P after microbial death in this ecosystem, this study highlights that the nutrient-rich MAOM pool is vulnerable to rhizosphere priming, thereby restricting the potential for greater SOC accumulation under eCO2 in soils with low P availability.