Preprints
https://doi.org/10.5194/egusphere-2025-310
https://doi.org/10.5194/egusphere-2025-310
04 Feb 2025
 | 04 Feb 2025
Status: this preprint is open for discussion and under review for SOIL (SOIL).

Microbial carbon use for incorporating biomass phosphorus drives CO2 emission in phosphorus-supplied subtropical forest soils

Jianghao Tan, Muhammed Mustapha Ibrahim, Huiying Lin, Zhaofeng Chang, Conghui Guo, Zhimin Li, Xianzhen Luo, Yongbiao Lin, and Enqing Hou

Abstract. Subtropical forests store significant amounts of soil organic carbon (SOC) and are important in the global C cycle. Current understandings based on controlled experiments indicate that phosphorus (P) availability promotes SOC decomposition by alleviating microbial P limitation or rendering SOC available for microbial decomposition. While no alternative mechanism is currently known, it is uncertain if this mechanism holds across soils or P supply levels at the field scale. We formulated an alternative mechanism for acidic subtropical forest soils where organic C (OC) is bound to iron (Fe). Our hypothesis proposed that P supply would promote Fe-bound P formation and desorption of OC previously bound to Fe, and the microbial utilization of the desorbed OC for P-cycling contributes significantly to CO2 emission. We tested our hypotheses by utilizing a forest P addition platform to explore C-dynamics, its regulators, and utilization across four P supply levels: 0, 25, 50, and 100 kg P ha-1 yr-1 (Con, P1, P2, and P3, respectively) for one year. Phosphorus supply significantly increased the periodic and cumulative dissolved OC (DOC) concentration, especially in P3, and was associated with increased iron (Fe)-bound P formation. With increased DOC following P addition, microbial biomass P (MBP) significantly increased, while MBC remained unchanged. The significantly positive relationship between MBP:MBC ratio and DOC, significant increase in MBP and carbon dioxide (CO2) emission with P addition, and the reduction in CO2 emission with increasing MBC:MBP ratio (0–10 cm) supports our results that the desorbed-C alleviated microbial C-limitation induced during P-cycling, particularly, MBP incorporation, to drive CO2 emission. Structural equation modeling and multivariate analyses projected MBP as a critical factor inducing CO2 emission. Besides, insignificant alterations in the relative abundance of C-degrading functional genes and reductions in P- and C-degrading enzyme activity indicated the sufficiency of desorbed OC for microbial use without further SOC degradation. Our study provides an alternative mechanism of P's impact on soil C-cycling processes in acidic subtropical forest soils vital for constraining process-based C models.

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Jianghao Tan, Muhammed Mustapha Ibrahim, Huiying Lin, Zhaofeng Chang, Conghui Guo, Zhimin Li, Xianzhen Luo, Yongbiao Lin, and Enqing Hou

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Jianghao Tan, Muhammed Mustapha Ibrahim, Huiying Lin, Zhaofeng Chang, Conghui Guo, Zhimin Li, Xianzhen Luo, Yongbiao Lin, and Enqing Hou
Jianghao Tan, Muhammed Mustapha Ibrahim, Huiying Lin, Zhaofeng Chang, Conghui Guo, Zhimin Li, Xianzhen Luo, Yongbiao Lin, and Enqing Hou

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Short summary
Controlled experiments show that adding phosphorus (P) to soils relieves microbial P limitation to degrade soil organic carbon (SOC). No alternative explanation currently exists. We show increased desorption of OC with P supply in subtropical forests, which was used to satisfy microbial C-limitation induced while incorporating P into microbial biomass, and driving CO2 emission, without further SOC degradation. We provide newer an alternative mechanism vital for constraining land C models.
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