Differences in straw derived hydrophilic and hydrophobic carbon incorporation into soil microbial necromass

Abstract

Microorganisms are important modulators for transformation and allocation of straw-derived carbon into soil organic carbon (SOC). However, little is known about how straw-derived dissolved organic matter (DOM) is converted into microbial necromass carbon in soil. To address this, hydrophilic (Hi-DOM) and hydrophobic (Ho-DOM) carbon fractions were extracted from cotton straw and added to soil with a 10-year history of straw incorporation for a 45-day mineralization incubation. CO₂ emissions and ¹³C enrichment after addition of ¹³C-labeled Hi-and Ho-DOM into soil were analyzed, and the differences between the utilization of Hi-and Ho-DOM by microorganisms, as well as their incorporation into amino sugars were also determined. The results revealed that during the initial incubation phase (0.25–5 days), the mineralization rate of Hi-DOM was 1.1–2.7 times faster than that of Ho-DOM. Furthermore, cumulative CO₂ production gradually increased during the incubation, and by the end of the experiment, Hi-DOM yielded 1.4 times more CO₂ than Ho-DOM. Moreover, both Hi-DOM and Ho-DOM exhibited a positive priming effect. Similarly, the ¹³C content derived from Hi-DOM (0.48 mg g⁻¹) was noticeably higher than that from Ho-DOM (0.41 mg g⁻¹) in SOC. Residual ¹³C from Hi-DOM and Ho-DOM accounted for 20.1 % and 35.6 % of the total added carbon, respectively, indicating the dependence of microbial C uptake on substrate quality. Higher ¹³C-GlcN and ¹³C-MurN levels were witnessed in Ho-DOM and Hi-DOM-treated soils, respectively. Furthermore, Hi-DOM-treated soil exhibited higher bacterial necromass ¹³C and total microbial necromass ¹³C than Ho-DOM-treated soil, suggesting a fungal preference for complex compounds while bacteria preferred the utilization of simpler substrates for amino sugar formation. Furthermore, Hi-DOM exhibited prolonged and faster soil activity, as evidenced by significantly increased Hi-DOM-sourced ¹³C enrichment percentages in the amino sugar pool by the end of incubation. In conclusion, the distinct properties of straw-derived DOM can alter the intensity and magnitude of its conversion into microbial necromass carbon. Combined with the differential contributions of newly formed microbial residues to the SOC pool, this study enhances predictions of how straw carbon incorporation influences microbial carbon storage capacity and SOC sequestration potential.