Interaction between POM and pore structure during straw decomposition in two soils with contrasting texture

Particulate organic matter (POM) decomposition is influenced by soil pore structure, and the volume loss associated with POM decomposition might also promote the generation of new pores. However, the interaction between POM decomposition and soil pore structure remains unclear. Therefore, the objective of this study was to explore this interaction during straw decomposition. A 57-day soil incubation experiment was conducted using ¹³C-labelled maize straw in both Shajiang black soil and Fluvo-aquic soil, with two bulk densities (1.2 g/cm³, T1.2 and 1.5 g/cm³, T1.5). The loss of POM volume and the changes in soil pore structure, both before and after the incubation experiment, were quantified using X-ray micro-computed tomography (μCT). The results showed that there was a significantly greater volume loss of POM in Shajiang black soil (POM volume loss: 58.2–75.0 %) compared to Fluvo-aquic soil (34.0 %). Within the Shajiang black soil, decomposition of POM and the release of respired ¹³CO₂ were notably higher in the soil from the T1.2 treatment compared to the T1.5 treatment (P<0.05), while no significant difference was observed in Fluvo-aquic soil. Image-based porosity and mean pore distance emerged as primary determinants of POM variations in Shajiang black soil. Furthermore, our results underscore the positive role of pores ranging from 50 to 300 μm in diameter (Ø) in facilitating rapid POM decomposition, as evidenced by a higher ¹³CO₂ release. In Shajiang black soil, POM decomposition increased the porosity of 100–200 μm, 200–300 μm, and >300 μm Ø pores by 26.2 %, 51.8 % and 82.9 %, respectively, in the T1.2 treatment (P<0.05), and 50–100 μm Ø pores by 24.7 % in the T1.5 treatment (P<0.05). Our findings emphasize the significance of 100–300 μm Ø pores in gas transport and fresh POM decomposition, highlighting the pivotal role of POM decomposition in shaping soil pore structure.