Soil respiration is a critical process that regulates key ecosystem functions such as climate control, nutrient cycling, and plant productivity. Soil texture, nutrient availability, and microbial communities can all influence soil respiration, yet our understanding of their relative importance remains limited. This study aimed to investigate how different factors—like soil texture, nutrient additions, and microbial communities—contribute to soil respiration and define their specific roles in its variability. Using a microcosm experiment with various fertilizers and two soil types (Navarra, a silty clay soil, and Saponi, a sandy soil), we measured changes in both biotic and abiotic factors. A multiple linear regression analysis revealed that, among other biotic and abiotic factors, soil clay content, soluble nitrogen levels, bacterial abundance, and α-diversity significantly impacted soil respiration, together accounting for over 60% of its total variance. Structural equation modeling indicated that microbial communities made the greatest contribution to respiration at 30.84%, followed by soil texture at 19.63%. Overall, biotic factors were found to play a more significant role in driving soil respiration rates compared to abiotic factors, with edaphic properties having a greater influence than fertilizer additions.

Soil aggregates, which are highly influenced by land conversion, play key roles in driving soil nutrient distribution and microbial colonization. However, the role of soil aggregates in shaping the responses of microbial community composition and multiple ecosystem functions, especially ecosystem multifunctionality (EMF), to land conversion remains poorly understood. In this study, we investigated the impact of the conversion of a longan orchard (LO) to a conventional tea plantation (CTP) and organic tea plantation (OTP) on soil EMF at the aggregate level and explored the underlying mechanism. Our results showed that EMF was significantly reduced in the conventional tea plantation, with 3.44, 1.79, and 1.24 times for large macro-, macro-, and micro-aggregates. In contrast, it was relatively preserved in the organic tea plantation. Notably, micro-aggregates with higher microbial biomass supported more EMF than larger aggregates under the land conversion conditions. The EMF associated with soil aggregates was found to be regulated by the differences in nutrient content and microbial community composition. Random forest analysis, redundancy analysis, and Pearson analysis indicated that both soil nutrient and microbial community composition within soil aggregates jointly determined EMF. This study highlights that soil aggregation influences the stratification of nutrients and microbial communities, which leads to the differing response of aggregate-related EMF to land conversion.