Soil clay content shapes the elevation distribution of soil organic carbon fractions via modulating microbial cross-kingdom interactions

Soil microbial interactions are crucial in maintaining ecosystem functions and the carbon (C) cycle. However, the regulatory mechanism of microbial cross-kingdom interactions on soil organic C (SOC) fractions remains unclear. Here, we collected soil samples along two independent elevation gradients in Zhongtiao Mountain (ZT) and Wutai Mountain (WT) in China. We used co-occurrence networks to investigate how cross-kingdom microbial interaction patterns are potentially linked to microbial metabolism and the distribution of particulate organic C (POC) and mineral-associated organic C (MAOC). We found that cross-kingdom interactions, particularly bacterial-fungal (competition) and protistan-bacterial (predation) networks, showed stronger associations with microbial metabolism than intra-kingdom interactions. Intensified cross-kingdom interactions were associated with reduced POC and MAOC by decreasing the microbial necromass accumulation coefficient (NAC) and increasing the microbial metabolic quotient (qCO 2 ) in both mountains. Further analysis showed that cross-kingdom interactions were linked to clay content, with a decrease in clay content providing more favorable habitats for fungi and protists, potentially intensifying competition and predation among microorganisms. The decrease in clay content along elevations in the ZT and its increase in the WT corresponded to contrasting elevation distributions in microbial cross-kingdom interactions, microbial metabolism (NAC and qCO 2 ), POC, and MAOC. Thus, these findings suggest a link between microbial community interactions and SOC, emphasizing that microbial cross-kingdom networks, which vary with soil texture and ecosystems, may play a key role in soil C dynamics through regulating microbial metabolism.