Straw return enhances soil multifunctionality by promoting protist-dominated microbial multitrophic interactions

Straw return is a key cropland anthropogenic management that influences soil carbon sequestration, individual microbial biodiversity, and microbial functional profiles. Despite its importance, how microbe interactions across multiple trophic levels influence soil multifunctionality in response to straw return remains poorly understood, particularly in dryland agricultural ecosystems. Here, we investigated the influences of straw return on microbial hierarchical groups (bacteria, fungi, and protists) and the cascading effects on soil multifunctionality across different maize growth stages in an arid region. Our results showed that straw inputs increased Shannon diversity of bacteria and fungi communities during the filling and maturity stages, and that of the protist community at the maturity stage. Importantly, compared to non-straw treatment, straw return significantly increased soil multifunctionality by 16–22 % at filling and maturity stages. Moreover, we found that straw inputs shifted the soil multiple functions and multitrophic interaction networks from bacteria and fungi dominated to protist dominated. Straw return enhanced network connectivity by 50 %, as evidenced by a 50 % increase in linkages and a 43 % increase in node average edges. Furthermore, protist-dominated cross-trophic interactions primarily explained 51 % of variation in soil multifunctionality under straw return. Additionally, phagotrophic protists suppressed the relative abundance of Fusarium, while straw return enhanced the associations between phagotrophic protists and potential beneficial bacterial genera. These findings collectively indicate that crop straw return enhances soil multifunctionality by promoting higher trophic level microbial diversity and facilitating potential top-down regulations. Our study underscores the critical roles of protists in maintaining soil functions and provides novel insights into the ecological consequences of straw return on microbial hierarchical interactions and multiple microbially mediated ecosystem functions.