Contrasting microbial and environmental associations link water availability to soil multifunctionality in the rhizosheath and bulk soil of Eremopyrum distans

Introduction Changes in water availability can alter soil resources and microbial communities, but whether association structures linking water availability to soil multifunctionality (SMF) differ between the root–soil interface and bulk soil remains unclear. Methods We subjected Eremopyrum distans to five water treatments over one growing season and assessed dimension-weighted and threshold-based SMF, together with bacterial, fungal and protistan community attributes, in the rhizosheath and bulk soil. Results Dimension-weighted SMF generally increased across the imposed water-treatment gradient. At higher functional thresholds, W + 25 supported more functions at high levels, particularly in bulk soil. After accounting for water treatment, microhabitat and their interaction, C- and N-related functions were associated mainly with microbial diversity, whereas P-related functions and high-threshold SMF were more closely associated with network complexity and the community-stability proxy. Piecewise structural equation models indicated that, in the rhizosheath, soil moisture was associated with SMF primarily through modeled indirect associations involving integrated microbial diversity, network complexity and the community-stability proxy. In bulk soil, the positive direct association of soil moisture and the negative direct association of soil pH with SMF were more prominent. Formal paired-bootstrap comparisons showed that most corresponding paths did not differ between microhabitats, although selected path differences were detected across SMF thresholds. Conclusion Water availability was associated with SMF through microhabitat-dependent association structures. Microbial community organization was more closely associated with SMF in the rhizosheath, whereas local environmental conditions retained stronger direct associations with SMF in bulk soil. These findings highlight the importance of distinguishing rhizosheath and bulk-soil microhabitats when evaluating soil functional responses to changing water availability.