Early transplantation reshapes desert soil microbiomes and inferred interactions, with irrigation as a stabilizing input

Frequent drought and variable rainfall limit tree establishment in drylands. Over a 4-month field trial, we examined how early acacia seedling transplantation and irrigation pulses shape desert soil microbiomes, and whether irrigation primarily stabilizes transplant-associated trajectories rather than driving them. Moisture formed the dominant environmental gradient across treatments, while early transplantation shifted bulk-soil stoichiometric ratios, with water and vegetation lowering C/N and altering nutrient context. Using 16S rRNA gene and ITS2 region amplicon sequencing together with time-series generalized Lotka-Volterra modeling, we assessed changes in community composition and inferred interaction signs at phylum and genus resolution. Seedling transplantation exerted a stronger influence on microbial diversity and genus-level composition, whereas irrigation mainly modified the magnitude and stability of inferred interaction patterns. Phylum-level responses were comparatively stable, but genus-level trajectories diverged across vegetation × irrigation combinations. Model-based growth tendencies and inferred interaction signs were consistent with resilience in non-watered bare soil, opportunistic responses under irrigation in bare soil, and a shift toward more negative inferred associations in vegetated non-watered soil, whereas irrigated vegetated soil showed higher connectivity and a higher proportion of positive inferred links. Together, these results frame early transplantation as a discrete window of microbiome assembly in desert soils and support a testable hypothesis for nursery-to-field workflows. Irrigation may primarily function as a stabilizing input to a seedling-associated microbiome state, while establishment outcomes and functional mechanisms require direct validation.