Heterogeneous root zone salinity mitigates salt hazards through the regulation of rhizosphere microorganisms and root metabolites in cucumber

Abstract

Salinity represents a major abiotic constraint limiting plant productivity in natural ecosystems. A key characte-ristic of saline soils is their inherent spatial heterogeneity in salt distribution, yet current understanding of plant responses to salinity primarily derives from homogeneous exposurescenarios, with limited data availableon root zone adaptation mechanisms under heterogeneous salinity conditions. To address this knowledge gap, we employed a split-root experimental system to systematically compare cucumber responses to heterogeneous versus homogeneous salinity at equivalent total salt concentrations. Our findings demonstrate that cucumber roots exhibited pronounced compensatory growth in low-salinity compartments, concomitant with enhanced osmotic adjustment capacity in high-salinity root zones. This differential adaptation resulted in significantly improved growth performance (P<0.05) and photosynthetic efficiency under heterogeneous salinity compared to homogeneous treatment. Moreover, rhizosphere microbiome analysis revealed enrichment of halotolerant rhizosphere microbiota (e.g., Rhizobiaceae, Xanthomonadaceae) under heterogeneous conditions. Metabolomic profiling identified significant accumulation of osmolytes (proline) and organic acids (e.g., citrate) in high-salinity root sectors, showing strong positive correlations with beneficial bacterial populations. In conclusion, through compensatory growth responses and modulation of rhizosphere microbial communities, the cucumber plants effectively alleviated the detrimental effects of heterogeneous salinity stress by optimizing water and resource allocation at the whole-plant level.

Graphical abstract

Keywords

heterogeneous salinity / rhizosphere microbiome / metabolites / compensatory growth / water distribution

Highlight

	● Heterogeneous root zone salinity mitigated salt injury to Cucumis sativus L.
	● The heterogeneous salt rhizosphere had more Proteobacteria and Bacteroidetes.
	● The roots on the high salt side possessded more organic acids and amino acids.
	● The rhizosphere bacteria displayed a positive correlation with metabolites.

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