Fungal assembly and root-fungal interactions mediate water-oxygen coupling effects on tomato growth in saline soil under nanobubble-oxygenated drip irrigation

Abstract

Nanobubble-oxygenated drip irrigation (NODI) mitigates the dual stress of high salinity and hypoxia on crop growth in salinized soils. However, while the responses of bacterial communities to NODI have been documented, the regulatory mechanisms on soil fungal community assembly and root–fungal interactions remain unclear. This knowledge gap hinders a comprehensive understanding of NODIʼs role in enhancing crop productivity. To address this, we employed a dual-factor experiment combining irrigation amount (deficit: I_0.8, full: I₁, excess: I_1.2) and dissolved oxygen concentration (DO: 5, 15, 30 mg L⁻¹). This study aimed to investigate the effects of NODI on fungal communities and root systems in mildly salinized tomato soil, thereby elucidating the mechanisms of water-oxygen coupling in regulating crop growth through root–fungal interactions. The results indicated: (1) High dissolved oxygen (DO₃₀) significantly reduced soil electrical conductivity (EC) (by 34.87% and 34.09% compared to DO₅ and DO₁₅, respectively; P ⩽ 0.05), enhanced modularity and keystone taxa abundance in fungal co-occurrence networks, and increased the relative abundance of saprotrophic functions (e.g., Dung Saprotroph–Undefined Saprotroph), endophytic functions (e.g., Endophyte), and the proportion of homogeneous selection indeterministic assembly; (2) Different DO-I combinations led to significant variations in therelative abundance of fungal phyla (Ascomycota, Basidiomycota, Olpidiomycota, Rozellomycota, Zoopagomycota) and five functional guilds (P ⩽ 0.05); (3) Root architecture (tips, forks, etc.) and EC jointly drove fungal community variation. Root tips exhibited a significant positive correlation with the relative abundance of arbuscular mycorrhizal fungi. The structural equation modeling (SEM) revealed that Forks indirectly affected yield by modulating Basidiomycota abundance (r=0.51), while saprotrophs (Dung Saprotroph–Undefined Saprotroph) directly promoted yield under low EC (<35 mS cm⁻¹) (r= 0.54); (4) The optimal treatment DO₃₀I_1.2 (30 mg L⁻¹ DO and 20% excess irrigation) minimized root-zone EC (32.40 mS cm⁻¹) and achieved peak tomato yield (210.90 kg plot⁻¹) and lycopene content (56.92 μg g⁻¹). In conclusion, NODI optimizes the rhizosphere microenvironment through water-oxygen coupling, activates saprotrophic functions, and strengthens root-fungal symbiotic networks, thereby enhancing tomato yield and quality in salinized soils. DO₃₀I_1.2 is recommended as the optimal application mode.

Graphical abstract

Keywords

water-oxygen coupling / nanobubble-oxygenated drip irrigation / saline soil / fungal communities / root-fungal interactions / tomato

Highlight

	● Nanobubble-oxygenated drip irrigation (NODI) mitigates the dual stress of high salinity and hypoxia on crop growth in salinized soils.
	● Water-oxygen coupling (DO-I combinations) significantly altered fungal community composition (key phyla) and functional guild abundances.
	● High DO (30 mg L−1) in NODI reduced soil salinity (EC) by about 34%, enhanced fungal network stability and modularity.
	● Optimal DO30I1·2 mode (30 mg L−1 DO and 20% excess irrigation) minimized EC and maximized tomato yield and lycopene content.

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