Effects of Seedling-Water Irrigation Levels on Rhizosphere Environment and Root Differentiation in Sweet Potato (Ipomoea batatas) in the Rooting and Branching Period

Abstract

Seedling-water can effectively ensure the survival of sweet potato seedlings after transplanting. However, improper irrigation of acclimation water can lead to an uncoordinated rhizosphere environment, negatively affecting the formation of storage roots. We conducted field experiments to assess the effects of three seedling-water irrigation treatments on sweet potato root differentiation, monitoring soil water content (SWC), O₂ and CO₂ concentrations, and temperature at 0–30 cm depths, while measuring the expression of genes related to sweet potato root differentiation, shoot biomass, the number of storage roots per plant (NSRPP), and yield. The results indicated that the moderate irrigation treatment (W2) significantly increased NSRPP and yield compared to the insufficient irrigation treatment (W1) and excessive irrigation (W3). Specifically, NSRPP for W2 increased by 48.9% (2022) and 73.2% (2023) relative to W1, and by 12.7% (2022) and 14.1% (2023) compared to W3. Similarly, yield improved by 43.1% (2022) and 32.3% (2023) compared to W1, and by 11.0% (2022) and 23.8% (2023) compared to W3. Correlation analysis revealed that NSRPP is positively correlated with the expression levels of cambium-related genes (IbSRD1 and IbNAC083), while it is negatively correlated with the expression levels of xylem-related genes (IbCAD1, IbEXP1 and IbPAL1). PLS-SEM analysis indicated that soil SWC and soil CO₂ concentrations significantly influenced NSRPP, whereas temperature and soil O₂ concentrations had no significant effect. Multivariate analyses of SWC, soil CO₂ concentrations, and NSRPP revealed that the optimal amount of irrigation ranges from 112.2 to 209.5 m³ hm⁻². These conditions ensured that water, gas, and heat conditions in the rhizosphere are maintained within a range conducive to root differentiation, ensuring that a greater proportion of root differentiation events develop into storage roots. The findings of this study will provide practical guidance for water management during the rooting and branching periods of sweet potatoes.