Soil water deficit is an important factor affecting the source–sink balance of sweet potato during its late-season growth, but water regulation during this period has not been well studied. Therefore, the aim of this study was to determine the appropriate irrigation level in late-season sweet potato, and the effect of irrigation level on accumulation and allocation of photosynthetic products. In this study, two yield-based field trials (2021–2022) were conducted in which five late-season irrigation levels set according to the crop evapotranspiration rate were tested (T₀: non-irrigation, T₁: 33% ET_c, T₂: 75% ET_c, T₃: 100% ET_c, T₄: 125% ET_c). The effects of the different irrigation levels on photosynthetic physiological indexes, ¹³C transfer allocation, water use efficiency (WUE), water productivity (WP), and the yield and economic benefit of sweet potato were studied. The results showed that late-season irrigation significantly increased the total chlorophyll content and net photosynthetic rate of functional leaves, in addition to promoting the accumulation of above-ground-source organic biomass (p < 0.05). The rate of ¹³C allocation, maximum accumulation rate (V_max), and average accumulation rate (V_mean) of dry matter in storage root were significantly higher under T₂ irrigation than under the other treatments (p < 0.05). This suggests that both non-irrigation (T₀) and over-irrigation (T₄) were not conducive to the transfer and allocation of photosynthetic products to storage roots in late-season sweet potato. However, moderate irrigation (T₂) effectively promoted the source–sink balance, enhanced the source photosynthetic rate and stimulated the sink activity, such that more photosynthate was allocated to the storage sink. The results also showed that T₂ irrigation treatments significantly increased yield, WUE and WP compared to T₀ and T₄ (p < 0.05), suggesting that moderate irrigation (T₂) can significantly promote the potential of storage root production and field productivity. There was a close relationship between economic benefit and marketable sweet potato yield, and both were highest under T₂ (p < 0.05), increasing by 36.1% and 59.9% compared with T₀ over the two-year study period. In conclusion, irrigation of late-season sweet potato with 75% evapotranspiration (T₂) can improve both the yield and production potential. Together, these results support the use of late-season water management in the production of sweet potato.

In the context of climate change and severe water shortages in agriculture, we explored water stress responses in the sweet potato (Ipomoea batatas) in terms of endogenous hormone levels and other physiological characteristics, providing a theoretical basis for drought-resistant cultivation of sweet potato. This study was conducted from 2021–2022 in a solar greenhouse under artificially controlled water conditions. We determined biomass, agronomic indexes, photosynthetic parameters, and endogenous hormone levels in three treatments: normal water supply (CK), mild drought (LD), and severe drought (HD). The results revealed that drought stress inhibited aboveground and belowground sweet potato growth compared with CK; sweet potato yield decreased with increasing drought. The net photosynthetic rate, stomatal conductance, and transpiration rate of sweet potato leaves decreased significantly under drought stress. The leaves’ intercellular CO₂ concentration (Ci) decreased with increasing drought up to 50 days after transplanting but increased with increasing drought up to 75 days after transplanting. The zeatin riboside (ZR) and indole-3-acetic acid (IAA) contents were significantly lower in sweet potato leaves and tubers in the LD and HD treatments compared with CK, whereas the abscisic acid (ABA) content was significantly higher. Within the same period, the (ZR + IAA)/ABA ratio decreased with increasing drought severity. Correlation analysis revealed that the ABA and leaf Ci were significantly positively correlated, and both indices were significantly negatively correlated with all other indices. Aboveground dry weight was significantly correlated with the ZR and IAA contents. These findings demonstrate the regulatory effects of elevated leaf ABA concentrations on stomatal conductance during drought and indicate that stomatal closure was mainly responsible for the decreased photosynthetic rate observed in the early stage of drought. The rapid decrease in the photosynthetic rate in the late stage of drought may have been caused by non-stomatal factors. These findings provide a theoretical foundation for future drought-resistant sweet potato cultivation.

Drought stress severely limits the productivity of sweet potato (Ipomoea batatas L.), yet the stage-specific molecular mechanisms of its adaptation remain poorly understood. Therefore, we integrated transcriptomics and extensive targeted metabolomics analysis to investigate the drought responses of the sweet potato cultivar ‘Luoyu 11’ during the branching and tuber formation stage (DS1) and the storage root expansion stage (DS2) under controlled drought conditions (45 ± 5% field capacity). Transcriptome analysis identified 8292 and 13,509 differentially expressed genes in DS1 and DS2, respectively, compared with the well-watered control (75 ± 5% field capacity). KEGG enrichment analysis revealed the activation of plant hormone signaling, carbon metabolism, and flavonoid biosynthesis pathways, and more pronounced transcriptional changes were observed during the DS2 stage. Metabolomic analysis identified 415 differentially accumulated metabolites across the two growth periods, with flavonoids being the most abundant (accounting for 30.3% in DS1 and 23.7% in DS2), followed by amino acids and organic acids, which highlighted their roles in osmotic regulation and oxidative stress alleviation. Integrated omics analysis revealed stage-specific regulation of flavonoid biosynthesis under drought stress. Genes such as CYP75B1 and IF7MAT were consistently downregulated, whereas flavonol synthase and glycosyltransferases exhibited differential expression patterns, which correlated with the selective accumulation of trifolin and luteoloside. Our findings provide novel insights into the molecular basis of drought tolerance in sweet potato and offer actionable targets for breeding and precision water management in drought-prone regions.

Sufficient soil moisture is required to ensure the successful transplantation of sweet potato seedlings. Thus, reasonable water management is essential for achieving high quality and yield in sweet potato production. We conducted field experiments in northern China, planted on 18 May and harvested on 18 October 2021, at the Nancun Experimental Base of Qingdao Agricultural University. Three water management treatments were tested for sweet potato seedlings after transplanting: hole irrigation (W₁), optimized drip irrigation (W₂), and traditional drip irrigation (W₃). The variation characteristics of soil volumetric water content, soil temperature, and soil CO₂ concentration in the root zone were monitored in situ for 0–50 days. The agronomy, root morphology, photosynthetic parameters, ¹³C accumulation, yield, and yield components of sweet potato were determined. The results showed that soil VWC was maintained at 22–25% and 27–32% in the hole irrigation and combined drip irrigation treatments, respectively, from 0 to 30 days after transplanting. However, there was no significant difference between the traditional (W₃) and optimized (W₂) drip irrigation systems. From 30 to 50 days after transplanting, the VWC decreased significantly in all treatments, with significant differences among all treatments. Soil CO₂ concentrations were positively correlated with VWC from 0 to 30 days after transplanting but gradually increased from 30 to 50 days, with significant differences among treatments. Soil temperature varied with fluctuations in air temperature, with no significant differences among treatments. Sweet potato survival rates were significantly lower in the hole irrigation treatments than in the drip irrigation treatments, with no significant difference between W₂ and W₃. The aboveground biomass, photosynthetic parameters, and leaf area index were significantly higher under drip irrigation than under hole irrigation, and values were higher in W₃ than in W₂. However, the total root length, root volume, and ¹³C partitioning rate were higher in W₂ than in W₃. These findings suggest that excessive drip irrigation can lead to an imbalance in sweet potato reservoir sources. Compared with W₁, the W₂ and W₃ treatments exhibited significant yield increases of 42.98% and 36.49%, respectively. The W₂ treatment had the lowest sweet potato deformity rate.

An open question with regard to the community ecology of arbuscular mycorrhizal fungi (AMF) concerns how to best amplify AMF in the soil, which contains a large proportion of DNA from AM extra-radical mycelium and spores. However, to date, a direct comparison of AMF primers for soil samples, which would systematically assess their amplification efficiency, is still missing. In our present study, we compared and characterized four widely used primer sets targeting AMF 18S rDNA or SSU-ITS-LSU rDNA from three soil samples as follows: (1) SSUmAf/LSUmAr + SSUmCf/LSUmBr, (2) GeoA2/Geo11 + NS31/AM1, (3) AML1/AML2 + NS31/AM1 and (4) AMV4.5NF/AMDGR. These primer sets were compared in terms of the proportion of Glomeromycota detected, AMF diversity and community composition. Our data revealed that the newly combined primer set 3 was the most suitable one for amplifying AMF from soil samples. It yielded the highest AMF alpha diversity, and was very specific to Glomeromycota. Primer set 2 was unable to amplify Claroideoglomus from soil 1, which was the dominant AMF clade as proved by other three primer sets. Primer set 4 demonstrated its instability among different soil samples, since the proportion of AMF in total sequences varied from 5% to 83%. Although primer set 1 showed the highest proportion of AMF (95–100%) in the soil samples, it captured the lowest AMF diversity, and the operational taxonomic units obtained by this primer set were only 36.4% of that by primer set 4. Taken together, our data suggested that AMF diversity in soil samples could be underestimated by primer set 1, 2 and 4. Our result confirmed the important role of the choice of AMF primers for analyzing AMF communities in soil and explored the most suitable one for amplifying AMF from soil samples.