Photosynthesis product allocation and yield in sweetpotato with different irrigation levels at mid-season

Abstract

Soil water deficit is one of the important factors affecting the source–sink balance of sweetpotato at mid-season growth (storage root initiation period). However, water regulation at mid-season sweetpotato growth is often ignored. In this study, field trials were conducted to diagnose leaves in the middle of sweetpotato growth, and then three mid-season irrigation levels (CK: 0 m3/hm2; W1: 150 m3/hm2; W2: 300 m3/hm2) were established. The effects of different irrigation levels on photosynthetic physiological indexes, 13C transfer allocation, and yield of sweetpotato were studied. The results revealed that mid-season irrigation significantly increased the relative moisture content of sweetpotato leaves, maximum photochemical efficiency (Fv/Fm), and net photosynthetic rate (Pn) (P < 0.05), which effectively alleviated the effects of soil water deficit. The Pn values with irrigation treatments W1 and W2 were significantly higher than those with control (CK) treatment in all three study periods. Among these, the W2 treatment had the highest Pn at 70 d, an increase of 113.4% compared with CK in 2019 test, and W1 had the highest Pn at 110 d and 150 d (P < 0.05). The trend of stomatal conductance (Gs) was basically consistent with Pn. The transpiration rate (Tr) of W2 was the highest at 70 d, an increase of 59.8–69.7% compared with CK, but the Tr of W1 was the highest at 110 d and 150 d. The 13C total accumulation in the W1 treatment was the highest at 70 d, 110 d, and 150 d, when it was 21.9%, 20.4%, and 33.1% higher than that of the W2 treatment in 2019 test (P < 0.05), respectively. The 13C allocation rate of storage roots treated with W1 was the highest in all periods, reaching as high as 73.1–76.1% at 150 d (P < 0.05). At 70 d, the 13C allocation rate of fiber roots and stems was highest in the CK treatment, whereas the 13C allocation rate of leaves was highest in W2 (P < 0.05). At 110 d and 150 d, the 13C allocation rate of stems and leaves in CK was the highest (P < 0.05). The biomass of W2 was the highest at 70 d, but the root-to-shoot ratio and the dry weight of root became gradually lower than those of the CK and W1 treatments at the late season, when they were reduced by 28.4% and 32.2% compared to W1 at 150 d in 2019 test (P < 0.05). The yield of W1 was increased significantly by 33.3–34.9% compared with CK (P < 0.05), but W2 only had an increased production of 14.5–20.7% (P < 0.05) compared to CK (P < 0.05). The irrigation water utilization efficiency of W2 was 59.4–61.8% and 39.1–43.5% lower than those of the CK and W1 treatments (P < 0.05), respectively. Together, these results validate the field sweetpotato mid-season water management model, which is of great significance for guiding actual production of sweetpotato and increasing the potential of sweetpotato.