Growth status and physiological changes of sugar beet seedlings in response to acidic pH environments

Sugar beet (Beta vulgaris L.) is an important sugar crop that is popularly cultivated in a variety of agriculture conditions. Here, we studied sugar beet growth in different pH soils (pH 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, and 9.0) and analyzed their growth status and physiology. Sugar beet growth was best at pH 9.0 and worst at pH 5.0. As the soil pH decreased from 9.0 to 5.0, the osmoregulatory substances, antioxidant enzyme activity, and elemental contents in leaves and roots showed increasing trends, while photosynthesis and macronutrient contents showed decreasing trends. To explore the physiological mechanisms sugar beet use to respond to different pH environments, we analyzed the correlations between leaf net photosynthesis rate and physiological changes and nutrient contents of sugar beet. One of the factors inhibiting sugar beet growth in low pH soils was a reduction in photosynthetic capacity. The accumulation of osmoregulatory substances and increased peroxidative damage may have led to the decrease in leaf net photosynthesis rate. Furthermore, the decrease in nutrient content and accumulation of metal elements were correlated with the decrease in leaf photosynthetic rate. QRT-PCR analysis showed higher expression levels of antioxidant enzyme genes in the leaves and roots of sugar beet grown in low pH environments compared to those in high pH environments. Correspondingly, antioxidant enzyme activity was significantly higher in beets in low pH environments than in beets in high pH environments. These results provide important insight into the physiological responses by which sugar beet can adapt to different pH soils.