High boron stress leads to sugar beet (Beta vulgaris L.) toxicity by disrupting photosystem Ⅱ

Ecological characteristics of sugar beet plant and rhizosphere soil in response to high boron stress: A study of the remediation potential

High boron (B) stress degrades the soil environment and reduces plant productivity. Sugar beet has a high B demand and potential for remediation of B-toxic soils. However, the mechanism regarding the response of sugar beet plants and rhizosphere soil microbiome to high B stress is not clear. In the potted soil experiment, we set different soil effective B environments (0.5, 5, 10, 30, 50, and 100 mg kg-1) to study the growth status of sugar beets under different B concentrations, as well as the characteristics of soil enzyme activity and microbial community changes. The results showed that sugar beet growth was optimal at 5 mg kg-1 of B. Exceeding this concentration the tolerance index decreased. The injury threshold EC20 was reached at an available B concentration of 35.8 mg kg-1. Under the treatment of 100 mg kg-1, the B accumulation of sugar beet reached 0.22 mg plant-1, and the tolerance index was still higher than 60%, which had not yet reached the lethal concentration of sugar beet. The abundance of Acidobacteriota, Chloroflexi and Patescibacteria increased, which was beneficial to the resistance of sugar beet to high B stress. In summary, under high B stress sugar beet had strong tolerance, enhanced capacity for B uptake and enrichment, and changes in soil microbial community structure. This study provides a theoretical basis for clarifying the mechanism of sugar beet resistance to high B stress and soil remediation.

Research on phytotoxicity assessment and photosynthetic characteristics of nicosulfuron residues on Beta vulgaris L

Nicosulfuron is a common herbicide used to control weeds in maize fields. In northeast China, sugar beet is often grown as a subsequent crop after maize, and its frequently suffers from soil nicosulfuron residue damage, but the related toxicity evaluation and photosynthetic physiological mechanisms are not clear. Therefore, we experimented to evaluate the impacts of nicosulfuron residues on beet growth, photochemical properties, and antioxidant defense system. The results showed that when the nicosulfuron residue content reached 0.3 μg kg-1, it inhibited the growth of sugar beet. When it reached 36 μg kg-1 (GR50), the growth stagnated. Compared to the control group, a nicosulfuron residue of 36 μg kg-1 significantly decreased beet plant height (70.93 %), leaf area (91.85 %), dry weights of shoot (70.34 %) and root (32.70 %). It also notably reduced the potential photochemical activity (Fv/Fo) by 12.41 %, the light energy absorption performance index (PIabs) by 46.09 %, and light energy absorption (ABS/CSm) by 6.56 %. It decreased the capture (TRo/CSm) by 9.30 % and transferred energy (ETo/CSm) by 16.13 % per unit leaf cross-section while increasing the energy flux of heat dissipation (DIo/CSm) by 22.85 %. This ultimately impaired the photochemical capabilities of PSI and PSII, leading to a reduction in photosynthetic performance. Furthermore, nicosulfuron increased malondialdehyde (MDA) content while decreasing superoxide dismutase (SOD) and catalase (CAT) activities. In conclusion, this research clarified the toxicity risk level, lethal dose, and harm mechanism of the herbicide nicosulfuron residue. It provides a theoretical foundation for the rational use of herbicides in agricultural production and sugar beet planting management.