Root microorganisms enhance crop resistance to low-temperature stress by increasing antioxidant enzyme activity

At low temperatures, alterations in root-associated microorganisms enhance the antioxidant enzyme activity in plants, thereby increasing their stress resistance. Low-temperature stress is an important environmental factor that restricts plant growth and development. While microbial inoculants play a significant role in alleviating plant low-temperature stress, the specific mechanisms involved remain unclear. This study evaluated the effects of exogenously applied microbial inoculants (composed of Clostridium sensu stricto, Altererythrobacte, Gemmatimona, Stenotrophomona, and Leclerici) on tobacco seedling growth, antioxidant enzyme activity, and root surface microbial communities under low-temperature stress, as well as the interrelationships among these factors. Under low-temperature stress, plants were treated with increasing volumes of functional microbial agents at three levels (T1, T2, T3), compared to a control (CK) without inoculation. The results indicated that the application of microbial inoculants significantly promoted the growth of tobacco seedlings. Root growth and dry matter accumulation of tobacco seedlings were positively correlated with the amount of microbial inoculum applied. Furthermore, microbial inoculants significantly enhanced the activities of antioxidant enzymes (POD, CAT, and SOD) in tobacco seedlings. The T3 treatment increased these activities by 191.1%, 234.68%, and 268.37%, respectively. Network analysis and correlation analysis identified key bacterial genera associated with the cold resistance of tobacco seedlings, namely, Arthrobacter, Asticcacaulis, Rhodobacter, and Chitinophaga, which showed a significant positive correlation with the growth of tobacco seedlings. The increase in these microbial populations significantly enhanced the dry matter accumulation and the relative abundance of antioxidant capacity in tobacco seedlings, indicating that the changes in the structure and function of these plant-associated communities are one of the important reasons for the improved stress resistance of flue-cured tobacco seedlings under low-temperature stress. Partial least squares path modeling (PLS-PM) analysis revealed that the key microbial genera significantly influenced the growth of tobacco seedlings by affecting the activity of antioxidant enzymes. The results above indicate that exogenous microbial agents alleviate low-temperature stress by altering the composition of microbial communities and affecting the activity of plant antioxidant enzymes. This study provides new research perspectives for sustainable agricultural development and mitigating crop low-temperature stress.