Polysaccharides from Ulva prolifera promote tobacco plant growth by benefiting rhizosphere bacterial community in acidic soil

Abstract

The application of biostimulants is an effective strategy to enhancing plant growth and bolstering stress resilience. However, our understanding of the effects of polysaccharides from Ulva prolifera (PUP) on plant growth under abiotic stress remains limited. In this study, the effects of 100 mg/L (PUP-1), 300 mg/L (PUP-3), 500 mg/L (PUP-5) of PUP and water (CK) on the tobacco (Nicotiana tabacum L.) seedling growth in the acidic soil were compared by a microcosm experiment. The results indicated that PUP-1, PUP-3, and PUP-5 significantly increased the fresh weight by 24 %-70 %, respectively, potentially due to elevated levels of carotenoid, chlorophyll a, and chlorophyll b. PUP significantly improved properties and fertility of the acidic soil, such as pH, available potassium (S-AK), available phosphorus (S-AP), sucrase (S-SU), total nitrogen (S-TN), urease (S-UR), and acid phosphatase (S-APA). The abundances of some beneficial bacteria (Gemmatimonadaceae, Bacillus and Nitrospira) were enhanced by PUP-3 treatment, which might be associated with the increased pH and nutritional status of the soil. Moreover, the increase in the abundance of functional genes in biosynthesis pathways of carbon metabolism, amino acids, secondary metabolites, and fatty acids also demonstrated the positive effect of PUP amendments. Among them, PUP-3 (300 mg/L) treatment significantly promoted tobacco growth and optimized soil microbial composition, while higher concentrations (PUP-5) did not show further gains. In summary, the applications of PUP showed great potentials in the enhancement of plant growth in the acidic soil, and 300 mg/L is the optimal application concentration of this polysaccharide preparation in tobacco cultivation.