Soil amendment with sorbitol and mannitol changes the soil microbial community and its enzymatic activities

Sorbitol and mannitol have profound effects on plant growth, involving plant photosynthesis, respiration and developmental processes, and are also associated with plant health as rhizosphere exudates. However, studies on soil microbial activity and the quality of sugar alcohols as carbon source additives, especially amendments with sorbitol and mannitol, are rarely studied. Soil nutrients, enzyme activities and microbial communities were measured at 0.25, 0.5 and 1.0 mg sorbitol or mannitol per gram (fresh weight) soil (i.e. mass ratio of sugar alcohol to fresh soil). Increasing soil concentrations of the sugar alcohols led to significantly increased soil concentrations of available potassium and NO3−-N, reduced soil pH and enhanced soil enzyme activities. Soil nutrient levels were enhanced by the sugar alcohols, despite decreasing NO3−-N and available P contents, relative to the control, with mannitol having a greater effect than sorbitol at the same concentration. These two sugar alcohols altered the composition of the soil microbial communities, significantly increasing the soil bacterial communities involved in nitrogen fixation and ureolysis, as well as the proportions of Pseudomonadaceae and Verrucomicrobiaceae which were significantly positively correlated with a variety of enzymes in the soil, particularly invertases. In addition, Xanthomonadaceae, Sphingomonadaceae and Blastocatellaceae were significantly positively correlated with the soil NO3−-N concentration. Sorbitol and mannitol improved soil nutrient environment, accelerated soil nutrient cycling and had screening and improvement effects on soil microbial communities, while mannitol had greater potential than sorbitol.