Simulated root exudates stimulate the abundance of Saccharimonadales to improve the alkaline phosphatase activity in maize rhizosphere

Plants promote the mineralization of soil organic phosphorus by secreting phosphatase into the rhizosphere, in addition they promote the growth of bacteria which also release phosphatase to the rhizosphere. Sugars are the main component of root exudates and a key driver of soil microbial activity. In this study, we added different concentrations of a range of sugars found in root exudates to the soil during maize growth to investigate whether sugars could stimulate alkaline phosphatase activity. Sugars increased alkaline phosphatase activity in soil, while different sugars increased this activity to different extents. Small concentration of sugars did not stimulate alkaline phosphatase activity in the rhizosphere, change the bacterial community structure or select phosphatase producing species such as Saccharimonadales. However, alkaline phosphatase activity was enhanced by larger concentration of added sugars, which increased indigenous soil Saccharimonadales abundance. Notwithstanding this, Saccharimonadales were rare in the microbial taxa at the order level and their relative abundance was only 2.1%–4.9% at different sugar concentration levels. Our results suggest that addition of sugars selected for indigenous soil Saccharimonadales, enhancing alkaline phosphatase activity in the rhizosphere. These rare microbial taxa may be a key species in soil phosphorus cycling.