Artificial Root Exudates Affect Soil Phosphorus Activation in an Acidic Soil: Role of Phosphorus-Solubilizing Bacteria via RNA Sequencing.

Plant root exudates can effectively activate soil phosphorus (P) through chemical and biological processes. However, the soil P activation resulting from different types of root exudates remains to be clarified, especially in acidic soils with P deficiency. Here, four types of root exudates, including citric acid, malic acid, sucrose, and the mixed root exudate (the mixture of fructose, glucose, sucrose, succinic acid and malic acid), were added to an acidic soil, and available P (AP), alkaline phosphatase (ALP) activity, and phoD-harboring bacterial communities at the DNA (total) and RNA (active) levels were determined. The results indicated that citric acid, malic acid, and the mixed root exudate, rather than sucrose, increased soil AP contents to varying degrees. Four types of root exudates clearly improved soil ALP activities at 6 h of incubation, while only sucrose and the mixed root exudate exhibited improvements at 30 h. Citric acid and sucrose additions significantly improved active levels of the dominant genera Bradyrhizobium at 6 h and Collimonas at 30 h. In conclusion, the diverse root exudates generally demonstrated distinct abilities in activating soil P in the acidic soil, and Bradyrhizobium and Collimonas in response to root exudates mainly contributed to the potential ALP activity.