Slope position mediates the co-utilization of phosphorus by plants and microbes through rhizosphere processes in a phosphorus-limited forest

Phosphorus (P) limitation hinders ecological restoration in vulnerable ecosystems, particularly in forest ecosystems with severe soil erosion. Slope position and rhizosphere effect (RE) are two critical drivers of biological P utilization, but their unknown potential interaction limits the improvement of ecological restoration under P limitation. To bridge this gap, we investigated the interaction on plant–microbe P utilization by quantifying the REs at different slope positions (top, middle, and bottom) of a typical artificial forest on the Loess Plateau, China. The results showed that: (1) most of the positive REs increased by 1.5 to 5.6 times with decreasing slope position, which reversed the resource distribution trend along the slope. (2) Due to nutrient competition, plant and microbial P limitation exhibited contrasting patterns across the slope, both of which were aggravated by the RE on soil nitrogen (N)-P imbalance and litter carbon (C):P imbalance, respectively. (3) Conversely, plant P resorption and the rhizosphere process of microbial P utilization had a synergistic relationship to achieve P co-utilization in the plant–soil–microbe system. (4) The decreasing slope position promoted this P co-utilization by regulating the REs on resource quantities and resource imbalances. Overall, our findings highlight the importance of rhizosphere processes and the mediation of slope position in biological P utilization, further revealing that the rhizosphere-linked synergism of P utilization by plants and microbes may counteract the adverse consequences of P limitation on ecological restoration.