Slope Position Mediates the Co-Utilization of Phosphorus by Plants and Microbes Through Rhizosphere Processes in a Phosphorus-Limited Forest

Abstract

Phosphorus (P) limitation hinders ecological restoration in vulnerable ecosystems, particularly in severely eroded forests. 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) in a typical artificial forest ( Robinia pseudoacacia ) of 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) Plant and microbial P limitation exhibited contrasting patterns due to nutrient competition (standardized slope = –0.746, P < 0.001), and they were aggravated by the RE on soil nitrogen (N)-P imbalance and litter carbon (C):P imbalance, respectively. (3) In contrast, 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 (standardized slope = 0.729, P < 0.001). (4) The decreasing slope position promoted this P co-utilization by regulating the REs on resource quantities and resource imbalances. Overall, our findings highlighted the importance of rhizosphere processes and the mediation of slope position in biological P utilization, further revealing that the synergism of P utilization by plants and microbes through rhizosphere processes may counteract the adverse consequences of P limitation on ecological restoration.

Keywords: Slope position, Rhizosphere effect, Phosphorus utilization, Resource imbalance, Plant-microbe interaction, ecological stoichiometry