The effects of fine roots and arbuscular mycorrhizal fungi on soil macropores

Soil macropores are crucial to assess soil stability and control erosion as an essential component of soil structure. The variations in soil macropores with vegetation succession remain largely unclear, and the regulatory mechanism is still poorly understood. Plant fine roots and arbuscular mycorrhizal fungi (AMF) have been supposed to be dominant determinants of soil structure, but their separate effects on soil macropores remain underappreciated, let alone the effects of their interactions. This study used quantified imaging techniques to explore the effects of plant fine roots and AMF on soil macropores along a 55-year vegetation restoration chronosequence on the Loess Plateau. We found that soil macropore properties, such as macroporosity, connectivity, fractal dimension, and tortuosity, were all significantly improved with vegetation succession. Fine root density properties significantly increased, whereas morphological properties decreased along the restoration chronosequence with a shift to a conservative root resource usage strategy. Furthermore, duration of vegetation succession had a positive effect on AMF community structure and mediated the root chemical properties indirectly. Plant fine roots affected macropores directly with the positive effects of root density properties, whereas the morphological properties and chemical properties had negative effects. By comparison, the influence of the AMF community structure (i.e., AMF species composition) on macropore features was indirectly mediated through root chemical properties. Overall, this study investigated how plant fine roots and AMF separately and/or jointly affected soil macropores via direct and indirect mechanisms. Thus, this study may greatly contribute to restoration by assisting vegetation configuration to improve soil structure and enhancing the ecological function of afforestation.