Root acquisitive traits mirror the functional modules of root-associated fungi

The interactions among soil microbiota can be indicated by co-occurrence network analysis. The root-associated and soil-associated fungal networks are likely to be influenced by aboveground energy and belowground resources supplies. Most studies have focused on the role of soil nutrients in driving the network, yet the root's role remains elusive. Here, we chose a pure larch forest plantation to control the tree species, age, and soil nitrogen, collected more than 8000 root tips, quantified six root traits, and investigated the compositions of root and rhizosphere soil fungal communities, and network modules across 27 plots. We found that each root tip harboured distinctive fungal species interactions, even in the same tree with a similar age and soil nitrogen. Root-associated fungal OTUs accounted for 14% of soil-associated fungal OTUs, and they only formed a few functional modules, which correlated with three key resource-related root traits: root branching intensity, specific root length, and root diameter. Forest age, linked with root traits, exerts a greater role than nitrogen addition in constraining the complexity and stability of fungal interactions. In contrast, the rhizosphere soil fungi showed complex interactions and formed nearly 120 modules, and several of the key soil fungal modules (higher relative abundance) were influenced by soil nitrogen and phosphorous availability. These results demonstrated that root acquisitive traits are the central factors influencing the root-associated fungal interactions, with a systematic co-varied phenomenon in the root acquisitive traits-microbe functional modules across a wide range of soil nitrogen levels.