Plant economics traits predict plant carbon allocation and responsiveness to arbuscular mycorrhizal fungi under varying precipitation

Most terrestrial plant species form symbioses with arbuscular mycorrhizal fungi (AMF). However, the below‐ground carbon (C) allocation of plants and the nutritional and growth benefits provided by AMF within this symbiosis vary greatly across species and environments. Currently, the extent to which this variation is governed by plant functional trait syndromes remains poorly understood. To address this, we conducted a 13 C pulse labelling study with four grass species inoculated with three AMF species under four precipitation regimes to test whether plant below‐ground C allocation and AMF‐derived benefits can be explained by functional traits representing specific axes of the plant economics spectrum (PES). Our results demonstrate that the two main dimensions of the PES differentially predict the plant–AMF interaction. The first dimension (PC1), strongly aligning with a conservation‐acquisition strategy, was a primary predictor of below‐ground C allocation and its sensitivity to precipitation. The second dimension (PC2), defined by variation in specific root length (SRL) that strongly reflects a collaboration strategy, primarily governed nutrient‐related mycorrhizal responses and their reactions to altered precipitation. Furthermore, path analyses revealed that these traits exert direct and AMF community‐mediated indirect effects on the symbiosis. Synthesis. Our results highlight that species positions along plant economics strategy axes provide a predictive framework for plant C allocation and mycorrhizal responses. By demonstrating that trait–symbiosis coupling is modulated by precipitation, this study advances our ability to predict how plant–AMF interactions respond to environmental change. Read the free Plain Language Summary for this article on the Journal blog.