Progress and future directions of biogeographical comparisons of plant-fungal interactions in invasion contexts

Plant invasions are biogeographical phenomena that may involve shifts in belowground plant-fungal interactions, such as the release from fungal pathogens or more beneficial interactions with mutualists in nonnative ranges. However, native and nonnative ranges are not uniform but environmentally heterogeneous, and plant-fungal interactions are strongly shaped by spatio-environmental context. Intense discussion at the 45^th New Phytologist Symposium revealed that we lack information on how well spatio-environmental variation within ranges has been considered in samplings and analyses of studies comparing plant-fungal interactions between ranges. Through a systematic review, we assessed the sampling quality of recent biogeographical studies. We found that the majority relied on a limited population sampling within each range, often covering only a small fraction of the species' spatial distribution and macroclimatic niche. Additionally, low similarity between the sampled climatic gradients in the native and nonnative ranges might have introduced false-positive differences across ranges. These sampling deficiencies may undermine the robustness and representativeness of range comparisons, thereby restricting our ability to accurately assess the role of plant-fungal interactions in invasion success. We recommend that future research incorporate broader and more comparable spatio-environmental variation in both ranges, and we provide practical guidelines for improving sampling designs.