Plant-soil feedback drivers are context-dependent but maintain stable competitive hierarchies in a changing climate

Plant-soil feedback (PSF) plays a critical role in plant species coexistence and community assembly, but it remains unclear whether its patterns and underlying drivers are influenced by changing environmental conditions. Here, we used an existing PSF field experiment in which plant communities with different functional groups (i.e. legumes versus grasses) and different growth strategies (i.e. deep roots versus shallow roots) were allowed to condition the soil more than four years over two sites with distinctly different precipitation regimes, respectively. In the feedback phase, we conducted a controlled greenhouse experiment using conditioned soils collected from both sites, and subsequently sown with the response plant community. Our results showed that both the strength and direction of PSF differed significantly between the moister and drier sites, with stronger negative feedback in the drier site. Plant-soil feedback was positively correlated with relative yield and competitive ability of species, thereby serving as an important driver of competitive outcomes. This competitive hierarchy among the grassland species was as follows: M. sativa > B. inermis > L. chinensis > M. ruthenica . More importantly, PSF intensity and its drivers were highly dependent on the environmental conditions. At the drier site, the soil fungal community was a key predictor of PSF intensity, whereas soil ammonium availability emerged as a key predictor in variable importance analysis at the moister site. Overall, our findings emphasize the role of regional environmental conditions in determining the mechanisms through which soil legacies regulate plant growth. This context-dependency of PSF underscores the critical need to integrate environmental variation into feedback models, which is essential for improving predictions of plant community dynamics under future climate change. • We combine four-year soil conditioning at two sites with a greenhouse experiment. • Plant-soil feedback is stronger at the drier site than at the moister site. • The competitive hierarchy among four plant species remains stable at both sites. • Drivers of plant-soil feedback are strongly shaped by environmental conditions.