Positive allelopathic effects of <i>Cornus controversa</i> litter on soil phosphatase activity and seedling growth in the endangered tree <i>Davidia involucrata</i>

Allelopathic interactions between associated tree species can shape seedling establishment, resource acquisition, and long-term coexistence. However, the mechanisms underlying such interactions in endangered plants remain underexplored. In this study, we aimed to elucidate whether and how aqueous litter extracts from Cornus controversa Hemsl. influence the growth performance and nutrient acquisition in Davidia involucrata Baill., a relict and endangered tree species in China. Seedlings were treated with distilled water (control), branch litter extract, leaf litter extract, or a mixture of both at natural concentrations. Across all treatments, litter extracts increased plant height, total leaf area, dry mass, and tissue nitrogen (N) and phosphorus (P) content, with branch litter extract exerting the strongest growth-promoting effects. Notably, this treatment was associated with a marked increase in soil phosphatase activity, while root phosphatase activity remained unchanged. Soil phosphatase activity showed significant positive relationships with most growth traits of D. involucrata seedlings. Metabolite profiling identified 35 shared compounds and multiple organ-specific metabolites among the extracts, with branch litter extracts exhibiting the highest abundance of indole-related compounds, suggesting a potential biochemical basis for the observed positive allelopathic effects. These findings reveal a previously underappreciated positive allelopathic interaction involving an endangered tree species and demonstrate that organ-specific litter inputs can enhance nutrient acquisition by activating soil enzymes. This study offers novel mechanistic insights into how associated tree species may sustain ecological interactions under nutrient-limited conditions, with implications for the conservation and management of endangered forest species.