Abstract: Nitrification is a crucial biogeochemical process that regulates soil inorganic nitrogen forms and triggers soil nitrogen losses. While the prevailing paradigm focuses on the role of functional microbial guilds that drive soil nitrification, a clear mechanistic link between tree species and soil nitrification remains to be established in forest ecosystems. With a common garden experiment, we examined the impacts of leaf economics spectrum, tree phenology, and symbiotic fungal associations on soil nitrification across 12 subtropical tree species in January and September. Our results revealed that soil potential nitrification rates ranging from -2.13 to 1.96 mg N kg^-1 d^-1 varied among different tree species. Liquidambar formosana exhibited the highest soil nitrification rate, while Lindera communis and Elaeocarpus decipiens had the lowest soil nitrification rates at both sampling times. Leaf traits were stronger predictors of soil nitrification than soil variables. In particular, acquisitive tree species characterized by greater specific leaf area and lower leaf dry matter content significantly promoted soil nitrification. Deciduous tree species exhibited significantly higher soil potential nitrification rates than those of evergreen tree species. Structural equation models showed that the leaf economics spectrum positively affected litter N content, which in turn increased soil ammonium availability and subsequently promoted ammonia-oxidizing archaea abundance, ultimately facilitating soil nitrification. Taken together, our study demonstrates a leaf trait-based framework for linking tree species to ecological processes and emphasizes that the choice of tree species based on the leaf economics spectrum plays a vital role in predicting ecosystem functioning.

Key words: ammonia-oxidizing archaea, leaf traits, nitrification, resource use strategies, tree species