Neighborhood tree diversity alleviates soil magnesium limitation via optimized foliar resorption and transpiration-driven uptake

Plant diversity is known to enhance soil resource availability and productivity through niche partitioning and facilitation; however, existing studies have predominantly examined these effects at the community level. The role of tree neighborhood diversity in alleviating nutrient limitations remains unclear. Here, using a tree diversity experiment in a subtropical forest with naturally low phosphorus (P) availability and depleted soil base cations, we evaluated how neighborhood diversity helps alleviate nutrient co-limitation. We found that greater neighborhood phylogenetic and trait dissimilarities enhanced growth rates and increased foliar P and magnesium (Mg) concentrations, as well as resorption efficiency in focal trees. Foliar Mg exhibited a more pronounced response than P and calcium (Ca), suggesting that diverse communities may prioritize alleviating Mg limitation over other nutrient limitations. Elevated foliar Mg concentration in focal trees were positively correlated with foliar transpiration, both driven by greater neighborhood phylogenetic dissimilarity. Our findings demonstrate that neighborhood diversity is essential in mitigating nutrient limitations on tree growth, highlighting the importance of phylogenetic and functional trait dissimilarities in mediating these positive effects.