Decadal N and P addition reshapes multi-element allocation patterns and network interaction in subtropical plantation trees

Nitrogen (N) deposition disrupts mineral element dynamics, exacerbating phosphorus (P) limitation and inducing multiple nutrient imbalances. Although P addition is widely adopted to mitigate these negative effects by enhancing P availability, how multi-mineral elements in tropical trees respond to N and/or P addition remains poorly understood, particularly regarding their tissue-specific concentrations and inter-element relationships. Here, we investigated the effects of a decade-long N, and/or P addition on mineral element concentrations across tissues in two typical plantation tree species, Eucalyptus urophylla S. T. Blake (EU) and Acacia auriculiformis A. Cunn. ex Benth. (AA), in southern China. We also examined how these additions altered correlations among elements. Our results showed that both EU and AA maintained stable macro-element levels under long-term N addition, yet experienced significant changes in their micro-elements. This was evident by increased root aluminium (Al) and iron (Fe) concentrations in EU and decreased leaf Fe concentrations in AA. However, tissue-specific responses differed. EU exhibited significant response ratios in root mineral elements, whereas AA had negative response ratios in leaves and branches. Under long-term P and N + P addition, both species accumulated higher P and sodium (Na) but lower potassium (K), with significant response ratios in leaf mineral elements. Crucially, long-term N or/and P addition altered elemental correlation patterns. Specifically, long-term N addition strengthened sulfur (S) interaction with other elements in both species, whereas long-term P disengaged P from other elements in AA, and long-term N + P addition disrupted P interconnectedness in EU. Moreover, long-term N + P addition simplified mineral element network interactions in both species. These shifts in elemental correlations highlight potential cascading effects on ecosystem structure and function. Our findings demonstrate that tropical trees dynamically adjust mineral element concentrations across tissues and reconfigure inter-element relationships in response to N- and P-induced environmental changes. These adjustments have profound implications for nutrient cycling and ecosystem resilience in tropical forests under global changes.