Effects of long‐term nitrogen addition on two dominant species in a drought‐prone Mediterranean forest

This study aimed to assess the long‐term effects of nitrogen (N) addition on recruitment, growth, survival, and physiological responses in Quercus ilex and Phillyrea latifolia , two codominant species typical in the Mediterranean forests. Here, we present a 9‐year N addition experiment (20 kg N ha −1 year −1 , δ 15 N‐enriched) in an N‐limited, drought‐prone Mediterranean forest. We show that Q. ilex recruitment increased 19‐fold under N addition, whereas P. latifolia recruitment declined sixfold. In the denser forest stands, N addition under no water stress increased the total basal area for both species, with greater increments for Q. ilex with a 32% growth increase. Survival analyses revealed a size‐dependent mortality risk, with smaller stems exhibiting 13‐fold (for Q. ilex ) and twofold (for P. latifolia ) higher mortality rates, yet independent of N addition. Physiologically, under N addition both species increased their photosynthetic potential but Q. ilex experienced a significant decline in leaf water potential, suggesting increased vulnerability to hydraulic failure. Foliar δ 15 N enrichment was observed only under high water availability, indicating enhanced N uptake efficiency under these conditions. These findings suggest that N addition might shift species composition in Mediterranean forests, favoring Q. ilex but increasing its physiological stress under projected aridification. Our results highlight species‐specific effects of N addition and water stress, which should be prioritized to inform adaptive forest management.