Xylem anatomy differentiation explains coordinated variation of economic and hydraulic traits in urban tree species

Urban drought increasingly challenges the survival and performance of urban forests, consequently undermining their sustainability and productivity. Hydraulic-economic trait trade-offs are primary determinants of species drought tolerance, yet these trade-offs remain poorly understood in urban forests. In this study, we investigated the differentiation in hydraulic and economic traits in leaf and stem functional traits among 14 tree species with different xylem anatomical types, explored their correlations along the plant economic spectrum, and further systematically evaluated drought adaptation strategies, aiming to guide species selection and management in urban forests. We found that ring-porous trees exhibited trait values associated with faster water transport compared to diffuse-porous species. Specifically, ring-porous species had significantly higher xylem-specific conductivity, leaf-specific conductivity, and branch xylem vessel diameter. However, the hydraulic safety margin of diffuse-porous species was significantly lower than that of ring-porous species, accompanied by lower leaf and wood phosphorus content. These patterns support the hydraulic safety enhancement strategy in ring-porous species. Across the 14 studied tree species, ring-porous species occupied the fast-acquisitive end of the plant economics spectrum, while diffuse-porous species were positioned at the conservative end. We also discovered a significant negative correlation between hydraulic and economic functional trait principal components, demonstrating that hydraulic safety and carbon economy are synergistically integrated along a unified plant economics spectrum, from fast-growing but vulnerable species to slow-growing but resilient ones. Our study reveals that ring-porous and diffuse-porous species occupy opposite ends of the plant economics spectrum, employing divergent drought adaptation strategies. This clear functional differentiation provides a robust ecological rationale for diversifying urban forests. We propose that selecting a mixture of acquisitive and conservative species will create a more resilient urban ecosystem capable of withstanding a variety of environmental stresses, from seasonal droughts to heatwaves, thereby securing long-term stability and functionality.