Effect of urban pavement on nutrient strategies of common greening tree species in northern China

There are many factors that affect how urban tree species absorb and use nutrients, but little is known about the impact of pavement in urban areas. In this study, we selected four common urban tree species-Platanus x acerifolia, Metasequoia glyptostroboides, Robinia pseudoacacia, and Pinus thunbergii-and three pavement coverage categories-unpaved, semi-paved, and fully paved-in Qingdao, a typical city in northern China, to investigate changes in the leaf nutrient utilization strategies of tree species in paved environments. The nitrogen (N) resorption efficiency (NRE) and phosphorus (P) resorption efficiency (PRE) of R. pseudoacacia and the NRE of M. glyptostroboides increased in semi- and fully paved environments. Additionally, the N resorption proficiency of M. glyptostroboides increased significantly with pavement coverage, indicating that the biochemical limitation on N resorption was weakened. Similarly, the contents of N, P, and potassium (K) in R. pseudoacacia and N and K in M. glyptostroboides significantly increased with pavement coverage. This indicates that R. pseudoacacia, a nitrogen-fixing Fabaceae tree species, and M. glyptostroboides, a deciduous Cupressaceae tree species, can better adapt to pavement in urban settings, and even high pavement coverage levels can induce higher nutrient contents and resorption capacities. In addition, M. glyptostroboides showed potentially poor adaptability for N, P, and K uptake in the more stressful pavement environments, and P. x acerifolia showed relatively poor adaptability in P-limited environments. Robinia pseudoacacia associates with nodule-forming nitrogen-fixing bacteria, thus retaining more N in its leaves and showing a low NRE. These findings not only provide additional insight into tree growth at varying pavement coverages but also preliminary guidance for tree species selection to promote resilience in urban areas.