Abstract: Urban forests are highly multifunctional and provide numerous ecological functions. Plant functional traits individually or jointly influence the ecological multifunctionality of tree species (TS-EMF) and can also modify TS-EMF in response to environmental changes. However, there has been limited exploration of multitrait combinations for predicting TS-EMF across seasons and of trait thresholds that enhance TS-EMF. Here, for 10 dominant tree species in urban forests of Northeast China, 14 traits were measured and four aboveground and three belowground ecological functions assessed in three seasons. Ecological functions and TS-EMF differed significantly throughout the seasons (P < 0.05). Synergistic relationships were found between carbon sequestration and oxygen release, between cooling and humidification, and between organic carbon accumulation and nutrient cycling. Notably, aboveground multifunctionality played a leading role in TS-EMF. With seasonal changes, resource allocation shifted toward traits related to resource acquisition rather than conservation to maintain TS-EMF. The combination of traits that predicted TS-EMF varied by type, accounting for up to 66.45% of the variation. TS-EMF was primarily driven by leaf structure in spring and by nutrient accumulation in autumn. Leaf carbon content (LCC) consistently served as a stabilizing factor for predicting TS-EMF across seasons. At 36.5–36.8 mg g^–1, LCC had its optimal effect on TS-EMF. Other traits in combination that positively influence total TS-EMF include leaf nitrogen content (3.43–3.45 mg g^–1), leaf phosphorus content (0.80–0.83 mg g^–1), and leaf area (65.86–68.43 cm²). Within these specified trait thresholds, Morus alba and Quercus mongolica were identified as key species. These findings suggest that the trade-off between various ecological functions can be managed by altering plant traits across seasons. This approach could provide a theoretical foundation for enhancing the TS-EMF of urban forests through trait-based management, offering practical guidance for selecting tree species.

Key words: Ecological multifunctionality of tree species, Traits combination, Urban forests, Leaf carbon content