Abstract: With global ecological restoration advancing, afforestation plays a key role in providing ecosystem services and mitigating climate change. However, intensifying climate change and soil degradation challenge the long-term sustainability of plantations, particularly in nutrient acquisition and utilization. This study focuses on two representative tree species in the Saihanba Forest Farm in China: the cold-tolerant conifer Larix gmelinii var. principis-rupprechtii (Larch) and the fast-growing deciduous broadleaf species Betula platyphylla (Birch). The aim is to analyze their leaf carbon (C), nitrogen (N), and phosphorus (P) stoichiometric characteristics and to reveal species-specific nutrient allocation strategies and their environmental drivers. The results show that Larch exhibited higher C (477.29 ± 11.09 g kg^–1) and P content (1.72 ± 0.12 g kg^–1) than Birch (C: 461.87 ± 12.53 g kg^–1; P: 1.49 ± 0.12 g kg^–1), whereas Birch showed markedly higher C:P and N:P than Larch (P < 0.01). These patterns indicate a relatively conservative, P-enriched strategy in Larch and a more acquisitive, P-limited strategy in Birch. Soil and environmental factors explained 86.58% of leaf stoichiometric variation, with temperature and soil P emerging as the dominant drivers. GAM further revealed strong nonlinear responses: Larch leaf P content increased sharply with soil P (P < 0.01), whereas Birch was more sensitive to climatic factors, reflecting its climate-responsive strategy during rapid growth. These results highlight species-specific environmental constraints and provide empirical evidence for understanding nutrient adaptation strategies under climate change and soil nutrient imbalances, offering valuable insights for forest restoration and nutrient management.

Key words: Leaf stoichiometry, Nutrient use strategy, Environmental drivers, Phosphorus limitation