Phyllotaxy is a key determinant of intraspecific variation in leaf functional traits, with different leaflet positions often representing distinct strategies of resource acquisition and utilization. Yet, the extent to which such phyllotactic differentiation is modulated by ontogenetic stage remains poorly understood. Here, we examined saplings and adult trees of Fraxinus mandshurica, a dominant compound-leaved species in temperate broadleaf forests, by quantifying four leaf economic traits and four stomatal traits across six phyllotactic positions. We further assessed the relative influences of phyllotaxy and environmental factors, including soil total nitrogen, soil water content, and canopy openness, on trait variation at different ontogenetic stages. Our results showed that economic traits varied significantly along phyllotaxy, whereas stomatal traits were relatively conservative. The effects of ontogenetic stage on traits at a given phyllotactic position were trait-specific. Within-group correlations of economic traits and of stomatal traits remained stable across ontogenetic stages and were consistently stronger than between-group correlations. Sapling traits were more strongly affected by soil total nitrogen and soil water content, whereas those in adult trees were primarily shaped by soil water content and canopy openness. Moreover, both trait–trait and trait–environment associations were weaker at the leaflet level than at the compound-leaf level. Our study highlights the critical role of ontogenetic stage in shaping leaf trait responses to phyllotaxy and environmental change, providing new insights into the mechanisms underlying intraspecific trait variation in compound-leaved tree species.

Introduction: Light and soil nutrients are strong drivers of leaf trait variation, but the relative importance in shaping intraspecific trait variation across leaf developmental gradients remains poorly assessed. Previous studies mostly focused on single traits, while fewer have employed multidimensional trait syndromes framework to explore how plants optimize resource use and maintain physiological homeostasis.Methods: We measured leaf economic traits (e.g., specific leaf area, leaf nitrogen concentration) and stomatal traits (e.g., stomatal density, size) in leaflets at different phyllotactic positions of the compound-leaved species Fraxinus mandshurica in temperate forests of Northeast China, while assessing the effects of phyllotaxy and environmental factors (light, soil nutrients) on these traits.Results: We found that (1) specific leaf area and leaf nitrogen concentration significantly increase along the phyllotaxy gradient (from phyllotaxy 1 to 6), while leaf dry matter content, leaf thickness, and stomatal density significantly decrease. No significant variation in the dimensions of economic and stomatal traits was observed across the phyllotaxy gradient; (2) phyllotaxy modulates trait coordination, with decoupled economic and stomatal traits at phyllotaxy 1 but coupled relationships at phyllotaxy 2–6; (3) environmental factors had a greater impact on economic trait dimensions variation, whereas phyllotaxy was more important for stomatal trait dimensions.Discussion: Our study highlights the significance of trait dimensions in understanding plant functional strategies. We emphasize that the influence of environmental factors or phyllotaxy on trait variation is trait-specific, indicating distinct mechanisms for resource acquisition and water use. We recommend considering phyllotaxy when predicting plant responses to environmental changes.

The variation and correlation of leaf economics and vein traits are crucial for predicting plant ecological strategies under different environmental changes. However, correlations between these two suites of traits and abiotic factors such as soil water and nitrogen content remain ambiguous. We measured leaf economics and vein traits as well as soil water and nitrogen content for two different shade-tolerant species (Betula platyphylla and Acer mono) in four mixed broadleaved-Korean pine (Pinus koraiensis) forests along a latitudinal gradient in Northeast China. We found that leaf economics traits and vein traits were decoupled in shade-intolerant species, Betula platphylla, but significantly coupled in a shade-tolerant species, A. mono. We found stronger correlations among leaf traits in the shade tolerant species than in the shade intolerant species. Furthermore, leaf economic traits were positively correlated with the soil water gradient for both species, whereas vein traits were positively correlated with soil water gradient for the shade intolerant species but negatively correlated in the shade tolerant species. Although economic traits were positively correlated with soil nitrogen gradient in shade intolerant species but not correlated in shade tolerant species, vein traits were negatively correlated with soil nitrogen gradient in shade tolerant species but not correlated in shade intolerant species. Our study provides evidence for distinct correlations between leaf economics and vein traits and local abiotic factors of species differing in light demands. We recommend that the ecological significance of shade tolerance be considered for species when evaluating ecosystem functions and predicting plant responses to environmental changes.

Multidimensional trait frameworks are increasingly used to understand how plant functional strategies change across ontogeny. However, whether leaf economic, stomatal, and non-structural carbohydrate traits show consistent or dimension-specific ontogenetic patterns, and how their associations with soil factors vary across ontogenetic stages, remains unclear. We measured 11 leaf functional traits and five soil factors across sapling, young, and adult tree stages of Fraxinus mandshurica in a temperate mixed broadleaf–Korean pine forest. Principal component analysis was used to integrate the measured traits into leaf economic, stomatal, and non-structural carbohydrate axes, whose ontogenetic patterns and stage-specific associations with soil factors were subsequently evaluated. The results showed that the dominant structure of trait covariation shifted from a leaf economic dimension in saplings and young trees to a stomatal size–density dimension in adults. The three functional axes showed distinct stage-specific patterns: scores on the leaf economic axis decreased, and those on the stomatal axis increased from saplings to young trees, with neither differing significantly between young and adult trees, whereas scores on the non-structural carbohydrate axis did not differ significantly between saplings and young trees but were higher in adults. Stage-specific analyses revealed contrasting patterns of soil–trait associations among ontogenetic stages and functional axes, with a broader set of significant associations in saplings and young trees than in adults. Notably, soil water content was the only soil factor associated with all three functional axes in saplings, whereas soil total phosphorus made the largest independent contribution to all three axes in young trees; in adults, only scores on the leaf economic axis were significantly associated with soil pH. Our findings highlight that leaf functional variation is multidimensional, with leaf economic, stomatal, and non-structural carbohydrate dimensions exhibiting distinct ontogenetic patterns, and that soil–trait associations vary among ontogenetic stages and functional axes. These results improve our understanding of variations in multidimensional leaf functional strategies and soil–trait associations across ontogenetic stages.