Fertilization of saplings: growth and hydraulic response of three temperate tree species

Abstract Fertilization plays a crucial role in sapling production and quality, especially in the face of increasing drought frequency driven by climate change. However, its effects on sapling growth and hydraulic traits remain debated, with inconsistent findings across species and conditions. We examined the effects of annual fertilization on growth, gas exchange, and hydraulics of Pinus sylvestris , Fagus sylvatica , and Quercus robur saplings over three years. Fertilization increased sapling growth with species-specific responses. Net photosynthesis (P n ) and stomatal conductance (g s ) increased across species, though with varying timing and magnitude. Hydraulic traits, such as turgor loss point (Ψ tlp ), stem embolism resistance (Ψ 50 ), and drought-induced leaf damage (Ψ EL50 ), were unaffected by fertilization. This suggests limited plasticity in drought resistance traits under well-watered conditions. However, F. sylvatica exhibited increased stem-specific conductivity (k s ) in the final year, indicating species-specific adjustments in water transport. Additionally, fertilization led to a shift in biomass allocation, with reduced root: shoot ratios across all species, raising concerns about potential trade-offs with drought resilience. These findings underscore the importance of species-specific nutrient responses in sapling production and forest management. Further research is needed to assess the long-term effects of fertilization under field conditions, particularly in the context of increasing drought.