The effect of fertilization on seedling hydraulics

Fertilization is commonly used in forestry nurseries: It helps seedlings also produce more conductive wood (xylem), which increases water transport capacity and in turn growth and productivity. Though, respective adjustments in xylem anatomy may impact the plants` ability to cope with and recover from drought. This project focuses on hydraulic acclimation of Scots pine, English oak and European beech during short- and mid/long-term fertilization and/or drought and on legacy effects after recovery from drought treatment. We hypothesize fertilization to induce increased water transport capacity at the expense of drought tolerance, with lower effects under fertilization combined with drought. We also expect that fertilization-induced changes are species-specific and more pronounced in the long term. In view of climate change causing more frequent and pronounced drought events, knowledge of fertilization effects on plant hydraulics are of great importance.

The Effect of Fertilization on Seedling Hydraulics Fertilization is a widely used technique in forestry nurseries to boost seedling growth and productivity. Fertilization also promotes the development of more conductive xylem (wood tissue), which enhances water transport capacities. However, increased above-ground biomass may enhance a seedling's water demand and thus impact its drought resilience, raising questions about how fertilization affects plant water relations and drought resistance. In this study, conducted at the Department of Botany, University of Innsbruck, fertilization and drought experiments on three important forest tree species (Scots pine, English oak, and European beech) were performed. The hydraulic responses of seedlings to both short- and mid-term fertilization and to repeated drought stress as well as the legacy effects after recovery were analyzed. Experiments demonstrated that fertilized seedlings exhibited more conductive xylem, which led to improved water transport and higher photosynthesis rates. This, in turn, increased growth and productivity. Notably, the effects of fertilization were species-specific and became more pronounced over time. When subjected to drought, fertilized seedlings experienced reduced water transport capacities, reduced leaf CO assimilation, and stunted growth. These adverse effects were particularly severe in seedlings with high levels of fertilization and under extreme drought stress, with variations across species. Fertilization, whether under well-watered conditions or in combination with drought, had minimal impact on embolism resistance. Findings improve our understanding of how fertilization influences seedling hydraulics and their performance under drought conditions and post-drought. Results are a base for developing effective strategies to cultivate drought resilient seedlings for afforestation, which is of importance in the face of climate change. This is also relevant for the Alpine Forest tree species selected in this study as mountain forests, which fulfill important protective function, are especially exposed to global warming.