Root exudation of hazelnut saplings in response to soil water limitation

The impact of drought on the rhizosphere is largely unknown, but understanding and leveraging soil-plant responses to climatic stress could represent a key strategy to increase plant resilience, adapt agricultural systems, and protect ecosystems in a changing climate. Root exudation, the release of organic molecules from roots into rhizosphere soil, is a critical process that mediates plant-soil-microbe interactions, shaping plants’ stress response, carbon (C) allocation, and survival. The effect of soil water stress on root exudation is not well understood across crop species; however, it appears that moderate stress stimulates exudation rates, increases root C allocation, and shifts exudate composition. Our greenhouse experiment investigates the rate of root exudation in hazelnut plants—an emerging woody perennial crop globally—under both well-watered and drought conditions. First, we adapted the Phillips et al. (2008) exudation collection methodology to sample exudates from hazelnut saplings in a greenhouse setting. This thorough investigation made clear that different methodological collection parameters greatly impact exudate results. With this information, we decided on a collection method that balanced scientific best practices and practical considerations. We then began the water stress experiment by randomly assigning 12 hazelnut saplings to either water-stressed or well-watered treatments. We measured exudate concentration using a Shimadzu TOCL. Additionally, we took images of the measured roots to analyze the relationship between root physiological parameters and exudation. We observed that water stress increased exudation rates. Combined with plant physiological and water stress data, increased exudation indicates a greater C allocation to below-ground root systems during water stress. Our results show a strong relationship between root parameters (i.e., number of root tips) and exudation. This research helps improve our understanding of root exudation as a potential mechanism for enhancing plant drought resilience, offering insights into plants’ adaptive strategies that could support sustainable agricultural systems in a changing climate.