Fine-root dynamics in deeper soils: a critical but overlooked component of ecosystem responses to climate warming.

Climate warming is predicted to strongly affect the functioning of terrestrial ecosystems. The plant root system is a critical component of these ecosystems, with fine roots, in particular, playing a key role in plant water and nutrient uptake and transport. In addition, root litter and exudation represent the dominant plant carbon inputs into soil. Consequently, understanding fine-root responses to warming is essential for predicting how the growth, resilience, and carbon storage of terrestrial ecosystems will respond to future climate change. Despite the growing literature on fine-root responses to warming, most studies have focused on topsoil (0-30 cm). However, a significant portion of the fine-root mass occurs below this depth. For instance, c. 40% of fine-root mass is found below 30 cm in temperate and tropical ecosystems. Due to the importance of fine roots for plants and belowground carbon cycling, focusing solely on surface soils overlooks the critical need for insights into how roots in deeper soil layers (e.g. below 30 cm) respond to warming. We argue that studying the entire soil profile is necessary to comprehensively understand fine-root dynamics under climate warming and the implications for soil organic carbon cycling, water, and nutrient uptake.