Understanding processes in deep soils and the subsurface remains a central challenge in Earth system science, limiting prediction of carbon dynamics, hydrologic connectivity, ecosystem resilience, and their representation in models. While observations highlight the importance of deep critical zone processes, experimental tests of underlying mechanisms remain rare due to limited access and control.

A new generation of experimental systems including ecotrons, deep soil mesocosms, lysimeter arrays, and hybrid field–laboratory platforms are enabling controlled manipulation across depth and time. These systems integrate advanced sensing, imaging, and environmental control, supporting hypothesis-driven experiments and model evaluation.

This session invites contributions that use or develop such systems to advance mechanistic understanding and prediction of subsurface processes. Topics include deep soil carbon and nutrient dynamics, hydrologic flowpaths, plant–microbe interactions, novel imaging approaches, and microbial function (e.g., carbon use efficiency, signaling, VOCs) regulating biogeochemical feedbacks across depth.

• A - Atmospheric Sciences
• GC - Global Environmental Change
• H - Hydrology