Root foraging alters global patterns of ecosystem legacy from climate perturbations

The response of terrestrial ecosystems to climate perturbations typically persist longer than the timescale of the forcing, a phenomenon that is broadly referred to as ecosystem legacy. Understanding the strength of legacy is critical for predicting ecosystem sensitivity to climate extremes and the extent to which persistent changes in land surface-atmosphere exchange might feedback onto the climate, for example, extending drought. The cause of ecosystem legacy has been tied to numerous factors such as changes in leaf area index, however, few studies have tested how changes in root profiles in response to stress might alter an ecosystem's recovery time. We utilize an Earth System Model that includes a dynamic root module where vegetation can forage for water and nutrients by altering their root profiles. As expected, the simulations show that in response to water stress events most ecosystems deepen their root profiles. In semi-arid ecosystems, this response expedites recovery (i.e. less legacy) relative to simulations without dynamics roots because access to deeper water pools after the initial event remains favorable. In wetter ecosystems, the development of deeper root profiles slows down the recovery timescale (i.e. more legacy) because the deeper root profile reduces access to nutrients. The recovery of hyperarid systems is also delayed presumably to the loss of shallow roots and ability to access water from smaller rain events. The results show that the response of root profiles to external forcing is a critical component of global patterns of legacy that is not typically represented in Earth System Models.