Root Foraging Alters Global Patterns of Ecosystem Legacy From Climate Perturbations

• Published in: Journal of geophysical research. Biogeosciences Vol. 127; no. 4
• Main Authors: Berkelhammer, M., Drewniak, B., Ahlswede, B., Gonzalez‐Meler, M. A.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-04-2022; American Geophysical Union (AGU)
• Subjects: Aridity; Atmospheric models; Climate; climate extremes; Climate models; Critical components; Drought; Earth System Models; ecosystem legacy; Ecosystem recovery; Ecosystems; Evapotranspiration; Foraging; land surface models; Mineral nutrients; Nutrients; Perturbation; Perturbations; Primary production; Recovery; Recovery time; Roots; Simulation; Terrestrial ecosystems; Time; Vegetation; Water stress
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2021JG006612

The response of terrestrial ecosystems to climate perturbations typically persist longer than the timescale of the forcing, a phenomenon broadly referred to as legacy. Understanding the strength of legacy is critical for predicting ecosystem sensitivity to climate extremes and the extent that persistent changes in surface‐atmosphere exchange might feedback onto climate. The cause of ecosystem legacy has been associated with myriad factors such as changes in aboveground biomass, however, few studies have tested how changes in the depth distribution of fine roots in response to perturbation might alter an ecosystem's recovery time. We explore this question using an Earth System Model that includes a dynamic root module where vegetation can forage for water and nutrients by altering their root profiles. The global simulations presented here 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 and is thus unfavorable. The simulations show that while the inclusion of dynamic roots might only minimally affect global patterns of Gross Primary Productivity and Evapotranspiration, the shift in root profile alters the timescale of recovery. Studies interested in the sustained response of land surfaces fluxes to climate disturbances should consider models that include dynamic root capability.
Plain Language Summary
When vegetation is stressed from climate events such as drought, they alter the depths where roots are developed. This allow plants to better access resources that have become limited—typically water. Most Earth System Models do not include this dynamic and instead use a fixed root profile. It is unclear how the absence of dynamic roots affects the skill at which these models capture the response and recovery to climate stress events. Here, we use a climate model with dynamic roots to see how the presence of foraging roots affects the way different ecosystems respond to drought. We show that in drier ecosystems, vegetation develop deeper roots after drought and this allows the vegetation to recover more quickly from drought. Wetter ecosystems also develop deeper roots in response to stress, however, this actually slows down their rate of recovery. Ecosystem response to drought is a critical component of climate models and we show that models that lack dynamic roots miss a key component of terrestrial ecosystem recovery from stressful climate events.
Key Points
Drought and pluvial events lead to shifts in root profiles as vegetation forages for water or other limited resources
Earth System Model (ESM) simulations that include a dynamic root profile were used to assess how root dynamics influence ecosystem legacy
Dynamic roots enable semi‐arid (wet) ecosystems to recover more quickly (slowly) from perturbation, an effect not included in most ESMs