Using Metabolic Energy Density Metrics to Understand Differences in Ecosystem Function During Drought

Abstract

Terrestrial ecosystems obtain energy in the form of carbon-containing molecules. Quantifying energy acquisition and dissipation throughout an ecosystem may be useful for describing their resistance and resilience to disturbances. Three longleaf pine savannas with different vegetation composition—a result of variation in soil moisture and land use legacy—were used as a case study to test energy-based metrics of ecosystem metabolic function. Available energy from gross ecosystem exchange of CO2 and its dissipation into metabolic energy density (EM) and energy storage were used to identify differences in drought recovery over an 8-year period. Sites with higher plant functional diversity in the understory stored more energy and lowered their EM by ~20% when adapting to drought. In contrast, the site with greater abundance of woody understory and overstory species relied on stored energy twice as often as the more diverse sites. The absence of native understory species, due to anthropogenic legacy, prolonged ecosystem-scale drought recovery by 1 year. This study provides the tools to understand differences in site metabolic energy dynamics and has the potential to identify site characteristics that indicate greater vulnerability to disturbances. Metabolic energy density can be applied to any global ecosystem and provides a first step to describe coupled carbon and energy allocation in ecosystems, which may be used to further refine ecological theory and its management implications.