Small-scale experiments in diverse ecosystems highlight the intricate linkages between microbial behavior and ecosystem-scale processes

Background/Question/Methods

Microorganisms are responsible for a host of processes that drive soil organic matter decay and production, nutrient cycling, and resource loss via leaching and gaseous emissions from ecosystems.  Upscaling microbial responses to environmental change across time and space is important for ecosystem process models, but microbial processes only rarely lend themselves to such efforts.  Historical environmental conditions shape microbial community structure, function and response to perturbation on timescales of years, months, and hours. Steep biogeochemical gradients across space also influence microbial communities, whose behavior can provide a positive feedback that maintains spatially distinct microbial functional zones.  We present data describing microbially mediated biogeochemical fluxes from diverse ecosystems that highlight the intricate interactions between life and Earth’s abiotic realm that help maintain our planet’s climate, and the challenges of upscaling microbial behavior across time and space. 

Results/Conclusions

Puerto Rican soil microbes pre-exposed to drought in the preceding year maintain more consistent community composition and exo-enzyme activities during subsequent drought, relative to drought-naïve microbes.  In grassland and boreal forest soils, changing temperature and [O₂] can quickly amplify or even reverse biogeochemical outcomes across hours and months, such that a soil with closely matched N₂O and N₂ production quickly exhibits persistent net N₂O emissions, and a low N₂O emitting soil can emit the most N₂O.  At the Calhoun Critical Zone Observatory, deep root decay has generated O₂-starved microsites where CH₄ generation is robust; mm away, relatively O₂-rich microsites promote net methanotrophy.  Responses of CH₄ and N₂O fluxes to moisture in Puerto Rican soils vary as much within a single forest in sign and magnitude as across a range of tropical forests. We categorize challenges for generalizing microbially-driven biogeochemistry across time and space, and clarify research needed to aid these efforts.  To celebrate ESA’s 100^th anniversary, we highlight how studies quantifying interactions between some of life’s smallest actors and the biogeochemical cycles that maintain life on Earth help embody Arthur Tansley’s original vision of ecosystem ecology.