Newswise — Recent studies reveal that an increasingly warm climate may transition widely prevalent microbial communities from carbon sinks to carbon emitters, potentially prompting tipping points in climate change. The discoveries are published in the scientific journal Functional Ecology of the British Ecological Society.


  • New research finds that under a warming climate, ocean plankton and other single-celled organisms, known as mixotrophic microbes – can switch from being carbon sinks to carbon emitters.
  • The research also finds that changes in the behaviour of these organisms right before they switch can act as an early warning signal for climate change tipping points.
  • However, increases in nutrient levels in the environment, such as nitrogen from agricultural runoff, can mute these warning signals.

Carbon sinks to carbon emitters

Mixotrophic microbes are versatile organisms capable of transitioning between photosynthetic processes akin to plants, where they absorb carbon dioxide, and consuming activities resembling animals, which result in the release of carbon dioxide. These organisms are widespread on a global scale, commonly inhabiting both freshwater and marine environments. It is estimated that mixotrophic microbes constitute a significant portion of marine plankton populations.

Utilizing a computer simulation that simulated the energy acquisition mechanisms of mixotrophic microbes in relation to warming conditions, scientists from Duke University and the University of California Santa Barbara have discovered that these organisms transition from acting as carbon sinks to becoming carbon emitters as the temperature rises.

These findings indicate that with rising temperatures, these immensely abundant microbial communities have the potential to shift their role from exerting a net cooling impact on the planet to generating a net warming effect.

Dr. Daniel Wieczynski, who is affiliated with Duke University and serves as the lead author of the study, emphasized the significance of their findings by stating, "Our research demonstrates that mixotrophic microbes play a far more significant role in ecosystem responses to climate change than previously recognized. Through their conversion of microbial communities into net carbon dioxide emitters under warming conditions, mixotrophs have the potential to contribute to an acceleration of global warming, establishing a positive feedback loop between the biosphere and the atmosphere."

Dr. Holly Moeller, a co-author of the study and affiliated with the University of California Santa Barbara, emphasized the dual nature of mixotrophic microbes by stating, "Mixotrophs act as 'switches' that have the potential to either mitigate or exacerbate climate change due to their ability to both capture and emit carbon dioxide. Although these microorganisms are minuscule in size, their effects can have significant implications on a larger scale. Models such as the one we developed are crucial for enhancing our understanding of these dynamics."

Dr Jean-Philippe Gibert from Duke University and another study co-author remarked, "Current advanced forecasts of extended climate shifts merely consider microbial activity in an excessively simplified, incomplete, or occasionally inaccurate manner. Consequently, research such as this is crucial to enhance our comprehensive comprehension of the biotic regulations governing Earth's atmospheric mechanisms."

An early warning system

The scientists' framework additionally unveiled that just before mixotrophic microbe communities transition to releasing carbon dioxide, their prevalence begins to oscillate drastically. These fluctuations may be observed in natural settings by tracking the abundance of mixotrophic microbes and provide optimism that these microbes could serve as early indicators of climate change tipping points.

Dr Wieczynski expressed, "These microorganisms could potentially serve as precursory signals for the devastating consequences of swift climate change, particularly in ecosystems such as peatlands that currently play a crucial role as significant carbon reservoirs, wherein mixotrophs thrive abundantly."

Nonetheless, the scientists also discovered that these early warning signals can be dampened by the introduction of elevated nutrient levels, such as nitrogen, into the environment, commonly resulting from agricultural runoff and wastewater treatment facilities.

When higher quantities of these nutrients were incorporated into the simulations, the researchers observed that the temperature range within which the distinctive fluctuations occur begins to contract. Eventually, the signal vanishes entirely, and the tipping point is reached without any discernible warning.

"Detecting these warning signs is going to be a formidable task, particularly when they become more elusive due to nutrient pollution," explained Dr. Moeller. "However, the consequences of overlooking these signals are significant. We could end up with ecosystems in a highly undesirable state, contributing to the emission of greenhouse gases into the atmosphere instead of their removal."

In the study, the researchers conducted simulations spanning a temperature range of 4 degrees, from 19 to 23 degrees Celsius. It is projected that global temperatures will rise by 1.5 degrees Celsius above pre-industrial levels within the next five years and are on track to exceed 2 to 4 degrees by the end of this century.

The researchers emphasize that the mathematical modeling employed in the study is based on limited empirical data to explore the impacts of warming on microbial communities. Dr. Wieczynski remarked, "While models are valuable tools, theoretical outcomes need to be validated through empirical testing. We strongly recommend conducting additional experimental and observational tests to verify our findings."



Journal Link: Functional Ecology