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Tales criaturas unicelulares que se encuentran en lagos y ríos de todo el mundo. Paramecio bursaria puede comer y hacer la fotosíntesis. Dichos microbios desempeñan un papel doble en el cambio climático al liberar o absorber dióxido de carbono, un gas de efecto invernadero que es un importante impulsor del calentamiento, dependiendo de si dependen de estilos de vida similares a los animales o las plantas. Crédito: Daniel J. Wichinski, Universidad de Duke
El aumento de los niveles de calor podría empujar el plancton oceánico y otros organismos unicelulares hacia el umbral de carbono, lo que podría exacerbar el calentamiento global. Sin embargo, estudios recientes sugieren que es posible detectar señales de advertencia tempranas antes de que estos organismos alcancen ese punto crítico.
Un grupo de científicos que estudia una clase de microbios muy extendida pero que a menudo se pasa por alto ha descubierto un circuito de retroalimentación climática que podría amplificar el calentamiento global. Sin embargo, este descubrimiento viene con un lado positivo. también puede ser una señal de alerta temprana.
Usando simulaciones por computadora, investigadores de la Universidad de Duke y la Universidad de California han demostrado que la gran mayoría del plancton oceánico del mundo, junto con muchos organismos unicelulares que viven en lagos, turberas y otros ecosistemas, podrían alcanzar un punto de inflexión. Aquí, en lugar de absorber dióxido de carbono, comienzan a hacer lo contrario. Este cambio es el resultado de cómo su metabolismo responde al calentamiento.
Porque el dióxido de carbono es un gas de efecto invernadero que, a su vez, puede elevar aún más las temperaturas: un circuito de retroalimentación positiva que puede conducir a un cambio drástico, donde una pequeña cantidad de calentamiento tiene un gran efecto.
Pero al monitorear de cerca la abundancia de estos organismos, podemos predecir el punto de inflexión antes de que llegue aquí, informan los investigadores en un estudio publicado el 1 de junio en la revista. ecología funcional.
En el nuevo estudio, los investigadores se centraron en un grupo de organismos diminutos llamados mixótrofos, llamados así porque combinan dos modos de metabolismo:
“Son similares[{» attribute=»»>Venus fly traps of the microbial world,” said first author Daniel Wieczynski, a postdoctoral associate at Duke.
During photosynthesis, they soak up carbon dioxide, a heat-trapping greenhouse gas. And when they eat, they release carbon dioxide. These versatile organisms aren’t considered in most models of global warming, yet they play an important role in regulating climate, said senior author Jean P. Gibert of Duke.
Most of the plankton in the ocean — things like diatoms, dinoflagellates — are mixotrophs. They’re also common in lakes, peatlands, in damp soils, and beneath fallen leaves.
“If you were to go to the nearest pond or lake and scoop a cup of water and put it under a microscope, you’d likely find thousands or even millions of mixotrophic microbes swimming around,” Wieczynski said.
“Because mixotrophs can both capture and emit carbon dioxide, they’re like ‘switches’ that could either help reduce climate change or make it worse,” said co-author Holly Moeller, an assistant professor at the University of California, Santa Barbara.
To understand how these impacts might scale up, the researchers developed a mathematical model to predict how mixotrophs might shift between different modes of metabolism as the climate continues to warm.
The researchers ran their models using a 4-degree span of temperatures, from 19 to 23 degrees Celsius (66-73 degrees Fahrenheit). Global temperatures are likely to surge 1.5 degrees Celsius above pre-industrial levels within the next five years, and are on pace to breach 2 to 4 degrees before the end of this century.
The analysis showed that the warmer it gets, the more mixotrophs rely on eating food rather than making their own via photosynthesis. As they do, they shift the balance between carbon in and carbon out.
The models suggest that, eventually, we could see these microbes reach a tipping point — a threshold beyond which they suddenly flip from carbon sink to carbon source, having a net warming effect instead of a cooling one.
This tipping point is hard to undo. Once they cross that threshold, it would take significant cooling — more than one degree Celsius — to restore their cooling effects, the findings suggest.
But it’s not all bad news, the researchers said. Their results also suggest that it may be possible to spot these shifts in advance, if we watch out for changes in mixotroph abundance over time.
“Right before a tipping point, their abundances suddenly start to fluctuate wildly,” Wieczynski said. “If you went out in nature and you saw a sudden change from relatively steady abundances to rapid fluctuations, you would know it’s coming.”
Whether the early warning signal is detectable, however, may depend on another key factor revealed by the study: nutrient pollution.
Discharges from wastewater treatment facilities and runoff from farms and lawns laced with chemical fertilizers and animal waste can send nutrients like nitrate and phosphate into lakes and streams and coastal waters.
When Wieczynski and his colleagues included higher amounts of such nutrients in their models, they found that the range of temperatures over which the telltale fluctuations occur starts to shrink until eventually the signal disappears and the tipping point arrives with no apparent warning.
The predictions of the model still need to be verified with real-world observations, but they “highlight the value of investing in early detection,” Moeller said.
“Tipping points can be short-lived, and thus hard to catch,” Gibert said. “This paper provides us with a search image, something to look out for, and makes those tipping points — as fleeting as they may be — more likely to be found.”
Reference: “Mixotrophic microbes create carbon tipping points under warming” by Daniel J. Wieczynski, Holly V. Moeller and Jean P. Gibert, 31 May 2023, Functional Ecology.
DOI: 10.1111/1365-2435.14350
The study was funded by the Simons Foundation, the National Science Foundation, and the U.S. Department of Energy.
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