Droughts are disrupting Earth’s largest carbon storage source

As the world grapples with climate change and its consequences, an often-overlooked aspect of the carbon cycle may hold a key to mitigating some of its effects: soil microbes. Soil stores more carbon than plants and the atmosphere combined, with these microscopic organisms playing a crucial role in the process. 

However, the increasing frequency and severity of droughts, such as those impacting California, could disrupt this delicate ecosystem and have far-reaching consequences for soil health and future greenhouse gas levels.

In a perspective published in the journal Trends in Microbiology, microbial ecologist Steven Allison of UC Irvine warns that if soil microbes adapt to drought more rapidly than plants do, we could face significant consequences. To better manage the situation in both agricultural and natural settings, it is crucial to understand how microbes respond to drought.

“Soil microbes are beneficial, and we couldn’t live without their cycling of carbon and nutrients, but climate change and drought can tweak that balance, and we have to be aware of how it’s changing,” says Allison. 

How soil microbes store carbon

Some soil microbes help store carbon from decomposing plants in the soil, while others release plant carbon back into the atmosphere. The carbon-rich soil has numerous benefits, including improved nutrient retention, increased plant productivity, and erosion prevention.

However, the changing weather patterns in California, characterized by more intense droughts followed by heavier rainfall, can lead to erosion, landslides, mudslides, and sedimentation. 

“From a climate mitigation standpoint, what we want is for more carbon to be in plants and soils and less carbon to be in the atmosphere,” says Allison. Understanding the balance of incoming and outflowing carbon and how it changes with drought, warming, or other climate factors is crucial for managing climate change.

While plants and microbes are both impacted by drought, Allison believes that microbes are more adaptable and can recover faster. Microbes can change their physiology, abundance, and even evolve, which allows them to resist or bounce back from drought more rapidly than plants. 

Potential repercussions if soil balance isn’t restored

However, if more carbon-releasing microbes survive than carbon-sequestering ones, the result could be carbon-depleted soils with negative implications for plant productivity and future greenhouse gas levels.

To nudge the balance in the right direction, Allison emphasizes that more research is needed. “Right now, we have data that suggests that when we have drought, something changes that results in carbon loss, but we don’t understand exactly how or why that’s happening,” says Allison. 

Identifying the microbes most beneficial to plants and most likely to retain carbon in soil could help us tip the balance in their favor.

There is potential to manage or engineer soil microbes to mitigate the effects of drought. In agricultural systems, soil manipulation or the addition of beneficial microbes could be explored. 

In more natural systems, managing plants could indirectly benefit the microbial part of the ecosystem. Furthermore, Allison suggests that more measurements are needed to understand how drought affects soil carbon change in different ecosystems, from the Arctic tundra to deserts.

As climate change continues to threaten ecosystems worldwide, understanding the complex interplay between soil microbes, plants, and carbon could provide valuable insights and solutions for mitigating its impacts.

Earth’s other natural carbon storage mechanisms

Natural carbon storage mechanisms, also known as carbon sinks, play a vital role in the Earth’s carbon cycle by capturing and storing carbon dioxide (CO2) from the atmosphere. These mechanisms help maintain a balance of carbon on our planet and mitigate the impacts of increasing greenhouse gas emissions. Here are some of the major natural carbon storage mechanisms on Earth:

1. Oceans: Oceans are the largest carbon sinks on the planet, absorbing approximately 25% of CO2 emissions generated by human activities. The carbon dioxide dissolves in seawater, forming carbonic acid and bicarbonate and carbonate ions, which are used by marine organisms to build shells and other structures.
2. Forests: Trees and plants absorb CO2 from the atmosphere through the process of photosynthesis. They convert the carbon dioxide into glucose, which they use for energy and growth. As plants die and decompose, some of the carbon is transferred to the soil, while some is released back into the atmosphere through the process of respiration.
3. Soil: Soil is the second-largest carbon sink on Earth, storing more carbon than plants and the atmosphere combined. Carbon is stored in soil as organic matter, which is derived from decomposing plant and animal material. Soil microbes also play a crucial role in transferring carbon from plants to the soil and releasing it back into the atmosphere.
4. Wetlands: Wetlands, including peatlands, swamps, and marshes, store significant amounts of carbon in the form of plant material and soil organic matter. The waterlogged conditions in wetlands slow down the decomposition of organic matter, resulting in the accumulation of carbon over time.
5. Permafrost: Permafrost is the permanently frozen ground found in polar regions and high mountain areas. It contains large amounts of carbon in the form of frozen organic matter. As the climate warms and permafrost thaws, this stored carbon may be released as CO2 or methane, which can exacerbate climate change.
6. Carbonate rocks: Carbonate rocks, such as limestone and dolomite, are formed by the accumulation of carbonate minerals from the shells and skeletal remains of marine organisms. These rocks represent a long-term storage of carbon and can sequester carbon over geological timescales.

These natural carbon storage mechanisms help regulate the Earth’s climate by capturing and storing carbon dioxide. However, human activities, such as deforestation, fossil fuel combustion, and land-use changes, have disrupted the balance of the carbon cycle, leading to increased greenhouse gas concentrations and global warming.

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