Soil provides a variety of services that are indispensable to life on Earth. The global decline in soil quality is therefore a major concern. One solution may lie in the hands of tiny organisms that can direct ecosystem recovery: microorganisms. They are so small that they cannot be seen by the naked eye, but they can make a big difference to restoring soils and ecosystems. This is argued by scientists from Wageningen in the scientific journal Science.
Microorganisms, such as fungi and bacteria, are indispensable for the soil. They determine how plants can take root, suppress plant diseases and break down dead plant material, from which new nutrients for plants arise. They also determine the sponge function of the soil: for example, how much water is filtered and retained. Because of their indispensable function, microorganisms are often seen as indicators of soil health. Less attention is paid to their potential as directors of soil recovery. Scientists at Wageningen University & Research emphasize the importance to change this.
Gamechangers
They say microbiota, the collective name for all types of microorganisms, are the 'game changers' in soil recovery. To get a better idea of how far this potential reaches, the authors have made an overview of the most promising microbial groups. In doing so, they also indicate how each group can help in different forms of restoration.
"That microorganisms determine soil functions has been known for at least two decades," says Oksana Coban, microbiologist and lead author of the Science study. "Yet there are hardly any experiments that look at how microorganisms can influence soil properties in such a way that they can help degraded soil ecosystems (ecosystems that have declined in quality)." This idea arose during an Open Mind project of NWO. Coban: "I went into that with an open mind. As a microbiologist, soil restoration was a new topic for me, but I was surprised how little is known in this area."
Hydrological restoration
The study pays special attention to so-called hydrological restoration. This involves the sponge effect of the soil: allowing enough water to infiltrate while retaining some for plants. Water is needed for plant growth, which in turn is an essential step for the recovery of degraded soils. "Although only 0.05% of the world's freshwater supply is stored in soil, soil water is essential for life on land," explains co-author Martine van der Ploeg. "The interaction between soil biology and the sponge effect of the soil plays an essential role in the water cycle. This also requires cooperation between soil biologists and hydrologists. This is rare so far and therefore makes this study very unique."
In the overview of most promising microbial groups for soil restoration, the authors start with the most promising groups for hydrological soil restoration. The data are the result of an in-depth analysis into the composition of microbiota in drylands and how they respond to changes in soil water. Using this information, it was possible to stimulate the growth of microbiota by adding "food" that they love and in this way improve the sponge action of the soil. Once the health of the soil is sufficiently improved, it is possible to add vegetation that will work together with microorganisms to further strengthen the soil.
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MARCH 3, 2022
Dead or alive: Microorganisms in soil shape the global carbon cycle
by Lawrence Livermore National Laboratory
Composition of the soil microbiome and its role in organic matter cycling in different soil habitats.
Credit: Nature Reviews Microbiology (2022). DOI: 10.1038/s41579-022-00695-z
Whether dead or alive, soil microorganisms play a major role in the biogeochemical cycling of carbon in the terrestrial biosphere. But what is the specific role of death for the bacteria, fungi and microfauna that make up the soil microbiome?
That is the topic of a new review by Lawrence Livermore National Laboratory (LLNL) scientists and collaborators. The article, appearing in Nature Reviews Microbiology, describes how living and dead microorganisms strongly influence terrestrial biogeochemistry by forming and decomposing soil organic matter—the planet's largest terrestrial stock of organic carbon and nitrogen, and a primary source of other crucial macronutrients and micronutrients.
By shaping the turnover of soil organic matter, soil microorganisms influence atmospheric concentrations of CO2 and the global climate, as well as help provide crucial ecosystem services like soil fertility, carbon sequestration, plant productivity and soil health.
"Our new understanding of how organic matter cycles through soil emphasizes the importance of both living and dead microorganisms in forming soil organic carbon. It is increasingly possible to leverage this understanding within biogeochemical models and to better predict ecosystem functioning under new climate regimes," said LLNL scientist Noah Sokol, lead author of the paper.
The soil microbiome is the most diverse community in the biosphere, holding at least a quarter of Earth's total biodiversity. Tens of millions of species of bacteria, archaea, fungi, viruses and microeukaryotes coexist below ground, although only a few hundred thousand have been characterized in detail. A single gram of surface soil can contain more than 109 bacterial and archaeal cells, trillions of viruses and tens of thousands of protists. But the soil microbiome's influence on biogeochemistry extends well beyond the metabolic activities of living organisms.
"Dead microorganisms accrete in soil as their cellular remains stick to the mineral matrix. Their dead biomass can make up as much as much as 50% of the soil organic matter pool. This means that dead microbial biomass in soil is one of the largest stocks of organic carbon on the planet," said Jennifer Pett-Ridge, LLNL project lead and head of the Department of Energy's Office of Science "Microbes Persist" Soil Microbiome Scientific Focus Area (SFA).
New advances in DNA sequencing and isotope tracing are allowing the LLNL team to understand the unique attributes of soil microbes—even those that cannot be cultivated in the laboratory. Though analysis of genetic and biochemical signatures, the team can infer the ecological relationships that control who live, and who die, in complex soil food webs.
Because soil microbial necromass (organic material consisting of, or derived from, dead organisms) represents one of the most globally significant pools of carbon and other nutrients, the authors report that the mechanism and rate of microbial death likely impact terrestrial biogeochemical cycling—an idea they are currently testing in a suite of experiments that are part of LLNL's Soil Microbiome SFA. The SFA team also is establishing experiments to study how different traits of microorganisms affect organic matter cycling in soils. Team members are working to integrate this trait-based approach into models that predict soil biogeochemical dynamics and enhance the ability to predict changes to the global carbon cycle.
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