Richer Microbial Communities Help Soils Hold Water, Study Finds

Soil is often imagined as an inert sponge, a passive matrix that soaks up rain and releases it slowly to plant roots. A growing body of research is dismantling that picture, and a new study adds a striking twist: the microscopic residents of soil can physically re-engineer the way water moves through it. Researchers at the University of Arizona report in the journal Microbial Ecology that the diversity of a soil microbial community influences how much water a soil can hold and how quickly it loses that water, and that the effect works through the production of extracellular polymeric substances, or EPS, the sticky biochemical compounds microbes secrete around themselves.

EPS is one of the most consequential and least visible materials in terrestrial ecosystems. These substances, a broad class of polysaccharides, proteins, lipids, and nucleic acids released by bacteria and other microorganisms, form the scaffolding of microbial biofilms. In soil, they coat mineral particles, glue them into aggregates, clog and line pore spaces, and alter the wettability of grain surfaces. Because the movement of water in soil is governed almost entirely by pore architecture and surface chemistry, microbial secretions have the potential to shift infiltration rates, evaporation dynamics, and storage capacity. Yet, as the Arizona team notes, the role that microbes and their diversity play in soil hydrology has been severely understudied, leaving scientists with little understanding of whether a richer community can meaningfully reshape the water dynamics of the medium it inhabits.

To test the idea, the researchers constructed sterile mesocosms, controlled soil containers that allowed them to build miniature ecosystems from the ground up. Because the starting material was sterile and inert, any change in the soil’s physical behavior could be attributed to the organisms they introduced rather than to a pre-existing community. The experimental design crossed two factors: microbial diversity, with a high-diversity treatment and a low-diversity treatment, and nutrient availability, with a supplemented treatment and a deficient one. This two-by-two structure let the team disentangle the effect of community richness from the effect of resource supply, which matters because producing EPS is metabolically expensive and requires carbon and nutrients.

The central hypothesis was straightforward: if diversity were artificially manipulated, soil-water properties would shift as a result of EPS production. The researchers predicted that low-diversity systems would have lower functional diversity, which would translate into less EPS production, less moisture storage, and minimal divergence from the inert soil media they started with. In other words, a community with fewer species should have fewer biochemical tools to engineer its environment, while a richer assemblage should contain more complementary producers capable of generating a broader repertoire of polymeric compounds.

The results supported that prediction. High-diversity systems retained more water and lost it more slowly over time than low-diversity systems, a difference the authors attribute to the microbial communities’ altered production of EPS and its knock-on effects on soil structure. The trend was magnified when nutrients were supplied, which is consistent with the metabolic logic of the system: when carbon and nutrients are abundant, microbes can afford the substantial energetic cost of synthesizing and excreting large quantities of polymeric substances, and the hydrological fingerprint of the community becomes stronger.

The team tracked several measures of microhydrology to capture these changes. Water holding capacity was assessed to determine how much moisture the soil could retain, infiltration was measured to see how readily water entered the medium, and evaporation rates were monitored over time to quantify water loss. Alongside these hydrological measurements, the researchers quantified EPS production and soil aggregation, the two soil properties they hypothesized microbes would be altering. This combination of physical and biochemical measurements is what allowed the study to connect a biological variable, community diversity, to a set of physical outcomes that matter for ecosystems: how water arrives, how it is stored, and how it escapes.

One of the most intriguing findings arrived unexpectedly. The researchers observed a correlation between the amount of water retained in the mesocosms and the quantity of lipid EPS produced by the communities. Lipid-rich extracellular substances are known to influence the hydrophobicity of surfaces, and this observation led the team to a provocative conclusion: EPS composition, rather than sheer quantity, may be determinative of a biofilm’s function. If different microbial assemblages produce chemically different cocktails of polymeric substances, then two communities generating the same total mass of EPS could have radically different effects on water behavior. That would make community composition and functional diversity the true levers of soil hydraulic engineering, a hypothesis that future work will need to test directly.

The authors frame these findings as evidence that soil-water traits such as moisture retention are emergent features of the microbiome, properties that arise from the collective activity of many organisms and cannot be predicted from any single species. This perspective has implications well beyond the laboratory. In natural soils, microbial communities are being reshaped by agriculture, pollution, climate change, and land degradation, and if diversity loss degrades the capacity of soils to hold water, then microbial erosion could be quietly undermining drought resilience in ways that conventional soil science has not accounted for. Conversely, the findings suggest that managing microbial diversity could become a deliberate tool for improving soil function.

The potential applications the authors highlight are concrete. If scientists learn how microbes manipulate soil moisture, those functions could be applied to advance sustainable agricultural practices and to enhance ecosystem resilience to water scarcity in arid regions. In drylands, where every increment of water retention matters for crop survival and vegetation cover, inoculating soils with EPS-producing communities or fostering conditions that support diverse microbial assemblages could complement conventional water-management strategies. The work, conducted at the University of Arizona’s School of Plant Sciences with support from the university’s Center for Agroecosystem Research in the Desert, was published open access on October 14, 2026, with Yvonne Kan as lead author and Alonso Favela as corresponding author.

Much remains to be resolved. The mesocosms were sterile, nutrient-manipulated systems, and translating these controlled results into messy field conditions will require studies across real soils, climates, and cropping systems. The mechanisms linking specific EPS chemistries to specific hydraulic outcomes, particularly the role of lipid-rich substances, invite closer biochemical characterization. But the study’s core message stands on its own: the diversity of life in soil is not merely a biodiversity statistic. It is a physical force that changes how water clings to particles, how it percolates downward, and how it evaporates away. In an era of intensifying drought, the microbes beneath our feet may prove to be some of the most important hydrological engineers on the planet, and learning to work with them could reshape how agriculture and conservation approach the world’s drying landscapes.

Subject of Research: How soil microbial diversity affects soil water dynamics through extracellular polymeric substance production

Article Title: Soil Microbial Diversity Alters Microhydrology through Extracellular Polymeric Substance Production

Article References: Soil Microbial Diversity Alters Microhydrology through Extracellular Polymeric Substance Production. (n.d.). https://doi.org/10.1007/s00248-026-02907-y

Image Credits: AI Generated

DOI: 10.1007/s00248-026-02907-y

Keywords: soil microbiome, microbial diversity, extracellular polymeric substances, soil hydrology, water retention, drought, microbial ecology, soil aggregation, biofilms, mesocosms, sustainable agriculture, arid ecosystems