Soil also suffers from heat waves: organic waste used to boost its tolerance to 50 degrees Celsius
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Researchers Sana Boubehziz and Antonio Sánchez Rodríguez from the Edaphology group within the Department of Agronomy (University of Cordoba) analyzing soil samples in the laboratory
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Credit: University of Cordoba
The successive heat waves that sweep across southern Spain in summer have harmful effects on the entire community that lives there, from humans to the microbes that inhabit the soil. Both share an impressive resilience that has enabled them to survive and adapt, each in its own way, to successive episodes of extreme temperatures. But that adaptability has its limits. And when the temperature exceeds 40 degrees, just as human health suffers, the microorganisms that inhabit the soil—and from there provide a multitude of ecosystem services, such as carbon sequestration and plant nutrition—concentrate more on survival than continuing their work.
A study conducted by the University of Córdoba (UCO) in collaboration with the School of Environmental and Natural Sciences at Bangor University in the United Kingdom has determined the temperature limit that soil in various Mediterranean regions can reach before it begins to degrade. The study also provides insights into what we can do to help the soil. Above 40 degrees, microorganisms' ability to capture carbon diminishes, and it practically "shuts down" at 50 degrees— a temperature to which the calcareous soils of the province of Córdoba are often exposed. The higher the temperature they endure, the lower the soil's phosphorus reserve becomes, which is virtually non-existent when exposed to temperatures above 40 degrees.
To address this issue, the UCO team—comprised of researchers Sana Boubehziz, Antonio Sánchez Rodríguez and Vidal Barrón from the Edaphology group within the Department of Agronomy (DAUCO)— has explored ways to mitigate the damage caused by high temperatures, which they aim to counteract through the use of organic additives that enhance soil resistance. This contribution adds to a comprehensive, multi-stakeholder strategy embodied in the European Soil Monitoring Directive, which aims to achieve healthy soils across Europe by 2030.
Mediterranean soil, at risk
As the principal investigator on this project, Sana Boubehziz, explains, the soil samples were first labeled with radioactive carbon-14 isotopes to monitor the microorganisms' respiration. The goal was to test the resilience of two types of Mediterranean soil—one calcareous from Córdoba and the other more acidic from Badajoz—under different temperature scenarios ranging from 20 to 50 degrees. While the results showed how high the temperature can rise before the soils lose their functionality, they also highlighted the urgent need to find mitigating solutions to slow the degradation of soils that are exposed to increasingly high temperatures year after year.
These mitigation measures could involve incorporating organic amendments rich in organic matter to boost soil resilience. This has been demonstrated in tests using alperujo, or olive pomace, the primary byproduct of olive oil production, and organic waste from the treatment plants of Córdoba's municipal water and waste management companies. Sana Boubehziz explains that after a two-week incubation period, soil samples that received organic additives showed a significant increase in both resistance and phosphorus availability. Specifically, alperujo proved most effective, increasing soil resistance to 50 degrees, once again highlighting the potential of this byproduct from one of Andalusia's main industries to be part of circular economy strategies.
According to the researcher, beyond its practical applications, the study's main contribution is to highlight the specific challenges and needs of a soil type found in Mediterranean areas that is threatened by the effects of climate change. "Each soil is unique," she explains, "and must be managed in a way tailored to its characteristics." For example, in agriculture, "it's been proven that using organic-based fertilizers is healthier for the soil, making it last longer and produce more, making it more profitable in the medium term." This profitability isn't just about growers' bottom lines; it also has a social dimension. Soil, considered a non-renewable resource due to its slow regeneration, plays a key role in carbon sequestration, which makes it a valuable tool against the very climate change that is accelerating its degradation. Taking good care of soil is a way to break the cycle.
Journal
European Journal of Soil Science
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Soil Preservation in a Warming Climate: Organic Amendments Enhance Microbial Carbon Use Efficiency in Mediterranean Soils
Tiny molecules unlock big gains in soil health
Maximum Academic Press
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Framework of how lignin-derived (LSM) and humus-derived (HSM) small molecule addition promotes the formation of newly formed mineral-associated organic matter (13C-MAOM) from 13C-labeled straw in sodic and non-sodic soils. Blue and light purple arrows represent the effects of LSM and HSM addition on exchangeable sodium percentage (ESP) and microbial communities, respectively. The percentage indicates the degree of effect of biopolymer-derived small molecule addition compared with the control with no LSM and HSM addition, with positive and negative values indicating enhancement and reduction, respectively.
view moreCredit: Pedosphere
Converting crop straw into stable soil organic matter (SOM) is essential for sustainable farming and climate resilience—but it's notoriously inefficient in saline-alkaline soils. A recent study explored whether tiny, naturally derived organic molecules could provide a microbial boost. By adding lignin- and humus-based small molecules (LSMs and HSMs) to straw-amended soils, researchers observed remarkable gains in the formation of stable mineral- and particulate-associated carbon. These changes were driven by shifts in microbial communities and enhanced cross-trophic interactions. In particular, humus-derived compounds significantly reduced soil sodicity and improved microbial processing of straw. The findings offer a promising pathway for regenerating degraded agricultural soils.
Soil organic matter plays a foundational role in agricultural productivity, climate mitigation, and ecosystem balance. Straw return—a widely used strategy to enrich soil organic matter (SOM)—suffers from low conversion efficiency, especially in sodic soils where high sodium levels suppress microbial activity. Attempts to boost this process with microbial inoculants have often failed, as introduced microbes struggle to compete with native communities or survive in harsh soil conditions. Meanwhile, studies suggest that small-molecule organics can shift microbial populations and stimulate decomposition. Due to these limitations and emerging insights, there is a growing need to investigate whether small molecules can catalyze microbial processes and improve SOM formation in stressed environments.
To explore this question, a team of scientists from the Chinese Academy of Sciences and South China University of Technology conducted a 15-week experiment, published (DOI: 10.1016/j.pedsph.2024.05.012) in Pedosphere in June 2025. They introduced biopolymer-derived small molecules—extracted from lignin (LSMs) and humus (HSMs)—into both sodic and non-sodic soils along with ¹³C-labeled straw. The study examined how these amendments influenced microbial community structure, enzymatic activity, and the formation of stable SOM fractions. Their findings revealed that humus-derived small molecules not only reduced soil sodicity but also enhanced microbial pathways responsible for straw degradation and long-term carbon stabilization.
The addition of HSMs and LSMs significantly boosted the conversion of straw into 13C-labeled mineral-associated (MAOM) and particulate organic matter (POM), with HSMs achieving greater efficiency. In sodic soils, HSMs reduced exchangeable sodium percentage by over 11%, easing stress on microbial communities. Microbial diversity increased markedly, with higher richness of bacteria, saprotrophic fungi, and phagotrophic protists. Notably, beneficial taxa such as Bacillus, Chaetomium, and Flabellula were enriched.
Network analysis revealed strengthened cross-trophic interactions—particularly between decomposers and protist predators—following small molecule addition. These interactions played a pivotal role in carbon stabilization, alongside elevated enzymatic activities (β-glucosidase and β-xylosidase) and microbial necromass accumulation. Random forest modeling confirmed cross-trophic interactions as the top predictor of SOM formation. Collectively, the results indicate that biopolymer-derived molecules activate complex microbial pathways that lead to more efficient and stable carbon incorporation in soil.
“Our study demonstrates how strategic use of natural small molecules can reshape the soil microbiome to benefit carbon cycling,” said Dr. Jiabao Zhang, corresponding author of the study. “By stimulating microbial cross-feeding and enzymatic processing, especially under saline stress, we saw a notable increase in stable soil organic matter. These findings could help reimagine how we manage straw residues and rehabilitate degraded soils—using tools already present in nature.”
The research presents a scalable, biologically aligned strategy to improve soil health and carbon retention, especially in saline-affected regions. Adding humus-derived small molecules to straw-return systems could enhance SOM formation, increase microbial biodiversity, and mitigate sodic stress—all without relying on synthetic amendments. As global agriculture faces increasing pressure from soil degradation and climate change, this method offers a promising nature-based solution. Future field studies are needed to validate these lab-scale results across different soil types and cropping systems, and to evaluate the long-term persistence of microbially stabilized carbon in real-world conditions.
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References
DOI
Original Source URL
https://doi.org/10.1016/j.pedsph.2024.05.012
Funding information
This work was financially supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Nos. XDA28110100 and XDA28020202), the National Key Research and Development Program of China (No. 2022YFD1500203), the National Natural Science Foundation of China (No. 42177332), the China Agriculture Research System (Nos. CARS-03 and CARS-52), the Youth Innovation Promotion Association of Chinese Academy of Sciences (No. 2023325), and the Anhui Provincial Key Research and Development Project, China (No. 2023n06020056).
About Pedosphere
Pedosphere is a peer-reviewed international journal established in 1991 and published bimonthly in English by Elsevier and Science Press. It is jointly sponsored by the Soil Science Society of China and the Institute of Soil Science, Chinese Academy of Sciences, in collaboration with five leading Chinese institutions in soil science. Under the editorship of Prof. Shen Ren-Fang, the journal publishes high-quality original research and reviews spanning the full spectrum of soil science, including environmental science, agriculture, ecology, bioscience, and geoscience. Topics of interest include soil physics, chemistry, biology, fertility, plant nutrition, conservation, and global change. All submissions undergo rigorous double-blind peer review by an international editorial board and expert panel. Pedosphere is indexed in major databases such as SCI Expanded, SCOPUS, BIOSIS, CAB Abstracts, and CNKI, making it a widely recognized platform for advancing soil science research globally.
Journal
Pedosphere
Subject of Research
Not applicable
Article Title
Microbiological mechanisms of lignin- and humus-derived small molecule addition promoting straw conversion into soil organic matter in a sodic soil
Article Publication Date
21-May-2026
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