Soil MIcrobial responses to land use and climatic changes in the Light of Evolution

Informations projet

SMILE

N° de convention de subvention: 101001608

DOI

10.3030/101001608

Projet clôturé

Date de signature de la CE 17 Decembre 2020

Date de début 1 Mai 2021

Date de fin 30 Avril 2026

Financé au titre de

• EXCELLENT SCIENCE - European Research Council (ERC)

Coût total

€ 1 688 250,00

Contribution de l’UE

€ 1 688 250,00

Coordonné par

STOCKHOLMS UNIVERSITET
Sweden

Periodic Reporting for period 3 - SMILE (Soil MIcrobial responses to land use and climatic changes in the Light of Evolution)

Période du rapport: 2024-05-01 au 2025-10-31

Résumé du contexte et des objectifs généraux du projet

Soil microorganisms are responsible for a large fraction of greenhouse gas emissions from terrestrial ecosystems and produce most of the nutrients needed by plants to grow. They perform these important functions by decomposing organic matter, which is not easy for them to access in soil and is often not nutritionally balanced. In this project, we study soil microorganisms and the strategies they adopt to access soil resources. We hypothesize that soil microbes are such effective drivers of carbon and nutrient cycles because they have evolved to face the challenges of life in soil. In other words, they behave in the best possible way to guarantee their survival and reproduction.

We are incorporating this ecological concept into mathematical models of carbon and nutrient cycling, which now do not keep into account microbial adaptations to environmental conditions and thus cannot reliably predict how much soil organic carbon and nutrients vary due to land use or climatic changes. The newly developed models will improve the way we describe soil processes, thereby making predictions of soil responses more accurate. With this approach, we are answering the long-standing question—how are land use and climatic changes affecting soil fertility and the amount of carbon we can store in soil?

Our main objectives to answer this question are: i) determine how microorganisms adapt to varying resource and water availability in the soil and construct a new theory of microbial adaptation, ii) collect data from the scientific literature on microbial responses to soil amendments and variations in soil moisture, and create a new database with this data, iii) test the mathematical models of adaptation using the new databases and select the models that work best, and iv) assess impacts of land use and climatic changes on carbon and nutrient storage and fluxes using improved soil models that account for microbial adaptation based on the theory developed in objective i).

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

We have developed new models of microbial adaptation focusing mostly on resource acquisition. Microorganisms need to acquire resources to grow, but by doing so they deplete their own source of substrate. Moreover, resource acquisition is costly for the microorganisms because they have to synthesize extra-cellular enzymes and maintain them. As a result, the amount of enzyme produced and the timing of enzyme production need to be tuned so that microorganisms get as much substrate as possible while avoiding unnecessary costs. Besides enzyme production, microbes can also recycle nutrients if they feed on nutrient poor substrates, such as some plant residues. We have developed mathematical models to describe microbial resource acquisition and how they tune both enzyme production and nutrient recycling in a way to provides them the highest benefit, ensuring sustained growth. While developing these new models, we have collected literature data on microbial growth and respiration after drying and rewetting, and found that fungal growth recovers faster than bacterial growth, and that in general recovery is slower in more acidic soil and after a longer dry period. This new data also uncovered a general recovery pattern—after it rains on a dry soil, microbes first face stressful conditions and thus focus on resisting stress, but then they shift their behavior towards resource acquisition and growth. A new dataset of soil carbon and nitrogen in fractions with different levels of accessibility to microorganisms has also been developed, and a new diagnostic model is used to interpret this data. We have also classified eco-evolutionary models of soil processes according to the way they conceptualize microbial processes, and used that to promote an agenda for developing soil and ecosystem models where microbial adaptations as well as ecological processes are taken into account.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

Our new models accounting for microbial adaptation can predict decomposition—the first step in soil carbon and nutrient cycles—as well as traditional models, but using fewer parameters. This means that they are more robust. These models are also helping to understand why certain compounds in plant residues are decomposed sooner than others, and when and why microorganisms alter their carbon-use efficiency—the fraction of carbon consumed that microorganisms convert in new biomass. This efficiency is crucial for understanding carbon stabilization in soil. In fact, through collaborative work, we found that microbial carbon-use efficiency is the most important parameter to determine global soil carbon stocks. As an alternative to changing carbon-use efficiency, we also discovered that microbes can recycle or store intra-cellularly nutrients when they feed on nutrient poor substrates. Nutrient recycling appears an ecologically advantageous strategy in litter decomposition, and nutrient (especially phosphorus) storage is key in ancient, nutrient-depleted soils. These findings could revolutionize the way we conceptualize microbial processes in soils, and points to gaps in our mathematical models that we have just started to fill.

We expect to continue collating literature data on microbial processes—also in response to temperature variations, which we have not explored so far in the project, in parallel to model development and testing. Through collaborations, we are exploring both how spatially heterogeneous environments and complex microbial communities shape decomposition patterns, and how to implement our mathematical models of adaptation in operational soil and ecosystem models. Two new databases (responses to rewetting; dynamics of carbon and nitrogen in soil fractions) are published, and a third one on temperature responses is in development.

Schematic of project rationale