How Land Use Shapes Vital Soil Fungi in Calcareous Soils
In the thin, challenging soils of rocky landscapes, an ancient partnership between plants and fungi holds ecosystems together—and human activity is changing this hidden world in ways we're just beginning to understand.
Beneath every step we take on calcareous soils—the chalky, alkaline earth that covers nearly a third of the world's ice-free land—exists a biological internet that has operated for over 400 million years. This hidden network connects plants, transfers nutrients, and sustains entire ecosystems, all through microscopic filaments of arbuscular mycorrhizal (AM) fungi. These ancient organisms form partnerships with most land plants, from towering trees to humble crops, in one of Earth's most successful and widespread symbiotic relationships.
Today, this unseen world is at a crossroads. As humans transform landscapes through agriculture and other activities, we're inadvertently reshaping these fungal communities—with profound consequences for soil health, crop productivity, and ecosystem resilience. Nowhere is this relationship more critical than in calcareous soils, where nutrients are often locked away in forms that plants struggle to access alone. The story of how land use changes these microscopic inhabitants reveals not just the vulnerability of soil ecosystems, but also potential solutions for more sustainable coexistence with the underground world that feeds us.
Arbuscular mycorrhizal fungi belong to the phylum Glomeromycota and have formed mutualistic relationships with plants for hundreds of millions of years. These remarkable organisms create intricate structures within plant root cells called arbuscules, where the exchange of nutrients occurs. The fungi extend far beyond the root zone with microscopic filaments called hyphae, creating a vast network that acts as an extension of the plant's root system.
This partnership is a classic example of nature's barter system: plants supply the fungi with carbon-rich sugars produced through photosynthesis, while the fungi provide their host plants with essential nutrients like phosphorus, nitrogen, and micronutrients that would otherwise be inaccessible. This exchange is particularly vital in calcareous soils, where high pH levels often render phosphorus and other key nutrients insoluble and difficult for plants to absorb.
When conditions become unfavorable—due to drought, temperature extremes, or disturbance—AM fungi produce spores as survival structures. These microscopic repositories contain everything needed to regenerate the fungal network when conditions improve. The abundance and diversity of these spores in soil serves as a crucial indicator of the health and resilience of the mycorrhizal community.
Different AM fungal species produce distinct types of spores that vary in size, shape, and color. Some species, like those in the genus Funneliformis mosseae, produce larger, darker spores, while others like Rhizophagus intraradices create smaller, lighter-colored spores. This diversity matters because different fungal species offer varying benefits to their plant partners, creating a complex underground economy where variety translates to ecosystem stability.
Years of plant-fungal partnership
Of land plants form mycorrhizal associations
Of world's ice-free land is calcareous soil
Conversion of natural ecosystems to agricultural land represents one of the most significant transformations affecting AM fungal communities. Research has consistently demonstrated that agricultural soils typically host less diverse AM fungal communities compared to natural ecosystems 3 . The reasons for this decline are multifaceted:
The impact extends beyond mere numbers. Intensive management tends to favor AM fungal species that are fast-colonizing generalists, while specialist species that may offer unique benefits to specific plants often decline 8 . This represents a potential loss of functional diversity that could compromise ecosystem resilience.
In contrast to agricultural systems, natural areas typically maintain richer, more diverse AM fungal communities. These ecosystems provide a mosaic of different plant species with varying root architectures and chemical signatures, creating more niches for diverse fungal species to occupy. The absence of soil disturbance allows established hyphal networks to persist and develop over time, creating a stable underground infrastructure.
Non-agricultural soils also tend to have more consistent levels of glomalin, a sticky glycoprotein produced by AM fungi that acts like "soil glue" to bind particles together into stable aggregates 5 . This protein not only improves soil structure but also represents a significant carbon reservoir, linking fungal activity to carbon sequestration—a crucial consideration in our era of climate change.
To understand how land use affects AM fungi in calcareous soils specifically, a comprehensive study examined fungal communities across multiple locations in Central Europe, including calcareous soils in the upper Rhine valley 3 . This research provides some of the clearest evidence of how human activity reshapes these vital underground communities.
Sixteen sites were selected representing different soil types (including calcareous Regosols and Leptosols) and land use intensities (from grasslands to intensively managed arable lands)
Field soil samples were collected at the beginning of the vegetative period in spring
To propagate and observe the AMF communities, "trap cultures" were established using specific host plants and maintained under controlled conditions for two complete vegetation periods
Researchers identified AM fungal species through careful examination of spore morphology, color, size, and wall structure under microscopy
This method allowed scientists to create a comprehensive census of the AM fungal species present in each soil type under different management regimes, providing a clear picture of how land use shapes these communities.
The findings from this extensive survey revealed striking patterns about where different AM fungi thrive—and how human activity has rearranged these underground communities.
| Soil Type | Land Use | Total Species | Unique Species |
|---|---|---|---|
| Calcareous Regosols | Grassland | 28 | 8 |
| Calcareous Regosols | Arable | 19 | 2 |
| Siliceous Cambisols | Grassland | 25 | 7 |
| Siliceous Cambisols | Arable | 17 | 1 |
| Calcareous Leptosols | Natural | 32 | 11 |
The data reveals a consistent pattern: regardless of soil type, arable (cultivated) lands hosted significantly fewer AM fungal species compared to grasslands or natural areas. Calcareous soils in their natural state supported particularly diverse communities, but this diversity dramatically declined under agricultural management.
This shift from diverse to simplified communities matters not just for ecological record-keeping, but for practical functioning. Different AM fungal species provide varying benefits to plants—some are particularly efficient at phosphorus uptake in alkaline conditions, while others excel at water transport or pathogen protection.
In calcareous soils, where phosphorus availability is naturally limited, the loss of fungal diversity could mean losing precisely those species that are most effective at making this vital nutrient available to crops. A 2024 study on vetch plants in calcareous soils demonstrated that specific AM fungal inoculations could significantly improve plant growth and nutrient uptake, highlighting the very real agronomic consequences of these community changes 2 .
Understanding these microscopic relationships requires specialized methods and tools. Researchers employ a diverse toolkit to uncover the secrets of AM fungal communities and their responses to land use change.
| Research Tool | Primary Function | Application in Calcareous Soils |
|---|---|---|
| Wet Sieving Method | Separates spores from soil particles | Enables spore counting and identification; challenging in calcareous soils due to similar particle densities |
| Trap Cultures | Propagates AM fungi for identification | Uses host plants to maintain and multiply fungal communities from field samples |
| Microscopy Techniques | Identifies spores and root colonization | Requires expertise to distinguish diverse spore types in calcareous soils |
| Molecular Methods | DNA-based community analysis | Provides detailed species composition data beyond spore morphology |
| Glomalin Measurement | Quantifies glomalin-related soil proteins | Assesses fungal contribution to soil structure and carbon storage |
| Most Probable Number (MPN) | Estimates infective propagules | Measures functional potential of AM fungal communities |
Each method offers unique insights. Traditional microscopy-based approaches allow researchers to identify spores based on physical characteristics, while modern molecular techniques can reveal species that might not sporate frequently but still play important ecological roles. The combination of these methods provides a more complete picture of these hidden communities.
Recent technological advances have dramatically improved our ability to study these organisms. AMF-specific primers for DNA amplification allow researchers to identify species that might be missed by traditional methods, revealing an even more complex picture of how land use affects these communities 8 . These tools have confirmed that what we see through spores alone represents only part of the story—many functionally important species may be present in root systems but produce few spores, making their detection dependent on these molecular methods.
Understanding the relationship between land use and AM fungal communities isn't just an academic exercise—it has practical implications for creating more sustainable agricultural systems. Research has demonstrated that specific management practices can help preserve or even enhance these vital fungal networks:
The potential benefits extend beyond crop production. Healthy AM fungal communities contribute to soil carbon sequestration through the production of glomalin, a stable glycoprotein that can persist in soils for decades 5 . This connects the management of these microscopic fungi to broader efforts to mitigate climate change through agricultural practices.
Despite significant advances, many questions remain about how best to manage these fungal partners in calcareous soils. Current research is exploring:
Developing AM fungal blends specifically adapted to calcareous soils and particular crops
Determining how to configure agricultural and natural areas to maintain diverse fungal reservoirs
Understanding how these fungi might help crops withstand drought and other climate-related stresses
A 2025 global study on forest systems revealed that the type of mycorrhizal association (arbuscular versus ectomycorrhizal) significantly influences tree species diversity patterns worldwide . This research highlights how belowground fungal partnerships shape the plant communities we see aboveground—a powerful reminder that managing the visible world requires understanding the invisible one.
The intricate relationship between land use and arbuscular mycorrhizal fungi in calcareous soils represents more than just a specialized ecological interaction—it demonstrates the profound, often unnoticed ways human activity alters the natural world. These microscopic fungi, invisible to the naked eye, perform functions that ultimately support the productivity of both natural ecosystems and agricultural landscapes.
As we move toward a future that demands more sustainable approaches to land management, understanding and working with these hidden partners becomes increasingly crucial. The spore abundance in a handful of calcareous soil tells a story of past management, present health, and future potential. By learning to read this story and adjust our practices accordingly, we take an important step toward aligning our agricultural systems with the ecological relationships that have sustained terrestrial life for millions of years.
The challenge—and opportunity—lies in developing land use practices that recognize the quiet but essential work happening beneath our feet, in the hidden world of spores and hyphae that quietly sustains the visible world we inhabit.