Climate determines the distribution of fungal traits at the continental scale

Fungi are predominant components of terrestrial ecosystems in terms of biomass and diversity. They are the dominant decomposers of organic plant material, directly influencing global carbon and nutrient dynamics, soil fertility, and thereby acting as primary agents for climate change. Given that different fungi process organic matter at vastly different rates, their composition in an area can provide a tangible link between biological communities and the functioning of ecosystems. Yet, incorporating information about fungal communities into biogeochemical models requires an understanding of how different types of fungi function in different parts of the world and their broad-scale distribution – knowledge that lags far behind the understanding of floral, faunal and bacterial biogeography.

In a new study published in Nature Microbiology, a collaborative team of researchers including Daniel Maynard from the University of Chicago, who will join the Crowther Lab at ETH in April as a Postdoc, and Thomas Crowther, Professor for Global Ecosystem Ecology at ETH Zurich, have explored the linkages among functional trait expression – the characteristics of fungi -, phylogeny and climate across broad spatial scales.

The dominance-tolerance trade-off

There are tens of thousands of species of decomposer fungi across the world, all fulfilling a crucial role in the carbon cycle. However, due to the amount of different species, it is impossible to precisely identify which species live in which environment. It is, however, possible and crucial to understand and measure their traits that tell us what specific function in the decomposition process is fulfilled under which conditions.

For their research, the team around Maynard and Crowther used a standardized trait-based approach to quantify the niches of 23 species of wood decay fungi, collected from Alaska to Puerto Rico. Focusing on these functionally equivalent fungi from across a broad geographic range allowed the researchers to focus on the expression of a wide range of ecological performance traits that relate directly to the ability of an organism to survive in a given environment.

The results show the partial linkage between fungal trait and climate. Despite being collected from vastly differing areas and climate conditions, all fungi shared similar preferences for warm and moist conditions. Yet, what differed substantially across the fungi was their ability to survive stressful environmental conditions and their ability to overgrow and displace their neighbours. Specifically, slow-growing, stress-tolerant fungi exhibit weaker combative abilities than fast-growing fungi, which conversely are able to survive under a smaller range or environmental conditions. In short: fungi expressing traits associated with high thermal and moisture stress tolerance are distinct from fungi expressing high competitive ability and rapid space acquisition.

Carbon decomposition and biogeographical patterns

The fungi exhibited a clear dominance-tolerance trade-off between competitive ability and stress tolerance, which is partially linked to the environmental conditions under which the fungi were collected. The results show that highly competitive, fast-growing fungi live in the tropics and are able to decompose carbon fast. Slow-growing fungi live in cold, dry, or stressful environments and decompose carbon slowly.

Although the exact drivers of this relationship between trait expression and climate remain to be elucidated, in their analysis, Maynard and Crowther were able to show that these traits have consistent global distributions, which allows them to predict what types of fungi exist in a given environment and how these fungi function in those environments. These results enhance our ecological understanding of these functionally important organisms and are the crucial first step to generating predictable biogeography patterns able to deliver information on climate change.