About ten years ago in my lab, we started working on a set of soil saprobic (decomposer) fungi. These fungi all came from the same grassland soil, east of Berlin. Our idea was to understand better how fungi ‘tick’, by using a trait-based approach. This basically means dissolving species into a combination of measurable characteristics, and then, by comparing these across the set of about 30 fungi, to learn about fundamental trade-offs in fungal biology and ecology.
One of the questions that we had in the beginning was: is there a fungal economics spectrum? This question has been inspired from seminal work in plant ecology, and a spectrum is basically an axis along which different species can be arrayed, explaining a wide range of variability that exists among different organisms. The famous leaf economics spectrum is an example for plants, exemplifying how leaves can be constructed in fundamentally different ways: fast and cheap, or expensive and durable, for example. Other exercises include the root economics spectrum, which turns out to rather be more like a space, because there are two major axes that describe what roots can do (this is a paper by Dr. Joana Bergmann, a former PhD student and postdoc in our lab).
Now, 10 years after we started with the set of fungi in our lab, we propose what the fungal economics spectrum looks like, in a paper led by Dr. Tessa Camenzind, a current postdoc in our lab in Berlin. Tessa had the vision to take all the data that we had collected and put it together.
What Tessa found is this: there is not really a fungal economics spectrum (a single axis), or a space (two axes), but there are actually three axes that describe how fungi operate.
The first axis captures the dense-fast continuum of fungal growth, and this is quite similar to what has been found also in other organisms. It basically means, if you’re a fungus you can spread fast across your habitat, or you can grow with rather densely packed mycelium that doesn’t advance very quickly. Or of course everything in between, these are the endpoints that determine this axis. You can also think of this as exploitative or exploratory, or slow and fast growth.
The first axis certainly did not come as a surprise at all, as also others have found that this fundamental trade-off describes much in fungal ecology. By contrast, axis number 2 is substantially less obvious: mycelium flexibility. This axis reflected the ability of a mycelium to recycle internal resources, and captured also stoichiometric flexibility, meaning flexibility in terms of elemental composition of the mycelium.
The third axis captured carbon acquisition traits, such as enzymatic capabilities and the ability to use more complex sources of C. The interesting thing is that the three axes were orthogonal, that means independent. So the trade-offs were not among these axes, but along each one of them.
These three axes combined explained much of the trait combinations that exist in our set of fungi. What’s immediately apparent ist that the species are basically spread pretty equally across this 3-D space, there aren’t really any preferred ‘corners’. Also, each of these axes relate to certain soil functions, for which we also had data. The way that these functions in soil correlated with the basic three axes was quite interesting, in that it suggests that certain fungal-driven processes could be quite resistant to some environmental stressors.
We don’t really know if this economics space of fungi is a universal pattern, given that we worked on fungal isolates from just one soil. The latter is not really a limitation per se, but a strength, because it allows us to think about fungi that potentially co-occur in the same soil. This is an advantage over working with fungi without such an ecological context.
Now that this analysis is available, other research groups can test if this holds also more broadly.