Envy for food ensures order in the forest: The complex steps in the process of leaf decomposition are taken over by millions of different microbes on the forest floor. Recent studies have now shown that the distribution of tasks among these decomposers takes place through strong competition for the best and fastest adaptation to the decomposition functions – and this is not always peaceful.
Microorganisms are crucial factors in the forest ecosystem: they cannot be seen with the naked eye, as they colonize the forest floor by the millions and decompose fallen leaves, dead plants and dead wood. In this way, they bring important organic components such as carbon back into the forest cycle and preserve the quality of the forest soil. But how do the microbes divide up the various tasks involved in breaking down foliage? Do the different microbial communities work together or do they compete with each other?
A mixture of molecules brings light into darkness
Simon Schroeter from the Max Planck Institute for Biogeochemistry in Jena and his colleagues have now taken a closer look at the interaction of the decomposer communities during decomposition. To do this, they analyzed samples of dissolved organic matter – a complex mixture of the molecules of the foliage layer and natural substances from the environment. Since this material also contains components of the microorganisms, the chemical analysis also provides information about the active microbial metabolism in the material – and thus about the role of the microbes in decomposing leaves.
The researchers examined more than 6000 molecules that were found in dissolved organic substances in the leaf litter of beech, oak, pine and grass litter. They took the samples from two different locations in Thuringia and Brandenburg. “Although the exact structure of the individual molecules was still largely unknown to us, we were able to group them according to their possible origin using a network analysis,” reports Schroeter. The groups of molecules found in this way could then be assigned to the various metabolic pathways using microbiological databases.
Elbow tactics on the forest floor
The results reveal an astonishing connection: Apparently, the distribution of tasks does not depend on who is better able to take on which function. This is because the microbial communities, be they fungi or bacteria, all have similar requirements for decomposition and are able to perform the same functions. It is much more about who can adapt best and fastest to the overall situation and who is assertive.
“It seems to be much more important how much of the respective function can be fulfilled locally at any given time and how well the respective actors within the decomposition community are able to fulfill this task,” explain Schroeter and his colleagues. For example, once the first step in the decomposition of a dead leaf, the softening of the leaf surface, has been completed, the next step is to penetrate the leaf tissue and start further decomposition processes there. The researchers’ analyzes showed that the microbes can adapt to these different tasks within a few days.
However, when competing for the fastest adaptation to the new decomposition processes – and thus for the largest food supply – things are not always peaceful, as analyzes of the intermediate and end products of the microbial metabolism reveal. Accordingly, the microorganisms produce inhibiting and even deadly antibiotics with which they specifically weaken or eliminate their competitors. This gives them a strong competitive advantage in the competition for food supply.
Competition spurs on
The mutual elimination of decomposers does not sound very advantageous for the forest ecosystem at first glance. But Schroeter and his colleagues see this competition as a means of advancing and optimizing the adaptation of the microbial community. So the argument over food could be constructive and support those species whose skills are very well adapted to the food supply – and thus favor the species that are best for the forest floor and the ecosystem.
Source: Max Planck Institute for Biogeochemistry; Specialist article: Nature Portfolio, doi: 10.1038/s41598-022-11485-1