We are investigating ecological systems.
And, basically, ecological systems are comprised of two compartments, the one is above the ground
and the other one is below the ground.
And, in fact, from a human perspective, we predominantly consider the aboveground system because this is what we see.
And we follow up, also, all these interactions above the ground, see the plants growing
and animals consuming what plants produce.
The great majority of what is produced above the ground by plants is not consumed by animals, herbivores we say,
but is actually entering the below ground system as dead organic matter.
In most ecological, terrestrial ecological systems, this is more than 90% of what the plants produce.
So, we are mainly interested in this afterlife effect of plant organic matter, plant litter materials
and look into that from the belowground animal community.
Investigating the relative contribution of above
and belowground residues for belowground systems poses the challenge that we are confronted with soil which is opaque
and which cannot be studied by visual methods.
And one method which allows us to open up that system is using stable isotopes,
labeling of plants with stable isotopes
and then follow up the fate of what plants produce into this below ground system.
And the two isotopes we are heavily using are the isotope of carbon, 13C, and the isotope of nitrogen 15N.
Plants built up their biomass using these compounds, so,
they distribute the carbon throughout the whole plant including leaves and also, of course, roots.
And then we can trace these elements into all belowground animal life or also microbial life and try to understand,
the relative importance of belowground and aboveground compartments of plants in fuelling these belowground systems.
So, the textbook
and public knowledge on the fate of organic matter in terrestrial systems is that it's litter material which falls to
the ground and this is the major food for all the belowground organisms.
But, in fact, this ignores the perspective of all the belowground production of plants.
We labeled actually a beech forest, a mature beech forest, and we followed that carbon into the belowground system.
We found that, actually, the great, great majority of the carbon enters this belowground system via roots.
So, we are confronted with a kind of misperspective at the moment, that,
we assume that it's mainly the aboveground residues which nourish these belowground communities but, in fact,
it looks as if it's the opposite.
It's the belowground system which is of much greater importance for the belowground community.
At least, this is true for a beech forest and the question then, of course, is is this a general phenomenon
or is it only limited to a certain type of forest?
So, we also looked into that, for example,
in arable fields where we actually used maize as a naturally labeled plant
and we actually found a pretty much matching result.
So, we have an important function of the belowground system in providing services to the plants
and thereby providing also services, from the human perspective, in plant productivity,
ensuring sustainable management of arable but also forest systems.
But, there is a second pathway these belowground communities also are important for
and this is by serving as prey for aboveground predators.
Soil animals, in fact, comprise the great majority of all animal life from a biomass perspective.
So, most of the biomass which is produced, animal biomass, is actually below the ground
and this biomass of animals might be used as prey for aboveground organisms.
This is most obvious in birds, presumably, from a human perspective, seeing thrushes
and starlings feeding on the ground and, for example, feeding on earthworms but also insect larvae and so on
but there's a whole wealth of invertebrate predators which also use these belowground animal prey.
These bird predators and invertebrate predators, then also actually feed on aboveground herbivores,
pest species in arable systems for example, and help in keeping these pest species at low levels.
And, in fact, this has been shown now that, via this pathway,
belowground communities also play a major role for the health, basically, of aboveground plant systems and, thereby,
this kind of provides a more holistic perspective on the functioning of terrestrial ecosystems.
We now understand these belowground systems
in a much better way, in the way they function, in the way they are nourished
and this allows us to develop management strategies to foster these systems for improving their functions
and services they provide. I envisage two different perspectives here.
The one perspective is from an arable agricultural systems and plant productivity perspective,
that we can foster the functioning of these belowground systems by coming up with management strategies, improving,
for example, internal nutrient cycling, allowing to reduce input of mineral fertilizers and, on the other hand,
also allowing to reduce the use of pesticides, insect insecticides, for keeping down herbivore
and pest species above the ground. The second perspective is more a conservation biodiversity perspective.
The belowground systems, as we now know, play a major role in nourishing aboveground vertebrates such as birds
but also invertebrates such as insects and, in both of them, we currently see massive decline in diversity
and biomass in Germany but also across Europe and probably across the whole world.
By fostering these belowground systems and providing food for the aboveground world,
they may contribute substantially to mitigating these declines.
So, the challenge we're facing now is that we have to extend our scale from the experimental
and local findings to large landscape
or countrywide scales to implement management strategies fostering these belowground communities for achieving all
these goals.
