Apart from adapting to changing seasons, plants have little need to adapt to variable environmental conditions on their own. The soil stores rainwater and nutrients for them, among other things, and then makes everything available – essentially on demand. The soil even keeps pollutants away from plants. However, geoecologist Hermann Jungkunst and his team, together with researchers from Hamburg, Bonn, Kassel, Berlin, and Hanover, have investigated what happens when the soil can no longer provide such “services” due to overuse (degradation). Specifically, the question is when a tipping point is reached: “Whether one can recognize when it is reached before it is too late.”
The associated research project is called PRODIGY* and was funded by the Federal Ministry of Research, Technology and Space (BMFTR). A tipping point is a sudden change, explains Hermann Jungkunst, providing some background. Like a dam that bursts – which can no longer hold back the water – when the pressure, the stress, is too high or lasts too long – and the system tips over. For the soil, this could mean: “Things go well for a while. Agricultural land can compensate for drought for a long time.” But suddenly and almost irreversibly, it can no longer do so.
The research focused on the tri-border area in the Amazon region – Bolivia, Brazil, and Peru – an area particularly rich in biodiversity and, at the same time, a region threatened by drought. According to Jungkunst, the idea was to understand the effects on ecosystems through three different communities. Together with his team, he investigated chemical-physical questions as part of the interdisciplinary project, he explains his role in the matter. More specifically: The research team he led examined whether soil emits different greenhouse gases depending on whether it is located in an intact rainforest area – or whether it has been used for agriculture for a long time: “In other words, whether a tipping point has been reached due to the agricultural use of the soil.”
The other PRODIGY partners have focused on other aspects, Jungkunst adds. Here, too, the question was what effects occur when a tipping point is reached. Jungkunst: “The background is that changes in the soil ecosystem can have effects on other – related – systems.” He is referring to economic and social systems. In times of rising gold prices, the researchers observed, for example, that gold mining is already significantly more economically lucrative for the local population than agriculture. “Gold mining is one of the most environmentally damaging industries – the consequences for soils and ecosystems are dramatic,” says scientist Jungkunst. Most dramatic is that gold has almost no practical use for people, it just looks good. “But people have always been fascinated by it – we should all do without it.”
But back to his team and their work in the Amazon region: At a total of four sites with different land uses – each at 12 different farms – the researchers dug large holes that were about one meter deep and two to three meters wide. Soil samples were collected. In addition, and in a relatively straightforward manner, the scientists allowed gases escaping from undisturbed soil surfaces to accumulate in airtight containers – and filled them into small bottles. These gas samples were then analyzed in the laboratory in Landau. Hermann Jungkunst: “The gases in the untouched forest were as expected. In the case of the gases from the young and forest-adjacent agricultural areas – but also after about 10 years of use – we observed that the material fluxes were disrupted.” The studies focused on the three main greenhouse gases, which the researchers used as indicators of an intact ecosystem: CO2, N2O (nitrous oxide), and methane.
For example, the researchers confirmed that forests – especially in the soil – are better carbon sinks than farmland. Surprisingly, pastureland stores a similar amount of carbon as forest soil – but methane uptake is lower. “Normally, soils remove methane from the atmosphere and sequester the greenhouse gas in the soil.” In the older pasture soils studied, this capacity was already reduced. And the nitrous oxide measurements suggest that the nitrogen cycle in the cultivated areas is disrupted.
Jungkunst concludes: “The agricultural areas we studied have crossed the tipping point.” Or, to put it more generally: The cultivated areas no longer function as they should. They can no longer provide the services expected of them. The result: They can no longer produce as much.
To understand all this more precisely, one must also address the topic of biodiversity. It concerns fungi, earthworms, and microorganisms that naturally live in the soil: “These tiny organisms perform a wide variety of tasks within the ecosystem,” explains Jungkunst. Some, for example, provide phosphorus to plants. Others break down nitrate or bind heavy metals. Still others loosen the soil so that it can store more water. In short: the diversity of organisms in the soil ensures that the soil can perform its various services at all. And, as Hermann Jungkunst explains, the gas measurements conducted by him and his team indicate that the composition of these microorganisms in the cultivated areas has changed: “Some of the microorganisms are already missing.” Because, to put it simply, if they were all still there, then all the material cycles – as analyzed via gas measurements – would still be intact. In summary, the PRODIGY studies have shown that many organisms with slightly different functional properties can help prevent a tipping point from occurring.
What would be the implication of the studies? Agricultural use of the land in parts of the Amazon is necessary – no question. Hermann Jungkunst agrees, adding: “The untouched rainforest and the agriculturally used areas could be structured in a certain ratio to one another.” The forest could be opened in small sections. In a specific grid structure, for example. This is presumably more beneficial for the biodiversity of the agriculturally used areas – and is also the subject of follow-up studies.
What else is being researched based on PRODIGY? Simone Kilian, a doctoral student in Hermann Jungkunst’s team, aims to identify tipping points long before they are evident. She wants to better understand the associated dynamics to identify early indicators. If, for example, researchers measure lower levels of nitrous oxide in a soil, a tipping point is not far off. Corresponding computer models are intended to map such facts and thus predict under what conditions a specific soil will reach its tipping point and when. But – and this is precisely where Simone Kilian’s research comes in: “There is a fairly large discrepancy between what actually happens in the field and what the existing models predict,” she says.
Hermann Jungkunst is even more explicit on this point: “We were surprised at how poor the existing models are.” What is the problem? The existing models do not sufficiently account for the fact that so-called pseudo-sands are found in Amazonian soil. These stable aggregates of clay and silt particles significantly alter the soil’s water absorption and nutrient balance. Hermann Jungkunst: “So we first have to get a handle on the physics before we can get a handle on the biology.” Simone Kilian wants to properly understand the physics of the soil, the pseudo-sands, and their effects – to make the biogeochemical prediction models significantly more accurate. After all, tipping points should be identified as early as possible – and ideally not reached at all.
*PRODIGY stands for “Production Diversity generates Yield.” Hermann Jungkunst: “Prodigy is a great band from the 1990s. The term means ‘child prodigy.’ Which relates to functional biodiversity.”
Jungkunst HF, Goepel J, Horvath T, Ott S, Brunn M (2022) Global soil organic carbon–climate interactions: Why scales matter. WIREs Climate Change 12: e780. DOI: 10.1002/wcc.780
Kilian Salas, S., Meurer, K. H., Boy, D., Díaz García, E., Woche, S. K., Boy, J., … & Jungkunst, H. F. (2024). The “extra pinch” of pseudosand to enhance tropical biogeochemical processes understanding. Journal of Plant Nutrition and Soil Science, 187(2), 161-170. DOI: 10.1002/jpln.202400090
PRODIGY-Podcast "Digging for Diversity". Elf Episoden tauchen tiefer in die Forschung zu Biodiversität und sozialökologischen Kipppunkten im südwestlichen Amazonasgebiet ein und bieten Einblicke in interdisziplinäre Wissenschaft und Lehre.
