VUB research: soils also have a memory ​

In his PhD research, VUB researcher Elias Goossens investigated how plants influence the soil in which they grow, and how that altered soil subsequently determines the growth of other plants. Plants not only extract nutrients from the soil, they also alter it. Through their roots, they influence the chemical composition of the soil, its structure and the community of bacteria, fungi and other micro-organisms living there. These changes then have an effect on the plants that grow in the same spot later on and, as it were, form the soil’s memory.

In this context, scientists refer to ‘plant-soil feedback’: a continuous interaction between plants and their environment. “You can think of the soil as a memory of the plants that grew there before,” says Goossens. “Plants leave their mark, and this helps determine which species can thrive there afterwards.”

In the past, this plant-soil feedback was usually studied in laboratory experiments involving just one plant species at a time. Such monocultures are rarely found in nature. Grasslands consist of dozens of species that are constantly competing and cooperating with one another. Goossens therefore investigated what happens in real plant communities. The results show that experiments involving a single species do not provide a reliable prediction of what happens in natural grasslands. The interactions between different species are far more important than previously thought.

It is striking that dominant plant species in species-rich grasslands are often held back by their own impact on the soil. They create conditions that hinder their own further growth because they promote pathogens in the soil, which mainly affect plants of the same species. Rarer species therefore benefit from this and are given more opportunities, as those dominant species fare less well. This mechanism helps prevent a single species from crowding out all the others. “This negative feedback acts as a natural brake on dominant species,” says Goossens. “As a result, many different plant species can continue to coexist.”

The research also sheds new light on invasive plants – non-native species that spread rapidly and can disrupt local ecosystems. A popular theory suggests that these plants are successful because they escape the pathogens and soil organisms that hold them back in their native habitat. Scientists refer to this as the ‘Enemy Release Hypothesis’.

However, the results paint a more nuanced picture. In species-rich grasslands, invasive plants do not automatically have an advantage. Only when biodiversity declines and fewer different species are present can invasive plants benefit more strongly from the absence of their natural enemies. This makes species-poor ecosystems more vulnerable to invasions, which is consistent with observations in nature. Furthermore, another mechanism is at play: with more native species in a vegetation community, more ecological niches are filled, making it more difficult for an alien species to occupy such a niche – as fewer are available – and thus to establish itself and become invasive. “We worked with both sterilised and non-sterilised soils, which enabled us to determine the importance of these two mechanisms separately,” said the researcher.

Goossens also investigated the role of nutrients in the soil. He found that it is not only the quantity of nutrients, but also the ratio between, for example, nitrogen and other elements, that determines how strongly plant-soil feedbacks operate. This is important because human activities are increasingly disrupting that balance. Fertilisation, nitrogen pollution and invasive plant species can alter soil chemistry. For example, the invasive giant goldenrod (Solidago gigantea) is known to increase the availability of nitrogen in the soil by accelerating the decomposition of organic matter.

According to Goossens, these changes can undermine the natural mechanisms that maintain biodiversity. “When plant species disappear, we don’t just lose species above ground,” he says. “The complex interactions in the soil are also disrupted. As a result, a few dominant species can gain the upper hand, making it easier for invasive plants to establish themselves.”

The study shows that biodiversity is more than just a collection of species. A species-rich grassland also harbours a hidden network of interactions between plants, soil organisms and nutrients. It is precisely this underground interplay that ensures ecosystems remain stable. When diversity declines, a self-reinforcing chain reaction can occur, opening the door to further deterioration of nature.

With his PhD, Elias Goossens provides new insights into the hidden processes that determine how grasslands function and why biodiversity is essential for healthy and resilient ecosystems.

PhD title: Impact of plant-soil feedbacks on invasive plants and co-existence in grassland communities

Further information:

Elias Goossens: elias.goossens@vub.be

Supervisor: Professor Harry Olde Venterink

Publications:

Frans Steenhoudt

Perscontact wetenschap en onderzoek

• frans.steenhoudt@vub.be
• +32 4 75 68 64 69

• www.vub.be