NatureToday | Food web disruption due to high nitrogen deposition

Increased nitrogen deposition is a major problem for nature in the Netherlands. The amount of nitrogen in plants almost always does not increase, because nitrogen deposition also has an acidifying effect, the availability of other nutrients to plants decreases. This can lead to a change in the balance of nutrients in the plant.

Too much is not always good

Until now it was assumed that an increase in nitrogen deposition leads to an improvement in the food quality of plants. Animal tissues are much more rich in nitrogen than plant tissues, so it is hypothesized that nitrogen availability is the limiting factor for animal growth. However, this turns out to be only partially true. As nitrogen deposition increases, other important nutrients (nutrients) can decrease significantly compared to nitrogen, causing deficiencies of other nutrients and actually reducing plant quality. Not all plant-eating species are equally sensitive to this. Specialists are optimally adapted to the specific food quality of a single plant species. They are therefore more sensitive to changes in food quality, and moreover, they cannot metamorphose into other host plants. Generalists actually adapt to deal with variation in food quality and can improve their nutritional intake by eating different plant species.

Effects in the food chain

A change in the availability of nutrients often has consequences for the production of amino acids, fatty acids, and vitamins. Because many of these substances are essential—animals cannot produce them themselves and therefore must absorb them from plant tissues—and these substances are only partially passed down every step in the food chain, it is their decrease in plants that first causes problems at the top of the food chain. . In the case of the sparrowhawk, for example, this leads to a lack of vitamins, which leads to deformities in the fetuses.
In addition to the lack of essential nutrients, plants can also make a difference in antidepressants and toxins. As the increase in nitrogen deposition reduces carbon-containing antitrophic substances, insect pests will occur initially. On the other hand, an excess of nitrogen leads to an increase in nitrogen toxins. The incidence of insect pests and the decrease in insect damage are likely due to differences in the production of these substances in the plant. Effects vary, among other things, because not all plant species produce nitrogen-containing toxins, because trees grow less quickly in highly acidic soils, and carbon-containing anti-pollutants may be more concentrated.

Translation for politics and administration

Although in many cases elevated nitrogen deposition alters the food quality of plants, the strength and direction of the effect on animal species is not easy to predict. This effect is determined by the extent and duration of increased nitrogen deposition, the natural buffering and nutrient richness of the soil, specific quality aspects that change for each plant species and the survival strategy of the animal species itself. Knowledge about these aspects makes it possible to predict whether a species will benefit or suffer, and how strong that effect will be. It appears that generalist species are more likely to benefit and that specialized species with optimal nitrogen are less likely to be affected. This process alone eventually leads to a decrease in the biodiversity of animals.

This loss has already occurred in desert land regions, but similar processes can also be seen in forests in sandy soils, quicksands and coastal dunes. At present, we still know too little about the effects on plant food quality to determine whether the current critical sedimentation values ​​for Natura2000 habitat species need to be further tightened. What we do know is that restoring vegetation structure and composition on chemically disturbed soils does not necessarily improve food quality. Measures against nitrogen deposition can also inadvertently contribute to further turbulence. For example, the acid cutting of the soil of desert lands removes not only nitrogen, but also many other important elements, which can further deteriorate the food quality of plants.

conclusion

Nitrogen deposition leads to many changes in the plant. An increase in plant nitrogen is often accompanied by a decrease in other elements and nutrients. How animal species respond to this depends on the species’ survival strategy. Therefore, deepening knowledge in these areas is crucial to better understand the impact of nitrogen deposition on animals. Only then can targeted remedial measures be developed to solve this problem.

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Text: Kevin Gorts, Joost Fogels and Maren Nijsen, Bargerveen Foundation
Images: Marijn Nijssen, Bargerveen Foundation (Main image: Nachtpauwoog)

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