A Dutch meta-analysis of 126 studies conducted worldwide illustrates the consequences of nitrogen accumulation for soil microfauna. Effects vary across species. Climate factor
by Matteo Cavallito
A higher nitrogen presence is known to affect soil and plant status with potentially negative effects. “But much less is known about the effects of nitrogen on the animals that live in or on this soil,” explains Juan Gallego-Zamorano, a researcher at the Radboud Institute for Biological and Environmental Sciences in Nijmegen, the Netherlands, and co-author of a recent study on the element’s impact on invertebrates and insects.
The investigation is based on a meta-analysis of 126 studies conducted worldwide and tries to paint a picture of the consequences of the element’s accumulation, mainly from fertilizers and animal manure. The results are variable: in areas with high nitrogen inputs, nematode diversity, for example, decreases. At the same time, other species benefit from the additional supply of the nutrient. A complex situation, in short.
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Variable effects from nitrogen
Looking at previous research, the authors calculated the number of species and specimens of nematodes and arthropods, such as butterflies, grasshoppers or spiders, found in the experimental plots to which nitrogen had been added. The presence of some arthropods, such as butterflies, is reduced. But the rule does not apply to all species.
Unlike butterflies, “Arthropods that do not metamorphose completely, such as spiders or locusts appear to do well with more nitrogen and are increasing in numbers,” explains co-author Aafke Schipper.
Microfauna, in other words, also seem to highlight the complex nature of the overall balance between the ecosystem and nitrogen. This element represents an essential nutrient for plants but also a sometimes negative factor for water quality capable in some cases of causing eutrophication (the excessive enrichment of nutrients) generating health risks for animals and humans.
Climate and crops
Researchers also pointed out how the impact of nitrogen changes depending on climate. Higher temperatures amplify the negative effects of high nitrogen levels on insects that suffer the greatest accumulation. More frequent and intense rainfall, on the other hand, mitigates the impact of the element on nematodes through leaching (the separation of the element itself) from the soil exerted by water.
“These results show that climate change may amplify the negative effects of nitrogen due to higher temperatures and drought,” the researchers explain.
The processes examined also affect crops. Insects subject to the negative effects of nitrogen, for example, include pollinators that play a crucial role in the survival of some crops. At the same time, the increased presence of some arthropods – such as locusts – presents a threat to agricultural yields.
Counteracting emissions to protect ecosystems
The study results provide access to a broader understanding of often underestimated mechanisms by highlighting the need to ensure a balance in the application of the element. “In the last decade, there have been many studies reporting invertebrate declines in various locations and world regions,” the research states. “The anthropogenic enrichment of N may contribute to the decline of insects. This in turn may affect important ecosystem services such as pollination, pest control, or nutrient cycling.”
In addition, “The impacts of N on invertebrate communities might be amplified by climate change, which is in accordance with findings reported in other literature.” Therefore, the researchers conclude, “Counteracting or mitigating measures of both N emissions and global warming is needed to maintain invertebrate community integrity and ecosystem functioning.”