Noémie A. Pichon, Seraina L. Cappelli, Santiago Soliveres, Norbert Hölzel, Valentin H. Klaus, Till Kleinebecker, Eric Allan

Nitrogen is an important nutrient for plant growth and its use in agriculture has increased dramatically, resulting in large amounts of nitrogen being introduced to ecosystems. High levels of nitrogen can cause changes in the plant community above ground (it typically reduces diversity and changes the type of plants present) and in the physical and biological properties in the soil. This can directly and indirectly influence processes occurring in the ecosystems. An important process is the decomposition of plant litter. It is important for recycling dead plant material and making the nutrients stored in the dead material available again. We know relatively little about how nitrogen influences decomposition through these different above- and belowground pathways and how important the different pathways are.

In order to find out, we set up an experiment in which we independently manipulated nitrogen enrichment, plant diversity and the type of plants present (based on their growth rates because fast growing plants do better at high nitrogen). We tested how well the soils under the different plant communities decomposed plant litter (soil quality) and how well the litter of the different plant communities decomposed under standardized conditions (litter quality).

The results showed that there are different characteristics of the plant community that drive decomposition. The nutrient concentration (nitrogen and calcium) of the plant material was especially important, while physical characteristics (leaf dry matter and fibres content) also mattered but had a smaller effect on decomposition. The soils under the different plant communities did not vary much in their ability to decompose litter. This suggests that most effects of nitrogen enrichment on decomposition occur because nitrogen favours plant species that produce easily decomposable litter.

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