Direct and indirect effects of nitrogen on ecosystem functioning
BORIS DOI
Abstract
Nitrogen enrichment is one of the major global change drivers. It has direct effects on ecosystems, such as a decrease in soil pH, a change in soil microbial properties, which affect the functions delivered. Nitrogen can also have indirect effects through a change in the biotic communities. It decreases plant species number and shifts the plant functional composition from slow growing to fast growing strategies. In addition, nitrogen also affects higher trophic levels such as foliar fungal pathogens. These indirect effects also affect ecosystem functions. However, direct and indirect effects are happening simultaneously in observational setups, and we know little about their relative importance. To investigate this, we set up “PaNDiv”, a large grassland field experiment factorially manipulating nitrogen addition, species richness, functional composition, and pathogens removal (with fungicide) on 336 plots of 2 m x 2 m.
This thesis focuses on three chapters within this framework. First, we show how nitrogen, fungicide and functional composition of the plant community affect the biodiversity-multifunctionality relationship, and we highlight the interactive effect between species richness and fast-slow functional composition. Second, we disentangle the different mechanisms by which nitrogen directly and indirectly affects litter decomposition and show that litter quality was more important than soil quality. Third, we tested the relative importance of intraspecific variation in traits compared to abundance shifts. We found that intraspecific variation of functional traits is as large as variation in abundance to explain community composition, but that intraspecific variation does not affect ecosystem functioning. Overall, this thesis provides a deeper understanding of the different and interactive mechanisms by which nitrogen addition affects the functioning of ecosystems.
This thesis focuses on three chapters within this framework. First, we show how nitrogen, fungicide and functional composition of the plant community affect the biodiversity-multifunctionality relationship, and we highlight the interactive effect between species richness and fast-slow functional composition. Second, we disentangle the different mechanisms by which nitrogen directly and indirectly affects litter decomposition and show that litter quality was more important than soil quality. Third, we tested the relative importance of intraspecific variation in traits compared to abundance shifts. We found that intraspecific variation of functional traits is as large as variation in abundance to explain community composition, but that intraspecific variation does not affect ecosystem functioning. Overall, this thesis provides a deeper understanding of the different and interactive mechanisms by which nitrogen addition affects the functioning of ecosystems.
Date of Publication
2024
Year of graduation
2020
Theses Type
dissertation
Language(s)
en
Author(s)
Faculty/Graduate School
Institute
Access(Rights)
open.access
Primary OA Publication
true