Testing the potential of priority effects to sustainably increase community function in semi-natural grasslands

A long lasting yet still ongoing debate in community ecology is the question on what are the prevalent forces which drive community assembly. Although ecologists agree that environmental factors are of importance in structuring (plant-) communities many studies found evidence for stochastic events (e.g. disturbance and the subsequent recolonization of a habitat) being the major driver during community assembly. One specific aspect of stochastic events which particularly involve the sequence in which species arrive and (in further) interact at a certain location are called priority effects. The topic of this dissertation is the investigation of priority effects in plant communities, more detailed, the potential for priority effects to influence central European semi-natural grasslands in terms of functionality (biomass production), species composition and the interplay of both. This has implications for the general understanding of (plant-) community assembly, restoration practise, and land management as well as for conservation of central Europe’s semi-natural grasslands. This dissertation project aims at using knowledge from ecological research which has been gathered over the last decades and its application of recent concepts originating from community ecology, biodiversity research, plant ecology and agricultural practise. For this purpose, several experimental approaches were applied (ranging from greenhouse- to field experiments, see chapter “A ladder of experiments”) which aim to elucidate the effects and the underlying mechanisms through which priority effects may influence model plant communities (both, artificial and semi-natural grasslands). At the same time, each one of these experiments involved at least another factor added to the design to further elucidate the quality of mechanisms responsible for the impact of priority effects on (model-) ecosystem function. Within the four papers included in this dissertation priority effects are induced by either the sowing of different starting communities (and community size) or by an experimental variation of arrival times of different plant functional types (PFTs: legumes, forbs, grasses). Thereby I point out, that an increase in 2 community productivity can be achieved as a result of priority effects by sowing legumes prior to other functional groups. And, that this effect is stronger than effects of increased sowing density or time interval between sowing events. After these insights were obtained from greenhouse experiments with model communities, priority effects induced by a variation in arrival time of PFTs were tested under field conditions, in regard to community assembly. I could show that the increase in aboveground productivity (when legumes were sown first) was a result of different community biomass allocation patterns between above- and belowground plant parts as a result of the varying order of arrival of PFTs. Thus, there was interplay of belowground asymmetric competition leading to aboveground asymmetric competition in the course of initial community assembly. Additionally, this effect was independent from differences in soil conditions hinting at a higher importance of stochastic events for community assembly. It can be concluded that the increased productivity of plots with legumes sown first (for the greenhouse experiment as well as for the field experiment) was rather due to the observed differences in biomass allocation than due to direct or indirect nitrogen facilitation because effects of nitrogen facilitation on productivity would have been stronger if sown density of legumes increased. Since this was not the case in the greenhouse experiment mentioned before (where sown density was a factor) nitrogen facilitation seems to not play an essential role during initial community assembly. Additionally, there was no evidence for any positive effect of legume presence on N concentrations (neither in plant material nor in soil samples) or growth rates of legume neighbours in another experimental setup directly aimed at this question. The results of this thesis enable us to see community assembly not only as the process (or a sum of many different processes) resulting in the patterns we observe when looking at the structure of plant communities. If well understood, priority effects can be used to steer and direct community development into desired trajectories. This could be shown within the methodical boundaries of this thesis, however further research in this direction is necessary to investigate the plasticity of priority effects under different environmental conditions, ecosystems and/or between different organisms.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2015

Author dc:creator

• Gillhaußen, Philipp von

Contributors dc:contributor

• Beierkuhnlein, Carl

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/2635/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:2635