field study; community ecology; plant community; AMF; mycorrhiza; small-scale; pyrosequencing; null model; variance partitioning
The study of assembly of plants and microbial communities is an important subject of ecological research as it aids our understanding of species diversity and hence ecosystem functions. Mycorrhizal fungi are of particular importance due to their role as prime symbionts for most land plants. The community composition of plants and mycorrhizal fungi are governed by environmental, spatial and biotic patterns, whose individual contributions are an active field of research and ongoing debate. Since the processes are tightly interwoven, greenhouse experiments offer limited access to the actual processes which take place in nature.
In the present dissertation, the community assembly rules of plants, AMF and the interplay between the two organism groups were studied in a high diversity ecosystem in the "Oderhänge Mallnow", offering a large diversity of plants and steep gradients in soil environmental properties on a small scale. Two field samplings were conducted, one studying a single macroplot of 15x15m and analyzing the AM fungi community composition of the focal plant on the study site, Festuca brevipila roots and surrounding soil. The second sampling was conducted 6 months later, using three macroplots of 15x15m, 12x12m and 12x12m, and focused on AMF communities in root and soil of Festuca brevipila plus the composition of the surrounding plant communities.
In Chapter II, the plant community assembly patterns were studied. It was found that important roles of environmental factors that prevail at larger scales also are present at smaller scales. Additionally, biotic interactions causing species segregation and effects of the spatially structured environment share a significant influence in plant community composition.
In Chapter III, the AM fungal communities from the first sampling and their respective assembly patterns were analyzed. Results indicate that environmental influences are negligible for AMF, but rather spatial and phylogenetic patterns dominate the assembly of communities. Phylogenetic clustering was observed not only in the dominant but also in the rare species, indicating that trait conservatism and resulting selection principles are a main route for AMF community assembly. Apart from this, dispersal limitation and stochastic position events contribute to the composition of an AMF community at a given spot, as evident due to the low mobility of AM fungi in the soil. These patterns may be related to direct or indirect positive interactions among fungi and their biotic environment.
In Chapter IV, the interactions of AMF and plant communities from the second sampling were analyzed in context of the Passenger and Driver framework. AMF follow their strong spatial structure and phylogenetic sorting patterns, albeit strong phylogenetic clustering could not be observed in this particular sampling, indicating potential seasonal influences. They only have insignificant influence on either their surrounding plant community composition or their phylogenetic distribution, hence rejecting the Driver hypothesis. Environment only has minor influences on AMF community composition, confirming findings from Chapter III. The plants follow more or less the same patterns as in Chapter II, even when adding AMF communities as explanatory variables to the equation. They do however have a significant influence on AM fungi community composition in context of generalized linear models, indicating evidence for the Passenger hypothesis.
In summary, plant and AMF may share a close mututalistic relationship, however, the rules governing diversity and composition of their respective communities seem to be independent of each other. While plants follow classical niche-partitioning based systematics, AMF possess a stronger focus on biotic patterns, be it intra-specific as shown by phylogenetic sorting, or inter-specific as in their influence by plants. Their low mobility and limited dispersal capabilities add a layer of random spatial position, leading to the conclusion that there is no single rule of acquisition regarding AM fungi community and diversity in an ecosystem.
List of figures iv
List of tables v
Chapter I: General Introduction 1
Chapter II: Plant community assembly at small scales: spatial vs. environmental factors in a European grassland 14
Chapter III: Arbuscular mycorrhizal fungal communities are phylogenetically clustered at small scales 39
Chapter IV: Does neighborhood plant community structure affect the arbuscular mycorrhizal fungal community of focal plants at small spatial scales? 69
Chapter V: General discussion 97
Chapter VI: Summary 107
Contributions to the publications 112
Appendix A: Supplementary Material for Chapter II 113
Appendix B: Supplementary Material for Chapter III 122
Appendix C: Supplementary Material for Chapter IV 131
Curriculum vitae 140
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