Using enrichment planting to test for environmental filtering and niche differentiation in grassland communities Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften (Dr. rer. nat.) der Naturwissenschaftlichen Fakultät I – Biowissenschaften – der Martin-Luther-Universität Halle-Wittenberg vorgelegt von Frau Dipl.-Biol. Eva Breitschwerdt geboren am 02.08.1980 in Mühlacker Gutachter 1. Prof. Dr. rer. nat. habil. Helge Bruelheide 2. Prof. Dr. rer. nat. habil. Isabell Hensen 3. Prof. Dr. rer. nat. Jitka Klimešová Halle (Saale), den 05.02.2019 (Verteidigungsdatum) Table of contents Summary ..................................................................................................................................... i Zusammenfassung ..................................................................................................................... iv Chapter 1 – Introduction ............................................................................................................. 1 1.1 General Introduction ......................................................................................................... 1 1.2 Objectives of the thesis ..................................................................................................... 7 1.3 Study area ....................................................................................................................... 12 1.4 References ...................................................................................................................... 20 Chapter 2 – Do newcomers stick to the rules of the residents? Designing trait-based community assembly tests ........................................................................................................ 30 2.1 Abstract .......................................................................................................................... 30 2.2 Introduction .................................................................................................................... 31 2.3 Methods .......................................................................................................................... 34 2.4 Results ............................................................................................................................ 42 2.5 Discussion ...................................................................................................................... 47 2.6 Acknowledgements ........................................................................................................ 51 2.7 References ...................................................................................................................... 51 2.8 Supporting Information .................................................................................................. 56 Chapter 3 – Using co-occurrence information and trait composition to understand individual plant performance in grassland communities ........................................................................... 57 3.1 Abstract .......................................................................................................................... 57 3.2 Introduction .................................................................................................................... 58 3.3 Results ............................................................................................................................ 61 3.4 Discussion ...................................................................................................................... 72 3.5 Materials and Methods ................................................................................................... 76 3.6 References ...................................................................................................................... 81 3.7 Acknowledgements ........................................................................................................ 88 3.8 Supplementary Information ............................................................................................ 88 Chapter 4 – Trait-performance relationships of grassland plant species differ between common garden and field conditions ....................................................................................... 89 4.1 Abstract .......................................................................................................................... 89 4.2 Introduction .................................................................................................................... 90 4.3 Methods .......................................................................................................................... 92 4.4 Results ............................................................................................................................ 95 4.5 Discussion .................................................................................................................... 102 4.6 Acknowledgements ...................................................................................................... 104 4.7 References .................................................................................................................... 105 4.8 Supporting Information ................................................................................................ 109 Chapter 5 – Synthesis ............................................................................................................. 110 5.1 Main results .................................................................................................................. 110 5.2 General discussion ........................................................................................................ 112 5.3 Conclusion .................................................................................................................... 124 5.4 References .................................................................................................................... 124 Acknowledgements ................................................................................................................ 132 Appendix ................................................................................................................................ 133 Curriculum vitae ................................................................................................................. 133 List of publications ............................................................................................................. 134 Eigenständigkeitserklärung ................................................................................................ 135 Attachment: CD (contains a PDF of the Supporting Information of chapters 2 – 4 and a PDF of the whole thesis) Summary Many grassland communities have suffered diversity loss through land-use intensification. Landscape fragmentation and a general decline of grasslands caused by abandonment or conversion from grassland to arable land lead to dispersal limitation of many plant species. Many grassland communities are therefore not saturated with species and there is the potential that new species could become established. Adding new species to existing grassland communities can give insight into the mechanisms and assembly rules behind plant community formation. The process of niche differentiation is supposed to favor plant species with dissimilar traits, whereas the process of environmental filtering is assumed to select plant species with similar traits. However, knowledge to which degree both processes impact the assembly of plant species under increasing land-use intensity is still missing. The aim of the present thesis is to investigate how similar or dissimilar new species need to be in traits in order to become established at grassland sites under varying land-use intensity. To answer the raised questions two experiments were established within the framework of this thesis: An enrichment planting experiment set up in existing grassland communities and a common garden experiment. The enrichment planting experiment was conducted on 54 grassland sites in three different regions of Germany (Schwäbische Alb, Hainich and Schorfheide) within the network of the Biodiversity Exploratories. Young transplants of 130 vascular plant species were raised in the greenhouse and planted into the experimental grasslands according to four different enrichment planting scenarios. The species of the Random scenario were selected randomly from a regional species pool. The Dissim and Sim scenarios represented species with most dissimilar and most similar traits respectively compared to the resident communities. These two trait-based scenarios were used to quantify the influence of niche differentiation and environmental filtering processes along the gradient of land-use intensity. The Beals scenario contained species with high probability of co-occurrence to the resident communities. Species of this scenario are supposed to exhibit the degree of trait similarity that reflects the searched impact of niche differentiation and environmental filtering in a community, because they grow in similar community constellations under natural conditions. The common garden experiment was set up in the Botanical Garden of the Martin Luther University of Halle-Wittenberg. The same species as in the enrichment planting experiment grew in a threefold repetition without influences of land-use and