COMPETITION AND FACILITATION AMONG GRASSLAND PLANTS - THE ROLE OF ARBUSCULAR MYCORRHIZA - Dissertation zur Erlangung des akademischen Grades Doktor der Naturwissenschaften (Dr. rer. nat.) - Fakultät für Biologie Universität Bielefeld vorgelegt von Ingo Höpfner Bielefeld, Dezember 2014 INDEX I INDEX ACKNOWLEDGEMENTS .............................................................................................................. V INDEX OF ABBREVIATIONS ....................................................................................................... VII SUMMARY ................................................................................................................................... 1 ZUSAMMENFASSUNG .................................................................................................................. 3 CHAPTER 1 - GENERAL INTRODUCTION ................................................................................... 5 1.1 Strategies of nutrient acquisition in grassland plants ................................................... 5 1.1.1 Root 'autonomous' strategies of nutrient acquisition ............................................ 6 1.1.2 Nutrient acquisition strategies involving mutualists ............................................. 6 1.1.2.1 AMF-mediated nutrient acquisition ............................................................... 7 1.2 Implications of root- and AMF-mediated nutrient acquisition for competitive interactions between grassland plants ................................................................................ 8 1.2.1 The role of roots in competition for nutrients ....................................................... 9 1.2.2 The role of mycorrhiza in competition for nutrients ........................................... 10 1.2.2.1 AMF-mediated vs. root-mediated nutrient depletion: relevance of mycotrophy levels for the competitive ability of a plant .......................................... 10 1.2.2.2 Plant-plant interactions via common mycelial networks ............................. 11 1.3 Concept of investigation ............................................................................................. 13 CHAPTER 2 - OBLIGATE MYCOTROPHY: CAN A STRONGLY MYCORRHIZA-MEDIATED FORAGING STRATEGY SERVE AS AN EFFECTIVE MECHANISM IN INTERSPECIFIC COMPETITION? ......................................................................................................................... 15 2.1 Abstract ...................................................................................................................... 15 2.2 Introduction ................................................................................................................ 15 2.3 Materials and methods ............................................................................................... 18 2.3.1 Experimental design ............................................................................................ 18 2.3.2 Growth conditions and plant nutrition ................................................................ 19 2.3.3 Harvest and data processing ................................................................................ 19 2.3.4 Statistical analyses ............................................................................................... 20 2.4 Results ........................................................................................................................ 21 2.4.1 Species-specific traits (single plants) .................................................................. 21 INDEX II 2.4.2 Competitive interactions between both species................................................... 24 2.5 Discussion .................................................................................................................. 25 2.5.1 Species-specific traits and foraging strategies..................................................... 25 2.5.2 Relevance of the different foraging strategies in competitive interactions ......... 27 2.6 Conclusions ................................................................................................................ 30 2.7 Authors contributions ................................................................................................. 31 CHAPTER 3 - POTENTIAL ADVANTAGES OF HIGHLY MYCOTROPHIC FORAGING FOR THE ESTABLISHMENT OF EARLY SUCCESSIONAL PIONEER PLANTS ON SAND................................. 32 3.1 Abstract ...................................................................................................................... 32 3.2 Introduction ................................................................................................................ 32 3.3 Materials and methods ............................................................................................... 34 3.3.1 Plant cultivation ................................................................................................... 34 3.3.2 Determination of root and hyphal surface area growth rates .............................. 35 3.3.3 Determination of soil P depletion rates ............................................................... 36 3.3.4 Quantification of mycorrhizal root colonization ................................................. 37 3.3.5 Assessment of mycorrhizal growth dependency and plant tissue P concentration ................................................................................... 37 3.3.6 Statistical analyses ............................................................................................... 38 3.4 Results ........................................................................................................................ 38 3.5 Discussion .................................................................................................................. 46 3.5.1 Contrasting dependencies on presence of AMF for P uptake and growth .......... 46 3.5.2 Species-specific C allocation trade-off between roots and AMF ........................ 47 3.5.3 Relevance of different C-allocation patterns for soil P depletion ....................... 49 3.6 Conclusions ................................................................................................................ 51 3.7 Authors contributions ................................................................................................. 51 CHAPTER 4 - INTRA- AND INTERSPECIFIC SEEDLING FACILITATION VIA COMMON MYCELIAL NETWORKS IN HIERACIUM PILOSELLA AND PLANTAGO LANCEOLATA ................... 52 4.1 Abstract ...................................................................................................................... 52 4.2 Introduction ................................................................................................................ 52 4.3 Material and Methods ................................................................................................. 55 4.3.1 Experimental setup .............................................................................................. 55 4.3.2 Plant cultivation ................................................................................................... 56 4.3.3 Determination of net large plant effects on seedling growth .............................. 57 4.3.4 Fungal measurements .......................................................................................... 58 INDEX III 4.3.5 Statistical analyses ............................................................................................... 59 4.4 Results ........................................................................................................................ 59 4.5 Discussion .................................................................................................................. 65 4.5.1 CMN-mediated facilitation of seedlings by H. pilosella large plants ................. 65 4.5.2 Effects of P. lanceolata large plants on CMN-mediated seedling facilitation .... 66 4.6 Conclusions ................................................................................................................ 68 4.7 Authors contributions ................................................................................................. 69 CHAPTER 5 - INVESTIGATING THE MECHANISMS OF CMN-MEDIATED SEEDLING FACILITATION: RELEVANCE OF SEEDLING CMN-COSTS, LARGE PLANT SPECIES IDENTITY AND COMPETITIVE EFFECTS FOR THE NET OUTCOME OF FACILITATION............... 70 5.1 Abstract ...................................................................................................................... 70 5.2 Introduction ................................................................................................................ 71 5.3 Material and Methods ................................................................................................. 74 5.3.1 Growth conditions and experimental set-up ........................................................ 74 13 5.3.2 CO2 pulse-labeling ............................................................................................ 77 13 5.3.3 Quantification of CO2 assimilation using the 'CRDS-CFI' approach ............... 79 5.3.4 Measurement of seedling-assimilated carbon in soil respiration and estimation of seedling-C transfer via mycorrhizal hyphae within the CMN ............... 80 5.3.5 Final harvest and analysis of plant and fungal material ...................................... 81 5.3.6 Estimation of C allocation in seedling and fungal solid matter .......................... 82 5.3.7