1 Functional traits of salt marsh plants: responses of morphology- and elemental- based traits to environmental constraints, trait-trait relationships and effects on ecosystem properties Von der Fakultät für Mathematik und Naturwissenschaften der Carl von Ossietzky Universität Oldenburg zur Erlangung des Grades und Titels eines Doktors der Naturwissenschaften (Dr. rer. nat.) angenommene Dissertation von Vanessa Minden, geboren am 14. April 1979 in Saarlouis i Gutachter Prof. Dr. Michael Kleyer Zweitgutachter Prof. Dr. Helmut Hillebrand Tag der Disputation 14.12.2010 ii iii i Contents Contents ........................................................................................................... i Summary ......................................................................................................... v Zusammenfassung ......................................................................................... ix List of most important abbreviations ...........................................................xiii 1 Preface ...................................................................................................... 1 2 The functional approach: from traits to types ........................................... 5 2.1 The term ‘trait’ and its functionality ............................................................. 6 2.2 From functional traits to functional types ..................................................... 6 2.3 Linking the environment with ecosystem properties: effect and response traits and the role of biodiversity ............................................................................. 7 2.4 Concepts of trait-environmental relationships .............................................. 9 3 Ecological Stoichiometry ........................................................................ 15 3.1 General introduction ................................................................................... 15 3.2 Elemental composition in autotrophs in relation to tissue differentiation .. 17 3.3 Variability in C:N:P concentrations ............................................................ 18 3.4 Environmental constraints on organismal stoichiometry ............................ 19 3.5 Allocation patterns ...................................................................................... 21 4 Salt marshes ............................................................................................ 25 4.1 Abiotic conditions in salt marshes and their effects on plant performance. 26 4.2 Species composition ................................................................................... 28 4.3 Adaptations to salt stress ............................................................................ 29 4.4 Ecosystem functions in salt marshes .......................................................... 31 5 Study design and parameter-synopsis ..................................................... 35 5.1 Study sites ................................................................................................... 35 5.2 Sampling design ......................................................................................... 36 5.3 Species composition ................................................................................... 37 5.4 Abiotic parameters ...................................................................................... 37 5.5 Plant functional traits .................................................................................. 41 ii 5.6 Ecosystem properties .................................................................................. 44 6 Trait-environmental concepts are not explicitly convertible to salt marshes ......................................................................................................... 47 6.1 Introduction ................................................................................................ 48 6.2 Materials and methods ................................................................................ 51 6.3 Results ........................................................................................................ 58 6.4 Discussion ................................................................................................... 65 7 Environmental constraints on the C:N:P stoichiometry of plant organs in salt marshes ................................................................................................... 71 7.1 Introduction ................................................................................................ 72 7.2 Materials and Methods ............................................................................... 75 7.3 Results ........................................................................................................ 80 7.4 Discussion ................................................................................................... 88 8 Testing the effect-response framework: key response and effect traits determining aboveground biomass of salt marshes ...................................... 97 8.1 Introduction ................................................................................................ 98 8.2 Methods .................................................................................................... 103 8.3 Results ...................................................................................................... 110 8.4 Discussion ................................................................................................. 116 9 Plant trait responses to the environment and effects on ecosystem properties in salt marshes ............................................................................ 123 9.1 Introduction .............................................................................................. 124 9.2 Materials and Methods ............................................................................. 129 9.3 Results ...................................................................................................... 135 9.4 Discussion ................................................................................................. 141 10 Synthesis ............................................................................................... 147 10.1 General remarks ........................................................................................ 147 10.2 Environmental constraints and species distribution .................................. 147 10.3 Trait expressions of salt marsh plants as response to environmental conditions ............................................................................................................ 149 10.4 Possible soft traits as surrogates for hard traits ......................................... 150 iii 10.5 Trait-trait relationships ............................................................................. 154 10.6 Plant traits effecting ecosystem functioning and the role of biodiversity . 157 10.7 Improvements on methodology ................................................................ 158 10.8 Recommendations for further analysis and research ................................ 160 References ................................................................................................... 165 Appendix ..................................................................................................... 199 Acknowledgments ...................................................................................... 211 Curriculum Vitae ........................................................................................ 213 Erklärung .................................................................................................... 217 v Summary Loss of species diversity may not only be critical from an ethical and taxonomic point of view, but it may also have profound effects on the functioning of ecosystems. Species richness per se may indeed not be the best predictor, but rather the functional characteristics of species from a community determine ecosystem functioning most strongly. Trait expressions can be seen as a response of the organism to abiotic and biotic conditions. Interactions between traits give information about allocation patterns, i.e. the investment in one trait on the expense of another. Finally, traits show an effect on ecosystem properties, which can be used to evaluate the importance of plant trait expressions on the maintenance of various ecosystem properties. In this study, the responses of plant traits on environmental constraints were evaluated and the most responsive morphology- and elemental-based plant traits were identified and tested for their applicability to trait-environmental concepts. Trait-trait relationships were investigated and ultimately, the effects of plant traits on ecosystem properties were assessed and the role of biodiversity in the maintenance of those ecosystem properties was highlighted. The study was conducted in salt marshes along the mainland coast of Northwest Germany and on the island of Mellum. Plants inhabiting salt marshes are exposed to constantly changing environmental conditions, like periodic flooding accompanied by changes in temperature, light- and CO2- conditions or mechanical disturbance by wind and wave energy. Trait information was collected for the whole plant (including information on belowground organs) for every species of the habitat. On every plot abiotic parameters (inundation frequency, groundwater level and salinity, utilization