STOMATAL CONTROL, XYLEM HYDRAULICS AND LEAF MORPHOLOGY IN THE 40 BEF-CHINA TREE SPECIES: TRAIT INTERRELATIONSHIPS, FUNCTIONAL DIVERSITY AND TREE GROWTH PREDICTION Kumulative Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften (Dr. rer. nat.) der Naturwissenschaftlichen Fakultät I Biowissenschaften der Martin-Luther-Universität Halle-Wittenberg vorgelegt von Herrn Diplom-Biologen Wenzel Kröber geboren am 30.10.1982 in Halle (Saale) Gutachter 1. Helge Bruelheide 2. Stan Harpole 3. Karsten Wesche Datum der Verteidigung: 24.02.2015 “My precious” John Ronald Reuel Tolkien (1937) Copyright notice Chapters 2 to 5 have been either published in or submitted to international journals. Copyright is with the authors. Reprint of the presented material requires the authors’ permissions, except for chapter 3, which has been published open access. Table of Contents Chapter 1 .................................................................................................................................... 1! 1.1 Summary .......................................................................................................................... 1! 1.2 .................................................................................................................................. 3! 1.3 Zusammenfassung ............................................................................................................ 5! 1.4 Introduction ...................................................................................................................... 7! 1.4.1 How is biodiversity linked to ecosystem functioning? ............................................. 7! 1.4.2 Plant functional traits ................................................................................................. 8! 1.4.3 Are ecosystem functions better explained by the environment, by community weighted means or by functional diversity? ............................................................ 14! 1.5 Objectives of the thesis ................................................................................................... 16! 1.5.1 Outline ..................................................................................................................... 17! 1.5.2 Hypotheses tested in the thesis ................................................................................ 19! 1.6 References ...................................................................................................................... 21! Chapter 2 .................................................................................................................................. 29 Transpiration and stomatal control: a cross-species study of leaf traits in 39 evergreen and deciduous broadleaved subtropical tree species Chapter 3 .................................................................................................................................. 47 Linking xylem hydraulic conductivity and vulnerability to the leaf economics spectrum – a cross-species study of 39 evergreen and deciduous broadleaved subtropical tree species Chapter 4 .................................................................................................................................. 75 Leaf morphology of 40 evergreen and deciduous broadleaved subtropical tree species and relationships to functional ecophysiological traits Chapter 5 .................................................................................................................................. 89 Early subtropical forest growth is driven by community mean trait values and functional diversity rather than the abiotic environment Chapter 6 ................................................................................................................................ 119! 6.1 Discussion .................................................................................................................... 119! 6.1.1 Stomatal conductance regulation ........................................................................... 120! 6.1.2 Xylem hydraulics .................................................................................................. 121! 6.1.3 Leaf microscopy traits ........................................................................................... 123! 6.1.4 Biodiversity, traits & ecosystem functioning ........................................................ 124! 6.1.5 Conclusion ............................................................................................................. 126! 6.2 References .................................................................................................................... 129! 6.3 Thanks .......................................................................................................................... 145! 6.4 Appendix ...................................................................................................................... 146! 6.4.1 Curriculum vitae .................................................................................................... 146! 6.4.2 List of publications ................................................................................................ 148! 6.4.3 Eigenständigkeitserklärung ................................................................................... 149! Chapter 1 1.1 Summary Research on biodiversity-ecosystem functioning (BEF) has undergone considerable progress especially due to lessons learned in BEF experiments lately. With 400.000 trees and shrubs planted in 566 plots and a tree species diversity gradient between 1 and 24 species per plot, BEF-China is one of the largest BEF experiments with woody plants. The present thesis consists of four papers all based on data from the BEF-China tree species. The first three studies that form part of this thesis deal with the interrelationships of plant functional traits in the 40 subtropical broadleaved tree species planted in the BEF-China experiment. Investigating the interplay between different plant functional traits, this thesis addressed the following questions: How are traits related to each other and are there any ecophysiologically determined trade-offs in different trait complexes such as xylem hydraulics and stomatal regulation parameters? Are these ecophysiological characteristics related to leaf traits captured by the leaf economics spectrum (LES)? Several new key parameters that describe stomata conductance (gS) regulation were extracted from gS-vapour pressure deficit curves. As hypothesized, traits characteristic for the LES, for example, leaf nitrogen concentration and leaf carbon-to-nitrogen ratio, were related to mean gS. Interestingly, other leaf traits not correlated with the LES, such as stomatal traits, were found to be good predictors of stomatal regulation characteristics. Water flow in vascular plants connects xylem hydraulics and leaf morphology and anatomy. The quantification of the specific xylem hydraulic conductivity and the xylem pressure at which 50% loss of the maximum specific xylem hydraulic conductivity of the study species occurs (Ψ50) revealed that cavitation resistance was closely linked to the traits of the LES, but not to any parameter of gS regulation though. Moreover, several leaf traits that typically are not considered in research, for instance, microscopy and morphologic traits such as leaf thickness, the log ratio of palisade to spongy mesophyll thickness and microstructure of the leaf surface, determined gS regulation significantly. For xylem hydraulics, however, the leaf habit overruled any further signal from other traits. Although analysis of plant functional traits represents a reliable approach in biodiversity ecology, BEF studies that would focus on the parallel analysis of the impact of biotic and abiotic effects on ecosystem functions such as productivity in forest ecosystems have been scarce so far. Thus, the dominant drivers of forest growth like the environment, the identity of 1 specific species or the magnitude of functional diversity in the respective communities have not been fully understood yet. The fourth study focused on the impact that the following factors may have on the mean tree crown increment of the experimental plots: the environmental conditions, community weighted mean (CWM) traits or functional diversity. The trait values aggregated in CWM displayed the biggest effect on the variation in productivity of the forest plots; FD scored medium impact whereas the environment, contrary to expectation, had only a very limited impact. Thus, already at an early stage of the experiment, biotic influences overruled effects from the environmental setting. Summing up, this thesis provides deeper insight into stomatal control and contributes to the knowledge about xylem vulnerability and morphological proxies for physiological leaf traits. In addition, a framework to predict ecosystem functioning was tested and environment was found to be the least important parameter. The results of this thesis demonstrate that the specific plant functional traits employed in BEF research should be chosen carefully in order to maximize methodological efficiency and to minimize unwanted data redundancy. 2 1.2 BEF- ChinaBEF566 4024 BEF-China40 40 - LES 3 BEF 4 1.3 Zusammenfassung Die Biodiversitätsforschung auf ökosystemarer Ebene hat vor allem durch Erkenntnisse aus Experimenten, die den Zusammenhang zwischen Diversität und Ökosystemfunktionen untersuchen, beträchtliche Fortschritte