Chemical Effects of a Dominant Grass on Seed Germination of Four Familial Pairs of Dry Grassland Species
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Seed Science Research (2008) 18, 239–248 doi:10.1017/S0960258508096190 Chemical effects of a dominant grass on seed germination of four familial pairs of dry grassland species Eszter Ruprecht1*, Tobias W. Donath2, Annette Otte2 and R. Lutz Eckstein2 1Department of Taxonomy and Ecology, Babes¸-Bolyai University, Republicii street 42, RO-400015 Cluj Napoca, Romania; 2Department of Landscape Ecology and Resource Management, Interdisciplinary Research Centre, Justus-Liebig-University Gießen, Heinrich-Buff-Ring 26-32, DE-35392 Gießen, Germany Abstract Introduction Community composition and ecosystem processes Community assembly during succession may be during succession may be driven partly by traits of regulated by: (1) environmental conditions and plant species that attain dominance. Here, we resources; (2) chance events; and (3) biotic interactions addressed the hypothesis that Stipa pulcherrima, the (Weiher and Keddy, 1999). Through the traits of dominant grass of abandoned continental grasslands, dominant species, the outcome of biotic interactions controls seedling recruitment of co-occurring species (herbivory, competition, facilitation) may, in turn, feed through chemical effects of its litter. Eight species with back on abiotic conditions and resource availability, successful and unsuccessful recruitment under field and strongly determine the further development of the conditions were selected (four familial pairs) to study system. One model system that is currently undergoing experimentally the effects of leaf leachate under four great change is European semi-natural grassland, temperature regimes. Since fungi developed in which carries an exceptionally high diversity of plants leachate-treated Petri dishes, in another experiment (e.g. Ellenberg, 1988; Korneck et al., 1998). Diversity and seeds were surface sterilized to remove confounding composition of these ecosystems evolved under the effects of fungi on recruitment. Leachate affected prevailing site conditions (Vandvik and Birks, 2002), various stages of seedling recruitment: it significantly but also in response to continuous human activity over reduced seed germination (by 33–94%) and radicle millennia (Ellenberg, 1988; Pa¨rtel et al., 1996). elongation, and it delayed germination of seedlings of Consequently, their characteristic species are adapted all species. In two families, species with unsuccessful to human land use, and grassland diversity is strongly field recruitment were more negatively affected than related to past and current management practices the successful ones. In a third family, the species with (Waldhardt and Otte, 2003; Wellstein et al., 2007). With successful recruitment was more negatively affected, agricultural abandonment and intensification, plant and in the fourth there were no differences. Similar diversity in semi-natural grassland communities germination responses after exclusion of fungi through seed-surface sterilization suggested that leachate changes dramatically (Korneck et al., 1998; Luoto et al., was responsible for the observed effects on recruit- 2003; Mitchley and Xofis, 2005; Pyka¨la¨ et al., 2005; ment. Besides other traits and physical/microclimatic Wellstein et al., 2007; Enyedi et al., 2008). The resulting effects of accumulating litter, S. pulcherrima influ- decrease in species numbers is mainly due to: (1) ences plant community dynamics and may potentially increasing cover and biomass of a few highly affect ecosystem processes through its secondary productive species, which exert strong competitive compounds. effects on subordinate species; and (2) the accumu- lation of dead plant remains, i.e. litter, which interferes Keywords: allelochemicals, allelopathy, community with seed germination and seedling establishment dynamics, fungi, radicle length, seedling establishment, (Bosy and Reader, 1995; Vira´gh and Bartha, 1996; Stipa grassland, Stipa pulcherrima Bakker and Berendse, 1999; Kahmen et al., 2002; Moog et al., 2002). Litter may affect seed germination by its effects on microclimate, by acting as a mechanical barrier or through chemical effects (Facelli and Pickett, *Correspondence 1991; Bosy and Reader, 1995; Jensen and Gutekunst, Fax: þ 40 264431858 2003; Eckstein and Donath, 2005). Since these effects are Email: ruprecht@grbot.ubbcluj.ro litter-type specific, the dominant plant species may 240 E. Ruprecht et al. exert a strong influence on germination and succession abandonment of these grasslands are: (1) strong (Myster, 2006; Quested and Eriksson, 2006; Quested dominance by Stipa pulcherrima; (2) litter accumulation; et al., 2007; Donath and Eckstein, 2008), but also on (3) vegetation composition changes; and (4) decrease of ecosystem processes (Wardle et al., 1998). plant species diversity (Enyedi et al., 2008). Under The regeneration of plants from seeds is a process several experimental treatments, consisting of litter that can be broken down into several conditional and/or biomass removal, establishment success of components, such as reproductive fertility and seed certain species was very low (see Table 1; Ruprecht et al., production, seed viability, germination, seed resource- in preparation), although there were no indications of based initial seedling growth (radicle elongation, leaf seed or microsite limitation, since plants flowered expansion), autotrophic seedling growth and estab- abundantly, and various types of potential safe sites for lishment. As such, it is a particularly vulnerable stage germination and establishment were created by the in the life cycle of many plant species, and the treatments. Anothergroup of dry grassland species with suppression of seedling recruitment can have serious abundant flowering and seed production established consequences for population viability and species successfully under the same experimental conditions diversity (e.g. Tilman, 1993). In this context allelopathy, (see Table 1). Therefore, we investigated experimentally i.e. the leaching or volatilization of phytotoxins from the possible chemical effects of the dominant species, plant tissues, is considered as one possible mechanism Stipa pulcherrima,onthegerminationofsevenco- acting on seed germination (Baskin and Baskin, 2001), occurring dry grassland species and on itself at two but also on seedling establishment (Schlatterer and constant and two fluctuating temperature regimes. Tisdale, 1969; Chang-Hung and Chiu-Chung, 1975; Previous studies addressing chemical effects of litter Werner, 1975; Bosy and Reader, 1995), and plant have either used one constant (e.g. Anaya and del Amo, growth and distribution (del Moral and Cates, 1971; 1978; Bosy and Reader, 1995) or one fluctuating Rice, 1972; Newman and Rovira, 1975). Chemicals temperature regime (e.g. Rice, 1972; Norby and involved are generally secondary metabolites, Kozlowski, 1980), whereas our experimental set-up mainly simply structured, low molecular weight allowed us to address the interaction between litter compounds, such as coumarins, terpenoids, phenolics leachate and temperature across a range of conditions. or tannins (Rice, 1984; Harborne, 1993). However, Our study attempts to link potential chemical effects at since there are close links between plant secondary the population level with known transformations in compounds, palatability, litter quality and decompo- ecosystem properties in a dry grassland community as a sition (Grime et al., 1996), allelochemicals may also result of grazing abandonment. affect other components and functions of the ecosys- Our main hypotheses were that: (1) Stipa leachate tem, and thus play an important role in ecosystem reduces percentage germination, delays germination, regulation (Wardle et al., 1998; Mazzoleni et al., 2007). and interferes with radicle elongation, thus exerting Biochemical interactions differ in their strength strong negative effects on the regeneration through and may differentially affect the competitive vigour of seeds of the eight test species; and that (2) there are dominant and subordinate species. Hence, to under- species-specific differences in the response of these stand these interactions and the potential influence of various components of recruitment to leachate. (3) We dominant species on ecosystem processes, it is hypothesized that the magnitude of the effect of Stipa necessary to identify plant species in a community leachate is related to the germination success under with strong allelopathic effects on other species field conditions, i.e. the negative effects are more (Chang-Hung and Chiu-Chung, 1975; Anaya and del pronounced in species with unsuccessful than in those Amo, 1978; Anderson et al., 1978), but it is equally with successful field recruitment. important to reveal the differential susceptibility of community constituents to these toxins (Datta and Sinha-Roy, 1975; Wardle et al., 1993). Materials and methods Preliminary results of a manipulative field exper- iment on abandoned grasslands from the Transylvanian Species selection lowlands of Romania (Ruprecht et al.,inpreparation) suggested that secondary compounds of the dominant Eight grassland species, which are typical constituents grass may, among other factors, drive community of dry steppe-like grasslands of the Transylvanian assembly and succession through strong negative Lowland (Romania), were selected for laboratory seed effects on the recruitment of a number of co-occurring germination experiments, based on the results of plant species. These species-rich, dry, steppe-like previous field experiments (Table 1). The