Assessing Fine-Scale Genotypic Structure of a Dominant Species in Native Grasslands

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ABSTRACT.-

Genotypic diversity of dominant species has been shown to have important consequences for community and ecosystem processes at a fine spatial scale. We examined the fine-scale (i.e., plant neighborhood scale, <1 m^sup 2^) genotypic structure of Andropogon gerardii, a dominant species in the tallgrass prairie, which is a productive and endangered grassland ecosystem, employing the commonly used amplified fragment length polymorphism (AFLP) technique. In this paper we used two methods to assess the fine-scale genetic spatial structure of a dominant perennial grass, (1) we determined how many tillers to sample in a 1 m^sup 2^ area and (2) we developed AFLP markers that would differentiate between genotypes. By determining appropriate sampling and molecular techniques, our findings can be applied to questions addressing how genetic diversity of dominant species affect ecosystem processes in the tallgrass prairie.

INTRODUCTION

Diversity at all levels, whether it is species diversity of a community or genotypic diversity of a species within a community, is crucial to understanding the functioning of ecosystems (Tilman et al, 1997; Whitham et al, 2003; Whitham et al, 2006). Recently, there has been increasing focus on genotypic diversity of dominant species, as genotypic diversity within these species has been shown to have important consequences for a range of ecosystem processes (Bailey et al., 2009). Studying dominant species is highly relevant because they contribute disproportionately to biomass production and structure the biotic community (McNaughton and Wolf, 1970; Grime, 2001). More recently, the genotypic diversity within a single dominant species at a fine scale (i.e., within a 1 m^sup 2^ plot) has been shown to impact productivity (Crutsinger et ai, 2006), neighborhood species interactions (Booth and Grime, 2003; Fridley et ai, 2007), resistance and resilience to disturbance (Hughes and Stachowicz, 2004; Reusch et al, 2005), trophic interactions (Crutsinger et al, 2006; Johnson et al, 2006) and resistance to invasion (Crutsinger et al, 2008).

North American tallgrass prairie is a productive, endangered ecosystem with an estimate of 1-18% intact prairie remaining (Samson and Knopf, 1994). In the tallgrass prairie, Andropogon gerardii Vitman (big bluestem) is a dominant native C4 grass (Weaver, 1954). As a dominant species, it is widespread (i.e., range extends across the United States west of the Rocky Mountains) and often locally abundant (e.g., Smith and Knapp, 2003). Further, A. gerardii has been shown determine plant community diversity and drive ecosystem function, accounting for as much as 80% of primary productivity when highly abundant (Smith and Knapp, 2003).

Andropogon gerardii is a rhizamatous, clonal grass that forms relatively dense stands of tillers (individuals) , in which a number of other grass and forb species are intermixed. At the scale where individual tillers compete with one another and with individuals of other plant species - the plant neighborhood scale (i.e., <1 m^sup 2^) - A. gerardii tillers can account for as much as 80% of the individuals (Smith and Knapp, 2003). Thus, on the basis of its high number of individuals alone, there is the potential for variation in the number and abundance of genotypes of A. gerardii at the plant neighborhood scale. Indeed, studies at larger spatial scales (> 1 to 10 m^sup 2^) have found high intra-population genetic variation within stands of A. gerardii (Gustafson et al,, 1999; Keeler el al., 2002). However, studies are lacking assessing genotypic variation a finer scales (i.e., within a 1 m^sup 2^ plot). This is despite the growing evidence that fine-scale genotypic variation can impact both community and ecosystem processes, as has been shown for other dominant and clonal plant species (e.g., Booth and Grime, 2003; Crutsinger et al., 2006).

In this paper, our objective was to assess, for the first time, the fine-scale genotypic variation of Andropogon gerardii in intact tallgrass prairie. …