Competition and coexistence in grassland codominants: responses to neighbour removal and resource availability

Abstract

We examined the role of interspecific competition in the regulation of abundance and coexistence of the dominant grasses in tallgrass prairie using a removal experiment with Andropogon gerardii Vitman and Sorghastrum nutans L. Nash, two of the most abundant grasses in tallgrass prairie. Plant removal treatments (using foliar herbicide), applied to 0.3-m2 plots at the Konza Prairie Biological Station (northeast Kansas, USA), included removal of all A. gerardii, removal of all S. nutans, and no removal. To determine whether soil fertility altered the outcome, we included a fertilizer addition treatment (10 g N·m–2) fully crossed with the removal treatments. Andropogon gerardii removal resulted in significantly increased net photosynthesis, stomatal conductance, and tiller mass in S. nutans. Sorghastrum nutans removal had little effect on A. gerardii, suggesting asymmetric competition. Fertilizer significantly increased tiller mass and flowering stalk production in S. nutans, but had little effect on A. gerardii. The ability of A. gerardii to suppress the performance of S. nutans is consistent with the greater abundance of A. gerardii over much of the tallgrass prairie, while the ability of S. nutans to take advantage of increased resources may be one mechanism by which it avoids competitive exclusion. Because of the greater variability in the performance of S. nutans than in that of A. gerardii, any natural or anthropogenic alterations to this grassland that lead to shifts in dominance between these species may affect ecosystem productivity and stability.Key words: Andropogon gerardii, competition, grassland, neighbour removal, photosynthesis, Sorghastrum nutans, tallgrass prairie.

Short‐term effects of elevated precipitation and nitrogen on soil fertility and plant growth in a Neotropical savanna

“…Water addition led to high flowering probability and increased numbers of spikelets and potentially seed number for Loudetiopsis, while nitrogen addition was negatively correlated with flowering for Tristachya and uncorrelated with reproductive traits in Loudetiopsis. This result contrasts with previous research that strongly links N addition with higher rates of grass flowering in a temperate grassland (Silletti et al 2004).…”

“…2). These species-specific responses, comparable to those observed in other studies of cooccurring C-4 grasses (Silletti and Knapp 2001, Silletti et al 2004, Fynn et al 2005, also suggest particular species traits which could be responsible for the differences in response to simulated global change factors. The most notable of these is drought tolerance, which could influence leaf senescence response to water addition (see also Swemmer et al 2006).…”

How does the precipitation gradient interact with common disturbances to structure prairies?

“…Knapp et al 1998;Myster 2011). Much of that research has focused on changes of resident prairie plants over space and time (Collins and Adams 1983;Polley and Collins 1984;Collins and Uno 1985;Glenn and Collins 1993;Risser et al 1994;Briggs et al 1998;Howe and Brown 1999;Silletti et al 2004).…”

Plant and arthropod diversity in prairie restorations around Louisville, KY.

“…These groups were chosen due to their morphological and physiological characteristics as well as their varying roles in a prairie ecosystem as host plants for herbivores and also as their role in creating microhabitats for the animals that live in prairies (Symstad 2002). Grasses and forbs are the dominant groups in prairies (Howe 1994, Silletti et al 2004, and legumes are important in restorations due to their ability to fix nitrogen, often a limiting resource in prairie restorations ).…”

“…Traditionally, tallgrass prairies are thought of as being dominated by a few key warm-season C 4 species such as Andropogon gerardii (Big Bluestem), Panicum virgatum (Switchgrass), Sorghastrum nutans (Yellow Indiangrass), and Schizachyrium scoparium (Little Bluestem), as well as many forbs in the Lamiaceae (Mint) and Asteraceae (Sunflower) families (Howe 1994, Silletti et al 2004. A high quality prairie also has a large abundance of sedges and is inhabited by hemiparasites (Howe 1994, Sivicek andTaft 2011).…”