Hartnett, David C. , N'Guessan, Maipelo .
Diffferential responses to defoliation in little bluestem (Schizachrium scoparium) in tallgrass prairie: Implications for herbivory tolerance.
The effects of herbivory on plant growth, reproduction, and morphology are complex. In grasses, traits such as relative growth rate (RGR), seed reproduction, vegetative reproduction, resource allocation, and architecture vary differentially and often non-linearly with grazing frequency or intensity. High grazing tolerance may be achieved through compensatory photosynthesis and leaf growth, or through demographic mechanisms such as activation of a belowground bud bank (dormant meristems). The objectives of this study were to assess the relationship between grazing intensity and responses of Schizachyrium scoparium (little bluestem) in tallgrass prairie, and to examine the roles of compensatory growth, reproduction, and bud banks (meristems density) in the persistence of this dominant grass under grazing. Genets were subjected to a wide range of simulated grazing intensities over a 2-yr period. Strong differential responses were observed among plant traits. RGR and plant biomass showed strong non-linear reductions and flowering declined linearly in response to increasing clipping intensity, showing no evidence of compensation. By contrast, meristems density was unaffected, and plants maintained a large bud bank (> 6 dormant buds per tiller) across all clipping treatments. Tiller natality per genet decreased with 1 to 4 clippings, but then increased with additional clippings suggesting that, with relatively intense defoliation, declines in tiller RGR are partially offset by activation of dormant buds and increasing tiller natality. In addition, increased grazing intensity resulted in the differential activation of buds at different positions (emerging within vs. outside the subtending leaf sheath), explaining the strong shift to a more prostrate growth form observed in many caespitose grasses under persistent grazing. Thus, although this grass species lacks the capacity for compensatory foliage re-growth, the maintenance of a large dormant bud bank and the differential activation of buds in different positions contribute to its grazing tolerance and avoidance respectively, and its long-term persistence in grazed grasslands.
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1 - Kansas State University, Division of Biology, 104 Ackert Hall, Manhattan, KS, 66506, USA
Presentation Type: Poster:Posters for Sections
Location: Hall A/Convention Center
Date: Monday, August 2nd, 2010
Time: 5:30 PM