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Accueil du site → Doctorat → États-Unis → 1987 → Competition and coexistence between two C(4) grasses of the shortgrass steppe

Colorado State University (1987)

Competition and coexistence between two C(4) grasses of the shortgrass steppe

Turner, Sandra Jeanne

Titre : Competition and coexistence between two C(4) grasses of the shortgrass steppe

Auteur : Turner, Sandra Jeanne

Université de soutenance : Colorado State University

Grade : Doctor of Philosophy (PhD) 1987

The shortgrass steppe is a semiarid grassland dominated by Bouteloua gracilis and Buchloe dactyloides. The steppe environment is subjected to precipitation patterns that are highly variable both among years and seasons. Water is the single most important factor that segregates species into life forms and photosynthetic pathways. This study of water used by two similar C$\sb4$ grasses did not support a theory of water as a major factor that separated them. Leaf water potential, diffusive resistance and transpiration of the grasses, Bouteloua gracilis and Buchloe dactyloides, were investigated in field, common garden and greenhouse studies. These parameters were found to be unaffected in either species by the presence of the other when the two species were grown together. Growth patterns and harvested biomass of B. gracilis and B. dactyloides were, likewise, unaffected by growth in a mixture in the field or common garden environments. Reduction of some biomass parameters of B. dactyloides and total yields were recorded in the greenhouse study when it was in mixed plantings with B. gracilis. This effect may have resulted from the density of the plantings in the greenhouse, rather than competition. Clipping and soil water regime were not found to exacerbate a competitive relationship between the two species. The data of biomass and water parameters did not demonstrate a significant (P $>$ 0.10) interaction between clipping and soil water regime. These studies did not show significant statistical differences in water use and growth parameters between the two grasses when grown in pure or mixed cultures. This, together with historical data, suggests that the patterns we observe within the C$\sb4$ grass component of the shortgrass steppe are related to differential survival patterns of the two grasses, rather than to direct resource competition leading to Gausian exclusion.

Mots clés : Ecology, Biological sciences

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