Effects of mycorrhizal and plant density on yield relationships among competing tallgrass prairie grasses

TitleEffects of mycorrhizal and plant density on yield relationships among competing tallgrass prairie grasses
Publication TypeJournal Article
Year of Publication1994
AuthorsHetrick, BAD, Hartnett, DC, Wilson, GT, Gibson, DJ
JournalCanadian Journal of Botany
Pagination168 -176
Accession NumberKNZ00447
KeywordsAndropogon gerardii, arbuscular mycorrhizae, de Wit replacement series, Elymus canadensis, Koeleria pyramidata

A replacement series experiment was used to investigate the effects of mycorrhizae, phosphorus availability, and plant density on competitive relationships between three tallgrass prairie species of varying mycorrhizal dependencies. Under mycorrhizal conditions, the obligately mycorrhizal dependent warm-season grass Andropogon gerardii (big bluestem) was a better competitor in mixture with the nonmycorrhiza-dependent cool-season grass Koeleria pyramidata (Junegrass). In the absence of mycorrhizae, however, competitive effects of big bluestem were greatly reduced and Junegrass experienced competitive release. Relative yield totals increased when mycorrhizae were suppressed, suggesting greater intensity of interspecific competition in the presence of mycorrhizae. Thus, the competitive dominance of big bluestem in tallgrass prairie is strongly related to its mycorrhizal status. Elymus canadensis (Canada wild rye) outcompeted big bluestem both with and without mycorrhizae. Relative yield totals of this species mixture were also lower under mycorrhizal conditions, indicating that mycorrhizae increase the intensity of interspecific competition between them. Relative yields of wild rye competing with big bluestem increased in the absence of mycorrhizae, suggesting that it also experiences competitive release when big blue-stem are not mycorrhizal. The outcomes of competition were generally similar among the three total plant density treatments and between P-fertilized and nonfertilized treatments. However, interactions between mycorrhizal effects and plant density confirm that outcomes of interspecific competitive interactions may be density dependent in some cases.