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Cheatgrass (Bromus tectorum L.) has come to dominate millions of hectares of rangeland in the Intermountain western United States. Previous studies have hypothesized that one mechanism conferring a competitive advantage to this species is the ability to germinate rapidly at low temperatures in the fall, winter and spring and, therefore, initiate growth and establishment more rapidly than more desirable perennial bunchgrass species. In this experiment, we developed thermal-germination-response models for multiple seedlots of cheatgrass and five perennial grass species. We conducted sensitivity analysis on potential-cumulative-germination response to a 38-year simulation of field-variable conditions of seedbed temperature...
At the Appleton-Whittell Research Ranch, an ungrazed grassland preserve in southeastern Arizona, soil seed banks were sampled in June, August, and October 2002 and June 2003. Wildfire had previously burned 90% of the research ranch in May 2002. Seed density and species richness in burned native grassland (2 plots) were compared to those in burned exotic grassland (2 plots). Averaged over 4 sample dates, seed densities were as follows: burned native grassland, 591 ± 243.1 seeds ⋅ m–2 and 784 ± 334.9 seeds ⋅ m–2; burned exotic grassland, 501 ± 198.9 seeds ⋅ m–2 and 196 ± 123.8 seeds ⋅ m–2. Species richness in the seed bank, also averaged over 4 sample dates, was as follows: burned native grassland, 16.3 ± 1.7 species...
Winterfat (Ceratoides lanata (Pursh) J.T. Howell, syn. Eurotia lanata (Pursh) Moq., syn. Krascheninnikovia lanata Gueldenstaedt) seeds possess an after-ripening requirement to break dormancy. Germination responses of winterfat seeds to ethanol, gibberellic acid (GA3), citric acid and sodium nitrate (NaNO3) were tested in the laboratory to determine their ability to break dormancy. Ethanol, GA3 and citric acid promoted, while NaNO3 inhibited germination. Ethanol promoted fast and synchronous germination. Promotion of germination by GA3 or citric acid was weak during the test period. Citric acid damaged the radicles of seedlings. Soaking winterfat seeds in 600 to 1,000 mM ethanol for 4 to 8 hours is recommended, as...
Evolutionary bet hedging encapsulates the counterintuitive idea that organisms evolve traits that reduce short-term reproductive success in favor of longer-term risk reduction. It has been widely investigated theoretically, and many putative examples have been cited including practical ones such as the dormancy involved in microbe and weed persistence. However, long-term data on demographic variation from the actual evolutionarily relevant environments have been unavailable to test for its mechanistic relationship to alleged bet hedging traits. I report an association between delayed germination (a bet hedging trait) and risk using a 22-year data set on demographic variation for 10 species of desert annual plants....
Millions of acres of rangeland in the western United States are now dominated by introduced annual weeds such as cheatgrass (Bromus tectorum L.). The ability to germinate rapidly at low temperatures has been proposed as one of many mechanisms that confer a competitive advantage to this species. Previous studies of this phenomenon, however, have been limited to relatively simple comparisons of total germinability and germination rate under selected constant-temperature treatments. In this study, we germinated seeds of cheatgrass and two native perennial bunchgrass species, bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) Löve] and big squirreltail [Elymus multisetus (J.G. Smith) M.E. Jones], over the temperature...


    map background search result map search result map Regeneration trends along climate gradients in Taxodium distichum forest of the southeastern United States, 2007-2019 Regeneration trends along climate gradients in Taxodium distichum forest of the southeastern United States, 2007-2019