Diaspore Characteristics and Ecological Adaptation of Bromus tectorum L. from Different Distribution Regions
2013-08-30
As one main component of global change, biological invasion is considered to be one of the primary threats to rare and endangered species, biodiversity, as well as the integrity and function of native ecosystems worldwide.
Bromus tectorum L. (Cheatgrass) is an annual grass native to Central Asia and currently found in other parts of the world, including Europe and North America. B. tectorum has become one of the most problematic invasive species in North America since its introduction in the late 19th century.
B. tectorum produces diaspores and forms a seed bank in the soil, and in drier habitats, the soil seed bank will sustain for a long time. In addition, diaspore size significantly influences seedling survival. Diaspores are among the most important reproductive organs of seed plants and are produced during an important stage of the plant life cycle. Diaspores act as a link between different generations; this role of the diaspore has vital significance on individual reproduction and population extension. Hence, diaspores under selection for studying have an important implication.
This study compares differences in seed morphology for B. tectorum collected from the United States, Kazakhstan, and Xinjiang of China. The following indices of B. tectorum diaspores were analyzed: size, thickness of covering layers, and micromorphological characteristics of the base, middle and transition area of diaspores as well as of the awn. Micromorphology of the lemma and the cross-section of the diaspore were observed by scanning electron microscopy.
Results showed that thickness of the lemma and the palea of diaspores from B. tectorum-infested grasslands in the United States were reduced (P<0.05), likely because of environmental influences. This reduction facilitated the germination of diaspores and lowered the resistance of B. tectorum to adverse environmental conditions. The length of the awn also increased significantly (P<0.05), which helped in dispersal and anchoring of diaspores. Therefore, B. tectorum adapted ecologically to its new environment in the United States by strengthening its establishment ability. However, the defense capability of B. tectorum decreased.
These results fit the evolution of increased competitive ability hypothesis (EICA) of invasive species. Analysis of various cells on the lemma revealed that prickle densities and collapsed, long epidermal cells were easily influenced by environmental factors such as temperature and moisture because of the physiologic function of these structures on silicon accumulation. However, the form and the position of silica cells, which were not greatly influenced by environmental factors, might be genetically controlled. Studying these structures at the microscopic level helps define the relationship between the diaspore and its environment.
This study has a reference value for future studies on B. tectorum. The result was published in Journal of Arid Land on September 2013, 5(3): 310-323.
Bromus tectorum L. (Cheatgrass) is an annual grass native to Central Asia and currently found in other parts of the world, including Europe and North America. B. tectorum has become one of the most problematic invasive species in North America since its introduction in the late 19th century.
B. tectorum produces diaspores and forms a seed bank in the soil, and in drier habitats, the soil seed bank will sustain for a long time. In addition, diaspore size significantly influences seedling survival. Diaspores are among the most important reproductive organs of seed plants and are produced during an important stage of the plant life cycle. Diaspores act as a link between different generations; this role of the diaspore has vital significance on individual reproduction and population extension. Hence, diaspores under selection for studying have an important implication.
This study compares differences in seed morphology for B. tectorum collected from the United States, Kazakhstan, and Xinjiang of China. The following indices of B. tectorum diaspores were analyzed: size, thickness of covering layers, and micromorphological characteristics of the base, middle and transition area of diaspores as well as of the awn. Micromorphology of the lemma and the cross-section of the diaspore were observed by scanning electron microscopy.
Results showed that thickness of the lemma and the palea of diaspores from B. tectorum-infested grasslands in the United States were reduced (P<0.05), likely because of environmental influences. This reduction facilitated the germination of diaspores and lowered the resistance of B. tectorum to adverse environmental conditions. The length of the awn also increased significantly (P<0.05), which helped in dispersal and anchoring of diaspores. Therefore, B. tectorum adapted ecologically to its new environment in the United States by strengthening its establishment ability. However, the defense capability of B. tectorum decreased.
These results fit the evolution of increased competitive ability hypothesis (EICA) of invasive species. Analysis of various cells on the lemma revealed that prickle densities and collapsed, long epidermal cells were easily influenced by environmental factors such as temperature and moisture because of the physiologic function of these structures on silicon accumulation. However, the form and the position of silica cells, which were not greatly influenced by environmental factors, might be genetically controlled. Studying these structures at the microscopic level helps define the relationship between the diaspore and its environment.
This study has a reference value for future studies on B. tectorum. The result was published in Journal of Arid Land on September 2013, 5(3): 310-323.