Arredondo and Johnson studied the effects of simulated grazing at different intensities (0, 50, and 70% utilization) and frequencies (single or repeated defoliation) on root architecture and morphology, of three grassland species that are common in the western United States, bluebunch wheatgrass (Pseudoroegneria spicata), crested wheatgrass (Agropyron desertorum), and cheatgrass (Bromus tectorum). Specific root length, which can represent a plant's ability to utilize soil resources, was maintained in cheatgrass plants throughout the study with and without clipping. In contrast, specific root length decreased in the absence of grazing and increased in the presence of grazing in crested wheatgrass and bluebunch wheatgrass. Bluebunch wheatgrass and crested wheatgrass plant root response to defoliation varied greatly from cheatgrass, which increased link length and decreased interbranch distance and root diameter. Bluebunch wheatgrass decreased link length and increased interbranch distance and root diameter in response to grazing. Although the root system growth and response to grazing differed among these three plant species, the underlying strategy of all three plant species was to increase the acquisition of soil resources for plant growth.
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