Document Type

Thesis - Open Access

Award Date

2018

Degree Name

Master of Science (MS)

Department / School

Natural Resource Management

First Advisor

Lan Xu

Abstract

Perennial grasslands are remarkably resilient to severe natural and anthropogenic disturbances. Such resiliency largely depends on successful tiller recruitment and establishment from belowground bud banks. In the northern Great Plains, introduced perennial smooth bromegrass (Bromus inermis) has been rapidly invading and transforming larger tracts of native prairies by replacing native perennial species, such as western wheatgrass (Pascopyrum smithii), reducing biodiversity and quality of habitats, and increasing vulnerability of grasslands to other environmental disturbances. In this study, we evaluated the response of belowground bud production, tiller and rhizome recruitment, and plant establishment between the native P. smithii and the non-native B. inermis to altered precipitation frequency, clipping, and competition with two different controlled greenhouse experiments over two growing seasons. In the first experiment, the treatments consisted of combinations of three precipitation frequencies (every 2d, 8d, and 16d) representing high, medium, and low, two levels of clipping (clipping vs. no-clipping), and two species with 40 replicates for each treatment. One single-leaf seedling of each species was transplanted into individual potting-soil filled pots in mid-June. We initiated precipitation frequency treatments and applied a clipping treatment two weeks after transplanting. Plants were harvested 20 weeks after the treatments had been initiated. The number of tillers and rhizomes based on generation, number of tillers based on location (crown vs. rhizome), and rhizome length were recorded. Three randomly sub-sampled tillers and rhizomes from each generation were dissected to record the number of buds and propagule development. We found B. inermis significantly decreased their number of tillers, rhizomes, rhizome length, and live propagules at the low precipitation frequency, but increased propagule development at medium precipitation frequency. However, P. smithii significantly increased the traits described above under medium precipitation frequency, except for the number of tillers and propagule development, which were not affected at medium and low precipitation frequency. The clipping significantly reduced tiller production for both species and the number of rhizomes for B. inermis. The results indicate that non-native B. inermis may be more susceptible to the altered precipitation frequency and clipping compared to native P. smithii. Native P. smithii may be able to resist the soil moisture variability and clipping effects mediated via the belowground bud banks. The second competition experiment consisted of five treatments including single B. smithii, single P. smithii, pairwise monoculture of B. inermis, pairwise monoculture of P. smithii, and pairwise mixed-culture of B. inermis and P. smithii with 30 replicates for each treatment under every 2d precipitation frequency regime. Double-leaf seedlings of each species were transplanted into individual potting soil-filled pots based on designated treatments. Plants were harvested 12 weeks after the treatments had been initiated. The data collection followed the same protocol as the first experiment. In addition, biomass and relative interaction index (RII) were calculated to determine intra- and inter-specific competition between P. smithii and B. inermis. We found that the presence of B. inermis as a neighbor significantly decreased the number of live propagules, tillers, and aboveground biomass of the native P. smithii. However, the presence of P. smithii as a neighbor significantly increased the number of live propagules and had significantly less negative effect on tiller production and aboveground biomass of B. inermis. Also, investment in dual phalanx and guerilla growth by B. inermis while competing with P. smithii indicates possible phenotypic plasticity trait. All results demonstrated a strong competitive ability of the non-native B. inermis against P. smithii during the establishment phase when environmental conditions are favorable (i.e. lack of water stress and grazing). Overall, we can conclude that species establishment and interaction between these two key perennial grasses in northern mixed-grass prairies is environmentally dependent and species specific. The outcomes are mediated by the response of the belowground bud bank. The findings from this study can help us to better understanding the mechanisms of bud banks in maintaining tiller population, regulating vegetation dynamics, productivity, and response to climate change in the context of grazing practices and invasion by nonnative perennial grasses. They could form the basis for a long-term effective grassland management plan.

Library of Congress Subject Headings

Smooth brome.
Western wheatgrass.
Grassland ecology.
Resilience (Ecology)

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

172

Publisher

South Dakota State University

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Rights Statement

In Copyright