Plant form is a compromise between resource gathering, reproduction and
the tolerance to physical demands of the abiotic and biotic environment. In
an agricultural field in addition to the natural factors causing stress, humans
also introduce physical and mechanical stresses, and chemical pesticides
into the environment. Many of these factors are hazardous, since they
represent stresses to which plants are unable to develop defense
mechanisms. However, weeds have persisted in the agricultural
environment despite the efforts to eradicate them. They have adapted to
environmental changes such as crop rotation and have developed tolerance
to stressors like pesticides in very short periods of times (less than 10
years), much less time than normally expected for evolutionary responses
to occur. Perhaps a key to why weeds persist in stress-dominated habitats
is the way they compromise between yield and survival. The mechanisms
that explain which process is relevant in the control of seed production or
seedling growth relate to the ecophysiology of the individual plants.
However, trade-offs between plants physiological functions will have
implications at both population and community levels.
Climate change, air pollution and water scarcity are examples of
environmental stresses that particularly affect agriculture. Herbicides are a
major technological tool for agriculture and are responsible, at least in part,
for significant increases in crop production during the last quarter of the
century. The research presented in this dissertation was developed to
understand the extent that individual responses to multiple environmental
stresses can be extrapolated to population-level responses in an annual
weed species.
The specific objectives were to assess (1) the impact of three
anthropogenic stresses (herbicide, UVB light and ozone) and their
interactions on individual Italian ryegrass ontogeny and reproduction and
(2) the potential evolutionary effect of these stresses and combinations on
changes in population size and structure over time.
Plants were capable of growth and reproductive compensation under
the studied stresses. Stress factors with similar biochemical
mechanisms had different effects at the individual plant and population
levels of organization. Compensation occurred at all levels of
organization: as individuals modifying growth and allocation to different
organs and as populations modifying birth, and death rates and density
dependent responses. The ability to compensate sometimes decreased
with the number of stress factors (e.g. herbicide and UVB). In other
cases, compensation ability increased with the number of stress factors
(e.g. ozone and herbicide). / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30900 |
| Date | 15 March 2004 |
| Creators | Martinez-Ghersa, Maria Alejandra |
| Contributors | Radosevich, Steven R. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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