Abstract:
The goal of this dissertation was to improve our understanding of the
physiology and life-history of invasive plants and of the mechanisms underlying
life-history trade-offs. I compared invasive and noninvasive species of Rubus
(blackberry) that grow together in the Pacific Northwest. Three hypotheses were
investigated: (1) Invasive Rubus have higher photosynthetic capacity and lower
leaf-level resource costs of photosynthesis than native, noninvasive species; (2) The
physiological effects of reproduction on foliage result in higher reproductive effort
for noninvasive Rubus than for an invasive species, in spite of the greater number
and size of fruit produced by the invasive species; and (3) Reproduction produces
greater trade-offs to growth for noninvasive Rubus because of its higher
reproductive effort, and these trade-offs affect the population demographics of these
species.
I found that two invasive species, R. discolor and R. laciniatus, had higher
photosynthetic capacities and maintained these rates for a longer portion of the year than two noninvasive species, R. ursinus and R. leucodermis. Furthermore, the two
invasive species had higher rates of photosynthesis per unit resource investment,
such as carbon, nitrogen, and water, than the noninvasive Rubus. I found that these
photosynthetic characteristics could be used to distinguish between the noninvasive
and invasive species using discriminant analysis.
I compared reproductive effort for one of the invasive, R. discolor, and one
of the noninvasive, R. ursinus, species. I found that, although the invasive Rubus
allocated more resources directly to reproduction than the noninvasive species, it
had lower reproductive effort because it did not have the significant decline in leaf
nitrogen and photosynthetic capacity and significant increase in mid-day water
stress that were associated with reproduction in the noninvasive species.
I also observed that sexual reproduction in the noninvasive species was
associated with trade-offs to growth both within and between generations, but these
were not observed in the invasive species. These trade-offs in the noninvasive
species resulted in an almost complete dependence on clonal growth rather than
sexual reproduction for population growth. The invasive Rubus relied on sexual
reproduction for population growth relatively more than the noninvasive species
and, therefore, reproductive effort influenced the demographics of these species.
