Doctor of Philosophy / Department of Biology / David C. Hartnett / In perennial grasslands, the belowground population of meristems (the bud bank) plays a
fundamental role in local plant population structure and dynamics. I tested the “meristem
limitation hypothesis” prediction that bud banks increase along an increasing
precipitation/productivity gradient in North American grasslands. I sampled bud populations
quarterly at six sites across a 1,100 km gradient in central North America. Bud banks increased
with average annual precipitation, which explained 80% of variability in bud banks among sites.
Seasonal changes in grass bud banks were surprisingly similar across a 2.5-fold range in
precipitation and a 4-fold range of aboveground net primary productivity (ANPP). Secondly, I
tested the hypothesis that tallgrass prairie plants respond to increases in a limiting resource
(nitrogen) through demographic effects on the bud bank. I parameterized matrix models for
individual genets, considering each genet as a population of plant parts (buds and stems).
Nitrogen addition significantly impacted bud bank demography of both Sporobolus heterolepis
and Koeleria macrantha. In 2005, emergence from the bud bank and growth rates (λ) of the tiller
population were significantly higher in S. heterolepis genets that received nitrogen. In contrast, nitrogen addition decreased λ in K. macrantha. Both prospective and retrospective analyses indicated that bud bank dynamics are the key demographic processes driving genet responses to nutrient availability. Lastly, I tested the hypothesis that the effects of fire and grazing on plant species composition and ANPP are mediated principally through demographic effects on bud
banks. I found that plants respond to fire and grazing with altered rates of belowground bud
natality, bud emergence, and both short-term (fire cycle) and long-term changes in bud density.
The size of the bud bank is an excellent predictor of long-term ANPP, supporting my hypothesis
that ANPP is strongly regulated by belowground demographic processes. Meristem limitation
due to water or nutrient availability or management practices such as fire and grazing may
constrain grassland responses to inter-annual changes in resource availability. An important
consequence is that grasslands with a large bud bank may be the most responsive to future
climatic change or other phenomena such as nutrient enrichment, and may be most resistant to
exotic species invasions.
| Identifer | oai:union.ndltd.org:KSU/oai:krex.k-state.edu:2097/312 |
| Date | January 1900 |
| Creators | Dalgleish, Harmony J. |
| Publisher | Kansas State University |
| Source Sets | K-State Research Exchange |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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