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The effect of timing of growing season drought on flowering of Andropogon gerardii




Dietrich, John David, author
Smith, Melinda D., advisor
Knapp, Alan K., committee member
Ocheltree, Troy W., committee member

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Timing of precipitation is equally important as amount for determining ecosystem function, especially aboveground net primary productivity (ANPP), in a variety of ecosystems. The particular precipitation period(s) of greatest importance varies between ecosystems. In tallgrass prairie of the central US, the relative importance of different precipitation periods is dictated by the phenology of the dominant C4 grasses, in particular Andropogon gerardii which can contribute >80% to ANPP in this ecosystem. It is predicted that precipitation periods with the greatest impact on the highly variable flowering rates of A. gerardii are likely to be particularly important for determining ANPP, as flowering individuals are much larger (>2-fold) than non-flowering individuals. The potential for flowering may be affected by precipitation at different times via different mechanisms (e.g. carbon gain via rapid growth early in the growing season vs. direct effects on stalk elongation later in the growing season). In order to test the differential effects of precipitation timing, rainfall deficits (100% exclusion) at different periods of the growing season were imposed on native tallgrass prairie in Kansas, USA. Contrary to expectations, the most sensitive period in terms of flowering for A. gerardii did not coincide with the highest potential photosynthetic rates early in the growing season. Rather the most sensitive period was mid to late summer immediately preceding, and concurrent with, the initiation of flowering stalks. Growth rate, leaf water potential and carbon assimilation of A. gerardii were all most sensitive to drought late in the growing season, suggesting that growth regulation in response to plant water status, not current year’s carbon accumulation is the critical factor determining flowering responses to precipitation or lack thereof. Flowering, in addition to influencing ANPP, controls rates of sexual reproduction which in turn limit adaptation and migration, and thus understanding how flowering will be influenced by a changing climate is critical for predicting plant community and ecosystem responses in tallgrass prairie. My study suggests that increased frequency of growing season droughts forecast with climate change could result in reduced ANPP and reproductive success of the dominant grasses in the tallgrass prairie ecosystem.


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precipitation timing
tallgrass prairie


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