Browsing by Author "William Hoffmann, Committee Member"

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Assessing the Reliability of Hydrologic Characterizations of Four Wetland Plant Communities
(2008-05-14) Conk, Carlin Elizabeth; William Hoffmann, Committee Member; Stephen Broome, Committee Co-Chair; Michael Vepraskas, Committee Co-Chair
Previous field work characterized the wetness requirements of four plant communities by modeling their hydrologic regimes in three reference wetlands and correlating the results. The objectives of this work were to: 1) determine whether the modeled predictions were accurate by growing four tree species that represented different plant communities under the modeled hydrologies in the greenhouse, and 2) determine how different tree species adapt to saturated soil conditions. Bald cypress (Taxodium distichum), sweet bay (Magnolia virginiana), pond pine (Pinus serotina), and swamp chestnut oak (Quercus michauxii) were grown in greenhouse experiments under three hydrologic regimes: i) ponded for 100 d, ii) ponded for 15 d, and iii) unsaturated. Loamy sand and sapric materials from a restored Carolina Bay were the substrate materials used to represent mineral and organic soils. Bald cypress (representing Non-riverine Swamp Forest) adapted well to 100 d of ponding by producing lateral roots near the surface, aerenchyma tissue in roots and stem, and increasing P uptake. In organic soils ponded for 100 d, bald cypress had significantly greater height, diameter, and total biomass than all other tree species. Sweet bay (representing Bay Forest) adapted well to 100 d of ponding by producing adventitious roots on the submerged portion of the stem. Pond pine (representing Pond Pine Woodland) was intolerant to 100 d of ponded conditions and 75% of the seedlings died in the ponded experiments. Swamp chestnut oak (representing Non-riverine Wet Hardwood Forest) was intolerant to ponding and all seedlings died in ponded treatments. A rhizotron study was conducted to further observe and quantify biological, morphological, and physiological changes in two wetland tree species with differing tolerances to saturated conditions. Bald cypress and swamp chestnut oak seedlings were grown under ponded and unponded conditions for 106 d in rhizotrons containing the same soils used in the container study. Within 2 wk of ponding, bald cypress (BC) seedlings in both organic and mineral soils began to produce lateral roots within the top 36 cm of soil. The swamp chestnut oak (SCO) seedlings subjected to ponding did not produce many new roots, and root death was observed within 4 wk of flooding. Scanning electron microscopy images of basal stems and roots of BC subjected to saturation showed substantial development of aerenchyma, which may have aided in the overall tolerance of BC to ponded conditions. This study showed BC seedlings developed numerous adaptations to saturated conditions, which allowed them to grow in wet organic soils of the Coastal Plain. Results from the container and rhizotron experiments showed that modeling of the long-term hydrology of natural communities was accurate in predicting the preferred wetness requirements of representative trees in three of the four plant communities evaluated.
Genetic Variation in Water Relations, Physiology, Biochemistry and Biomass Partitioning in Loblolly Pine.
(2010-05-04) Aspinwall, Michael Joseph; Steven McKeand, Committee Chair; John King, Committee Chair; William Hoffmann, Committee Member; Fikret Isik, Committee Member; Jean-Christophe Domec, Committee Member
The Population Ecology of Ant-dispersed Plants in Space and Time.
(2010-07-27) Canner, Judith; Kevin Gross, Committee Chair; Robert Dunn, Committee Chair; William Hoffmann, Committee Member; MORRIS, WILLIAM (DUKE), Committee Member