BSC 226/L General Botany
BSC 432/532 Economic Botany
BSC 435/535 Plant Ecology
My research interests focus on plant community responses to stresses, either natural or anthropogenic, and the physiological basis by which these responses are manifested. Specifically, my current research includes the following:
- Response of southeastern ecosystems to global climate change
Global atmospheric CO2 concentrations are projected to double by the end of this century. Although the effects of CO2 on global temperature receive much attention, the direct effects of changing CO2 concentrations on photosynthesis play an equally important role in determining ecosystem response to anthropogenic emissions. Carbon dioxide is the molecular nexus between the biosphere and the atmosphere (and thus the universe). The conversion of CO2 into organic sugars utilizing light and chemical energies represents the ultimate source of input of metabolic energy into living organisms. Politically, tracking CO2 and limiting emissions is at the top of the environmental agendas of every developed nation in the world. Until global emissions can be significantly lowered, carbon sequestration strategies and trading schemes represent the best way to mitigate carbon emissions.
Our ability to predict the consequences of climate change is predicated on our understanding of controls of energy and material flows through ecosystems. Currently, the most significant gap in that understanding lies belowground. Unfortunately, the opaque nature of soil has made in situ observation of belowground ecology difficult. I use Minirhizotron cameras to visualize growth of individual roots through time and thus overcome some past problems. Current data indicate that root growth is increased by CO2-enrichment, but this enhancement occurs at different soil depths depending on edaphic characteristics and community composition. For instance, CO2 effects were only manifested at shallow depths in a 20 yr old loblolly pine forest (Duke University FACE), while a model regenerating longleaf pine forest (USDA-ARS/Auburn University OTC) realized the greatest belowground CO2 benefit at greater soil depths.
Although CO2 enrichment generally enhances photosynthesis and growth, species differing in physiology (e.g. C4 vs. C3), growth form (e.g. tree vs. forb), phenology (e.g. annual vs. perennial; deciduous vs. evergreen), and symbiotic relationships (e.g. N-fixers vs. non-N-fixers) differ greatly in their long-term response to elevated CO2. These differences can alter competitive relationships in plant communities, and over time can alter community structure and function. Indeed, data from our longleaf pine experiment show that competitive ability for limiting resources, i.e. light and soil moisture, can supersede physiological advantages for carbon fixation.
All of the above responses to rising CO2 impact subsequent fluxes of energy through food webs within forest communities. I am examining the effects of CO2-enriched forest litter on the diversity of soil fauna within several southeastern ecosystems: a pine forest (Duke University FACE), a hardwood forest (Oak Ridge National Laboratory FACE) and an agroecosystem (USDA-ARS/Auburn University OTC). Preliminary data indicate community composition is altered in CO2 -enriched plots at Duke Forest.
Colloborators: Hugo Rogers, Seth Pritchard, Steve Prior, Brett Runion, Rich Norby
- Impacts of forestry management techniques on floral diversity
Maintaining biodiversity while increasing production is a main thrust in forest management strategies. Understanding how forest management techniques affect biodiversity enables timber companies to maximize yield while minimizing long-term environmental impacts. Most of our data show that site preparation techniques and pine release treatments generally do not affect long-term diversity and species richness in pine plantations.
Diversity and species richness are not static, but in fact change with stand age. A recent chronosequence stand study in Tuskegee National Forest shows that diversity and species richness peak early (0-20 yr old), dip significantly in "pole"- and "saw-timber"-aged longleaf pine stands (20-70 yr old), and then rise again in mature stands (>80 yr old).
Collaborators: James Miller, Robert Boyd
- The ecology of serpentine flora
Pollution by heavy metals is an important environmental concern. The use of metal- hyperaccumulating plants to phytoremediate mine spoils is an emerging industry. These plants sequester extraordinary amounts of metals in their tissues. I am interested in the ecological significance of this unique trait, particularly the effects of metal hyperaccumulation on plant/herbivore interactions within serpentine communities. Current and recent research sites include serpentine areas in California, South Africa, and New Caledonia. Planned research sites include serpentine areas in France, Cuba, and Costa Rica.
Collaborators: Robert Boyd, Michael Wall, Kevin Balkwill
Allan E. Strand, Seth G. Pritchard, M. Luke McCormack, Michael A. Davis, Ram Oren. 2008. Irreconcilable differences: Fine-root life spans and soil carbon persistence. Science, 319:456-458.
Pritchard, Seth G., Allen E. Strand, M. Luke McCormack, Micheal A. Davis, Adrien C. Finzi, Robert B. Jackson, Roser Matamala, Hugo H. Rogers, and Ram Oren. 2008. Fine root dynamics in a loblolly pine forest are influenced by free-air-CO2-enrichment: a six-year-minirhizotron study. Global Change Biology, 14:588-602.
Boyd, R.S., Micheal A. Davis, Michael A. Wall, and Kevin Balkwill. 2007. Host-herbivore studies of Stenoscepa sp. (Orthoptera: Pyrgomorphidae), a high-Ni herbivore of the South African Ni hyperaccumulator Berkheya coddii (Asteraceae). Insect Science, 14:133-143.
G. Brett Runion, Micheal A. Davis, Seth G. Pritchard, Stephen A. Prior, H, Allen Torbert, Hugo H. Rogers, and Roland R. Dute. 2006. Effects of elevated atmospheric CO2 on biomass and carbon accumulation in a model regenerating longleaf pine ecosystem. Journal of Environmental
McCarthy, Heather R., Ram Oren, Hyun-Seok Kim, Kurt H. Johnsen, Chris Maier, Seth G. Pritchard, and Micheal A. Davis. 2006. Interaction of ice storms and management practices on current carbon sequestration in forests with potential mitigation under future CO2 atmosphere. J. Geophysical Research - Atmospheres, 111, D15103.
Edward M. Jhee, Robert S. Boyd, Mickey D. Eubanks, and Micheal A. Davis. 2006. Nickel hyperaccumulation by Streptanthus polygaloides protects against the folivore Plutella xylostella (Lepidoptera: Plutellidae). Plant Ecology, 183:91-104.
Pritchard, Seth G., Stephen A. Prior, Hugo H. Rogers, Micheal A. Davis, G. Brett Runion, and Thomas W. Popham. 2006. Effects of elevated CO2 on root dynamics of sorghum grown under sustainable and conventional agricultural management systems. Agriculture, Ecosystems, and Environment, 113:175-183.
Saxon, Milam E., Micheal A. Davis, Seth G. Pritchard, G. Brett Runion, Stephen A. Prior, Hank S. Steltzer, Hugo H. Rogers, Roland R. Dute. 2004. Influence of elevated CO2 , nitrogen, and Pinus elliottii genotype on performance of the redheaded pine sawfly Neodiprion lecontei. Canadian Journal of Forest Science, 1007-1017.
Davis, Micheal A., Seth G. Pritchard, Robert J. Mitchell, Stephen A. Prior, Hugo H. Rogers, & G. Brett Runion. 2002. Elevated atmospheric CO2 affects structure of a model regenerating longleaf pine community. Journal of Ecology, 90: 130-140, cover photo.
Boyd, Robert S., Micheal A. Davis, Michael A. Wall, & Kevin Balkwill. 2002. Nickel defends the South African hyperaccumulator Senecio coronatus (Asteraceae) against Helix aspersa (Mollusca: Pulmonidae). Chemoecology, 12: 91-97.
Davis, Micheal A., John F. Murphy, & Robert S. Boyd. 2001. Nickel increases susceptibility of the Ni hyperaccumulator, Streptanthus polygaloides, to Turnip mosaic virus. Journal of Environmental Quality, 30: 85-90, cover photo.
Pritchard, Seth G., Micheal A. Davis, Robert J. Mitchell, Stephen A. Prior, Debbie L. Boykin, Hugo H. Rogers, & G. Brett Runion. 2001. Root dynamics in a model regenerating longleaf pine ecosystem are affected by CO2 enrichment. Environmental and Experimental Botany, 46: 55-69.