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Conservation Genetics
Plants

Samples of genetics and genomics research from the USGS Ecosystems Mission Area about the conservation genetics of plants.

Multilocus patterns of nucleotide polymorphism and demographic change in Taxodium distichum in the Lower Mississippi Alluvial Valley
Photo:bald cypress (Taxodium distichum). Photo credit: Beth Middleton, USGS.
Photo:bald cypress (Taxodium distichum). Photo credit: Beth Middleton, USGS.

The National Wildlife Research Center is a part of a joint project along with Kyushu University (Fukuoka Japan) and the Forest and Forestry Products Institute (Tsukuba Japan) to determine genetic variation in bald cypress (Taxodium distichum). Some of the research looks at genetic patterns across the range of Taxodium distichum in North America and Cryptomeria japonica in Japan. The genetic patterns of T. distichum indicate that the species has expanded rapidly after the last glacial epoch, and that the regional variation between populations is not all that great. From a climate change perspective, the genetic studies indicate that the responses of individuals might be fairly similar across the Mississippi River Alluvial Valley, because the populations are not very different from one another genetically. Another segment of this research suggests that the populations from Florida and the Mississippi River Alluvial Valley differ from each other indicating that the current day populations in these two geographic locations may have originated from different glacial refugia. For more information, contact Beth Middleton at the USGS National Wetlands Research Center.

Link to abstract: Multilocus patterns of nucleotide polymorphism and demographic change in Taxodium distichum (Cupressaceae) in the lower Mississippi River alluvial valley

 

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Soil warming alters seed-bank responses across the geographic range of Taxodium distichum swamps
Photo:Cypress swamp (Taxodium distichum). Photo credit: Beth Middleton, USGS.
Photo:Cypress swamp (Taxodium distichum). Photo credit: Beth Middleton, USGS.

Climate change may have important effects on species distribution in the future, but some species may have more flexibility than others to respond to changing environments. Heating studies of seed germination were conducted from seed banks collected across the geographic range of Taxodium distichum swamps. Based on this work, researchers found that a few species have populations whose variation across these ranges changes in response to temperature. These species have individuals that may be able to respond more flexibility to increasing temperatures as climate changes (e.g., Cephalanthus occidentalis, Saururus cernuus and Polygonum pensylvanicum). These species will be the subject of future genetic studies with molecular colleagues. For more information, contact: Beth Middleton and Karen McKee, at the USGS National Wetlands Research Center.

Link to Abstract: Soil warming alters seed-bank responses across the geographic range of freshwater Taxodium distichum (Cupressaceae) swamps.

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American Ginseng (Panax quinquefolius L.)
John A. Young sampling American ginseng for genetic analysis. Photo credit: Mike Eackles, USGS Leetown Science Center
John A. Young sampling American ginseng for genetic analysis. Photo credit: Mike Eackles, USGS Leetown Science Center

American ginseng (Panax quinquefolius L.) is a perennial herb that is harvested for the purported medicinal qualities of its root.  Harvest and export of ginseng roots to Asia has long been a source of supplementary income for people living in the Appalachian Mountains, but recent increases in the market value of American ginseng roots have intensified legal (and illegal) harvest pressure.  Concerns of possible over-harvest led to listing of American ginseng in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).  Under CITES, the U.S. Fish and Wildlife Service (USFWS), Division of Scientific Authority (DSA) must determine whether the export of American ginseng will be detrimental to the survival of the species, and whether wild-harvest is sustainable. American ginseng is also cultivated in woodlands, but it is unclear what effect this “wild-simulated” ginseng is having on native populations.

Little quantitative demographic data exists for American ginseng, and little is known about its population characteristics in relation to harvest levels.  Scientists at the USGS Leetown Science Center have developed geospatial models that predict the distribution of habitats suitable for American ginseng, and these models were used to provide the DSA with estimates of population status and harvest pressure in the core of its range.  Currently, we are expanding our studies to be nearly inclusive of the entire range of American ginseng within the U.S., and we are collecting plant material to determine the genetic variability of the species.  We are developing microsatellite DNA markers to identify and map the genetic variation of American ginseng within and among sites.  The demographic, habitat, and genetic data provided by this project should greatly improve the information available to USFWS for determining the status and protection needs of this species.

For more information, contact John A. Young, Leetown Science Center.

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Coastal Freshwater Forested Wetlands
Coastal swamp forest in southeastern Louisiana. Photo credit: William H. Conner, Clemson University

Coastal swamp forest in southeastern Louisiana.  Photo credit: William H. Conner, Clemson University

Coastal freshwater forested wetlands are under increasing stress associated with sea-level rise and salinization along the Gulf and south Atlantic Coasts.  For nearly two decades, forest ecologists at the USGS National Wetlands Research Center in Lafayette, Louisiana have studied the eco-physiological and morphological responses of genetically distinct tree populations from these areas to different salinity and flood regimes.  The goal of this research is to identify “improved” genotypes that can in turn be used for large-scale coastal swamp forest restoration efforts on marginal sites.  Research to date has targeted baldcypress (Taxodium distichum) because of its longer term survival on salt-impacted sites as well as its broad tolerance to flooding.  Studies have revealed strong intraspecific variation in tolerance to low salinity levels (approaching 4 ppt) among seedlings propagated from different coastal populations.  However, persistent exposure to higher salinities eventually results in mortality for all genotypes.  Recent research has suggested that natural selection may favor broad in lieu of narrow tolerances in baldcypress, thereby precluding strong adaptation to specific flood regimes.  The consequences of such a broadly adaptive strategy for the future of salt tolerance improvement are unknown, but will continue to be a focus of this research.

For more information, contact Ken W. Krauss, National Wetlands Research Center.

Publications:

  • Krauss, K.W., T.W. Doyle, and R.J. Howard. 2009. Is there evidence of adaptation to tidal flooding in saplings of baldcypress subjected to different salinity regimes? Environmental and Experimental Botany 67: 118-126.
  • Krauss, K.W., J.L. Chambers, and D. Creech. 2007. Selection for salt tolerance in tidal freshwater swamp species: advances using baldcypress as a model for restoration. Pages 385-410 in W.H. Conner, T.W. Doyle, K.W. Krauss (eds.), Ecology of Tidal Freshwater Forested Wetlands of the Southeastern United States. Springer. 505 p.
  • Krauss, K.W., J.L. Chambers, J.A. Allen, D.M. Soileau, Jr., and A.S. DeBosier. 2000. Growth and nutrition of baldcypress families planted under varying salinity regimes in Louisiana, USA. Journal of Coastal Research 16: 153-163.
  • Krauss, K.W., J.L. Chambers, J.A. Allen, B. Luse, and A.S. DeBosier. 1999. Root and shoot responses of Taxodium distichum seedlings subjected to saline flooding. Environmental and Experimental Botany 41: 15-23.
  • Krauss, K.W., J.L. Chambers, and J.A. Allen. 1998. Salinity effects and differential germination of several half-sib families of baldcypress from different seed sources. New Forests 15: 53-68.
  • Allen, J.A., W.H. Conner, R.A. Goyer, J.L. Chambers, and K.W. Krauss. 1998. Chapter 4: Freshwater forested wetlands and global climate change. Pages 33-44 in G.R. Guntenspergen and B.A Vairin (eds.), Vulnerability of coastal wetlands in the Southeastern United States: climate change research results, 1992-97. U.S. Geological Survey, Biological Resources Division Biological Science Report USGS/BRD/BSR-1998-0002. 101 p.
  • Allen, J.A., J.L. Chambers, and S.R. Pezeshki. 1997. Effects of salinity on baldcypress seedlings: physiological responses and their relation to salinity tolerance. Wetlands 17: 310-320.
  • Allen JA, S.R. Pezeshki, and J.L. Chambers. 1996. Interaction of flooding and salinity stress on baldcypress (Taxodium distichum). Tree Physiology 16: 307-313
  • Allen, J.A., J.L. Chambers, and M. Stine. 1994. Prospects for increasing the salt tolerance of forest trees: a review. Tree Physiology 14: 843-853
  • Allen, J.A., J.L. Chambers, and D. McKinney. 1994. Intraspecific variation in the response of Taxodium distichum seedlings to salinity. Forest Ecology and Management 70: 203-214

See also Conservation Genetics - Landscapes >>

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Featured Publication

Bald cypress. Photo credit: Bill Lea, USDAA recent article from the National Wetlands Research Center examines how plant populations may adapt to environmental conditions over time by developing genetically based morphological or physiological characteristics. Using baldcypress (Taxodium distichum (L.) L.C. Rich) from the southeastern United States, findings suggest that adaptations of coastal baldcypress to broad (rather than narrow) environmental conditions may promote ecophysiological and growth enhancements under a range of global-change-induced stressors, perhaps reflecting a natural resilience to environmental change while precluding adaptations for specific flood regimes.

See the related research summary Coastal Freshwater Forested Wetlands.

For more information contact Ken W. Krauss, National Wetlands Research Center.

Krauss, K.W., Doyle, T.W., and Howard, R.J. Is there evidence of adaptation to tidal flooding in saplings of baldcypress subjected to different salinity regimes? Environmental and Experimental Botany, Volume 67, Issue 1, November 2009, Pages 118-126. doi:10.1016/j.envexpbot.2009.05.005 
Online abstract >>

This research was funded by the Global Change Science of the Terrestrial, Freshwater, and Marine Ecosystems Program.

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