Environmental stresses such as extremes in soil water availability prevent many attractive woody plants from surviving in managed landscapes (Kjelgren et al., 2000). As such, there is an increasing demand in the nursery industry for aesthetic, yet stress-resistant, trees and shrubs. Because of the high costs of propagation, cultivation, transplantation, and establishment, trees and shrubs constitute a substantial financial investment by nurseries (Campbell et al., 2001; Harris et al., 1999). Efforts to ensure plant survival, and thus to minimize economic losses, are readily welcomed by the nursery industry.
It is generally assumed that a species’ native habitat and climate are reliable indicators of the prospective cultivated range of a species. Past research, however, has shown that some novel ornamental woody species have the ability to withstand stresses not normally experienced in their native ranges (Schrader et al., 2005; Stewart and Graves, 2004).
We decided to evaluate the relative vigor, as indicated by net photosynthesis and plant growth, of three taxa that grow wild in relatively small areas in the United States and may merit use in managed landscapes: Calycanthus occidentalis Hook. & Arn. (western sweetshrub), Fraxinus anomala Torr. ex S. Watson (single-leaf ash), and Pinckneya pubens Michx (fevertree). Calycanthus occidentalis, a western congener of the widely cultivated Calycanthus floridus L., is a multistemmed shrub or small tree native to primarily the Sierra Nevada in north–central California, but also is found in Oregon and Washington (Hickman, 1993). It is a common shrub of moist habitats, including stream borders and shaded canyons (Grant, 1950; Hickman, 1993; Shevock et al., 1992). Similar to C. occidentalis, F. anomala is a multistemmed shrub or small tree but is found along rimrock or drainages in pinyon-juniper forests within Arizona, California, Colorado, New Mexico, Nevada, and Utah (Welsh, 1987). Unlike many of its congeners, F. anomala generally has monofoliate leaves, but frequently has trifoliate leaves as well (J. R. Stewart, personal observation). Pinckneya pubens is also a multistemmed shrub or small tree with large distinctive flowers that is found in Georgia, northern Florida, and South Carolina (Delprete, 1996). The taxon grows in swamp forests, edges of boggy areas, and other poorly drained soils (Delprete, 1996). Because marshy areas are drained for agriculture and urban development, P. pubens is losing its natural habitat (J. Sharma, personal communication). The respective semiarid and marshy habitats of F. anomala and P. pubens imply that both species may be tolerant of at least some extremes in soil moisture found in horticultural landscapes.
Our objective was to characterize, under greenhouse conditions, the effect of soil water availability on leaf gas exchange and carbon-allocation patterns in potted plants of each species. Measuring these physiological variables has been shown to be an effective method of gauging the potential landscape performance of woody species (Balok and St. Hilaire, 2002; Bsoul et al., 2006; Schrader et al., 2005; Stewart and Graves, 2004).
Balok, C.A. & St. Hilaire, R. 2002 Drought responses among seven southwestern landscape tree taxa J. Amer. Soc. Hort. Sci. 127 211 218
Bsoul, E., St. Hilaire, R. & VanLeeuwen, D.M. 2006 Bigtooth maples exposed to asynchronous cyclic irrigation show provenance differences in drought adaptation mechanisms J. Amer. Soc. Hort. Sci. 131 459 468
Campbell, G.E., Brazee, R.J., Endress, A.E., Voigt, T.B., Warnock, D.F. & Hall, J.L. 2001 The Illinois green industry: Economic impact, structure, characteristics University of Illinois at Urbana–Champaign
Croker, J., Witte, W. & Auge, R. 1998 Stomatal sensitivity of six temperate, deciduous tree species to non-hydraulic root-to-shoot signalling of partial soil drying J. Expt. Bot. 49 761 774
Delprete, P.G. 1996 Systematics, typification, distribution, and reproductive biology of Pinckneya bracteata (Rubiaceae) Plant Syst. Evol. 201 243 261
Dirr, M.A. 1998 Manual of woody landscape plants: Their identification, ornamental characteristics, culture, propagation, and uses Stipes Publ Champaign, IL
Dougherty, P.M., Teskey, R.O., Phelps, J.E. & Hinckley, T.M. 1979 Net photosynthesis and early growth trends of a dominant white oak (Quercus alba L.) Plant Physiol. 64 930 935
Harris, R.W., Clark, J.R. & Matheny, N.P. 1999 Arboriculture: Integrated management of landscape trees, shrubs, and vines Prentice-Hall Upper Saddle River, NJ
Landhäusser, S.M. & Lieffers, V.J. 2001 Photosynthesis and carbon allocation of six boreal tree species grown in understory and open conditions Tree Physiol. 21 243 250
Lonsdale, W.M. & Smith, C.S. 2001 Evaluating pest-screening systems: Insights from epidemiology and ecology 52 60 Groves R.H., Panetta F.D. & Virtue J.G. Weed risk assessment CSIRO Collingwood, Australia
McCarron, J.K. & Knapp, A.K. 2001 C3 woody plant expansion in a C4 grassland: Are grasses and shrubs functionally distinct? Amer. J. Bot. 88 1818 1823
Nash, L.J. & Graves, W.R. 1993 Drought and flood stress effects on plant development and leaf water relations of 5 taxa of trees native to bottomland habitats J. Amer. Soc. Hort. Sci. 118 845 850
Ojeda, M., Schaffer, B. & Davies, F.S. 2004 Flooding, root temperature, physiology and growth of two Annona species Tree Physiol. 24 1019 1025
Schaffer, B., Andersen, P.C. & Ploetz, R.C. 1992 Responses of fruit crops to flooding 257 313 Janick J. Horticultural reviews Vol. 13 Wiley New York
Schrader, J.A., Gardner, S.J. & Graves, W.R. 2005 Resistance to water stress of Alnus maritima: Intraspecific variation and comparisons to other alders Environ. Exp. Bot. 53 281 298
Schrader, J.A. & Graves, W.R. 2003 Phenology and depth of cold acclimation in the three subspecies of Alnus maritima J. Amer. Soc. Hort. Sci. 128 330 336
Shevock, J.R., Ertter, B. & Taylor, D.W. 1992 Neviusia cliftonii (Rosaceae: Kerrieae), an intriguing new relict species from California Novon 2 285 289
Stewart, J.R. & Graves, W.R. 2004 Photosynthesis and growth of Rhamnus caroliniana during drought and flooding: Comparison to the invasive Rhamnus cathartica HortScience 39 1278 1282
Stewart, J.R. & Graves, W.R. 2006 Photosynthesis, growth, carbon allocation, and fruit load of Frangula caroliniana and Rhamnus cathartica Int. J. Plant Sci. 167 1161 1168
Westfall, P.H., Tobias, R.D., Rom, D., Wolfinger, R.D. & Hochberg, Y. 1999 Multiple comparisons and multiple tests using the SAS system SAS Inst Cary, NC