Latitudinal variation in cold hardiness in introduced Tamarix and native Populus

Abstract

To investigate the evolution of clinal variation in an invasive plant, we compared cold hardiness in the introduced saltcedar (Tamarix ramosissima, Tamarix chinensis, and hybrids) and the native plains cottonwood (Populus deltoides subsp. monilifera). In a shadehouse in Colorado (41°N), we grew plants collected along a latitudinal gradient in the central United States (29–48°N). On 17 occasions between September 2005 and June 2006, we determined killing temperatures using freeze-induced electrolyte leakage and direct observation. In midwinter, cottonwood survived cooling to −70°C, while saltcedar was killed at −33 to −47°C. Frost sensitivity, therefore, may limit northward expansion of saltcedar in North America. Both species demonstrated inherited latitudinal variation in cold hardiness. For example, from September through January killing temperatures for saltcedar from 29.18°N were 5–21°C higher than those for saltcedar from 47.60°N, and on September 26 and October 11, killing temperatures for cottonwood from 33.06°N were >43°C higher than those for cottonwood from 47.60°N. Analysis of nine microsatellite loci showed that southern saltcedars are more closely related to T. chinensis while northern plants are more closely related to T. ramosissima. Hybridization may have introduced the genetic variability necessary for rapid evolution of the cline in saltcedar cold hardiness.

Assessment of Tannin Variation in Tamarisk Foliage Across a Latitudinal Gradient

“…Tamarisk foliage was collected from a common garden planted in a clay-loam field on 16 August 2005 in Fort Collins, Colorado from rooted cuttings [11]. Tamarisks in the garden were Tamarix ramosissima Ledeb., T. chinensis Lour., and hybrids of the two.…”

“…Microsatellite markers showed gradual latitudinal genetic variation. Collections from southern locations were more similar to T. chinensis while collections from northern locations were more similar to T. ramosissima [11]. Sample foliage (leaf and stem) was collected on 12 June 2007 from 161 genetically distinct individuals.…”

“…Other traits, such as cold hardiness, have been found to vary with latitude of origin [11]. Thus, we evaluated tannin concentrations across this same gradient.…”

Stress-Tolerant Feedstocks for Sustainable Bioenergy Production on Marginal Land

“…Populus deltoides ssp. monilifera survived cooling to −70°C [227]. Robinia pseudoacacia C3 High Withstands cold and freezing temperatures by increasing fatty acid concentration [228] and protein synthesis in bark cells [229,230], and produces glycoproteins to prevent ice crystal formation in cells.…”

“…For example, the phenomenon of cellular "supercooling" is common among conifer species, and some Pinus species can survive temperatures as low as −196°C [202]! Other cold-hardy woody crops include Populus [75,227] and Salix spp. [86,234] (Table 4) (Table 4).…”