Abstract: Cadmium (Cd) is a common abiotic stress factor in the environment. Screening germplasm resources for Cd tolerance is an effective way to develop plants for use in biofuel production on land contaminated by heavy metals. Switchgrass (Panicum virgatum) has been identified by the U.S. Department of Energy as having very high potential as a biofuel substrate. Hence, 14 switchgrass cultivars under hydroponic culture were treated with 0 (control) or 10 μmol·L^-1 Cd, and morphological and physiological traits were investigated. Root morphology data of switchgrass were obtained using an EPSON scanner and WinRHIZO software. Net photosynthetic rate was determined with the LiCor-6400 portable photosynthesis system and a spectrophotometer was used to determine root activity. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to examine Cd accumulation of switchgrass. Data for measured traits were transformed to units of statistical standard deviation by division by their standard error and aggregated with positive/negative sign reversal where relevant, so that Cd tolerance was additive across traits, and a composite index of Cd tolerance compiled. Lastly a cluster analysis was performed. It was found that Cd stress significantly reduced the root length, root surface area, number of root tips, total dry weight, net photosynthetic rate and root activity of different switchgrass cultivars to different degrees. Significant differences were found (P<0.01) among cultivars. According to composite index (D value), Kanlow was the most tolerant variety, while Foreburg was the least tolerant. On cluster analysis, the 14 switchgrass cultivars were classified into 3 Cd-tolerance types. One cultivar (Kanlow) had high Cd tolerance; 9 cultivars (Alamo, BoMaster, Carthage, Cave in Rock, Long Island, Newyork, Shawnee, Sunburst, Trailblazer) were medium-cadmium-tolerance types and 4 cultivars (Blackwell, Dacotah, Foresburg, Shelter) were Cd-sensitive types. It was also found that the cultivar Kanlow with high Cd tolerance had a strong ability to accumulate Cd. This study provides a theoretical basis for selecting suitable switchgrass cultivars for the cultivation of Cd-polluted land, and the results illustrate an operable method to evaluate the Cd tolerance of plant germplasm lines.

Key words: switchgrass, cadmium tolerance, subordination function, comprehensive evaluation