Cytotypes of Centaurea stoebe found to differ in root growth using growth pouches

Centaurea stoebe is native to Europe and Western Asia and was introduced into North America in the late 19th century, where it has become highly invasive. In its native range, C.stoebe occurs in two cytotypes, namely diploids (2n=18) and tetraploids (2n=36), but only the tetraploid form has been identified in the invaded range. We used special growth pouches to determine whether diploid and tetraploid cytotypes from the native range differed in root growth and architecture. We grew seeds from five populations of each cytotype in growth pouches during a period of sixteen days and measured root growth traits both by hand and using a root-scanning software package (WinRHIZO). Tetraploid cytotypes had significantly larger total root length, taproot length, surface area, root volume, above- and below-ground biomass and root to shoot ratios than diploid cytotypes. We suggest that increased early root growth of tetraploid cytotypes as compared with diploids may be one factor that pre-adapted them towards the colonisation of warmer and drier climates in Europe and North America, where tetraploids are currently expanding and invasive respectively.