NICKEL HYPERACCUMULATION BY THLASPI-MONTANUM VAR. MONTANUM (BRASSICACEAE) - A CONSTITUTIVE TRAIT

Adaptations to particular stresses may occur only in populations exper iencing those stresses or may be widespread within a species. Nickel h yperaccumulation is viewed as an adaptation to high-Ni (serpentine) so ils, but few studies have determined if hyperaccumulation ability is r estricted to populations from high-Ni soils or if it is a constitutive trait found in populations on both high-and low-Ni soils. We compared mineral element concentrations of Thlaspi montanum var. montanum plan ts grown on normal and high-Ni greenhouse soils to address this questi on. Seed sources were from four populations (two serpentine, two non-s erpentine) in Oregon and northern California, USA. Plants from all pop ulations were able to hyperaccumulate Ni, showing Ni hyperaccumulation to be a constitutive trait in this species. Populations differed in t heir ability to extract some elements (e.g., Ca, Mg, P) from greenhous e soils. We noted a negative correlation between tissue concentrations of Ni and Zn. We suggest that the ability to hyperaccumulate Ni has a daptive value to populations growing on non-serpentine soil. This adap tive value may be a consequence of metal-based plant defense against h erbivores/pathogens, metal-based interference against neighboring plan t species, or an efficient nutrient scavenging system. We suggest that the Ni hyperaccumulation ability of T. montanum var. montanum may be an inadvertent consequence of an efficient nutrient (possibly Zn or Ca ) uptake system.