Some Effects of Vanadium on the Growth and Development of the Gemmalings of Two Species of Thallose Liverworts

Abstract

Gemmalings of the thallose liverworts Marchantia polymorpha L. and Lunularia cruciata L. were treated with differing concentrations and chemical forms of vanadium. For both species, vanadium applied as the metavanadate ion (VO,-) was less toxic than when applied as the vanadyl cation (V02+), although Lunularia showed a more sensitive response. Urban and rural populations ofM. polymorpha showed differential responses to VO,- and V02+; urban gemmalings showing tolerance to VO2+ and rural populations to VO,-. Excessive vanadium levels, irrespective of chemical form, produced the following toxicity symptoms in M. polymorpha: reduced growth, necrosis, chlorosis and reduction/inhibition of rhizoid development. In L. cruciata, conspicuous oil bodies changed colour from light brown to black at elevated vanadium levels. The results are discussed in terms of vanadium occurrence in the biosphere, the chemistry of vanadium, the role of this element in plant nutrition, and in terms of the toxicity of other trace metals in the same biological system. Vanadium is a widely distributed and relatively abundant element. In the earth's crust, vanadium occurs at a mean concentration of 100 ppm, and can be found in at least 50 different minerals (car- notite, roscoelite, vanadinite and petronite are most abundant). Substantial amounts of this element are also found in certain crude oils and petroleum ashes. It can also be associated with phosphate rocks, iron ores and oil shales. Crude oil may contain up to 1400 ppm vanadium, and residuals from Venezue- lan oil can contain 200-1000 ppm (Bengtsson & Tyler 1976). The chemistry of this element is complex. It can be found in four oxidation states (2, 3, 4 and 5), and readily forms complexes with oxygen. In nature it is thought to occur as vanadate or in organo- vanadium complexes. Thus, its stability and hence availability to plants depends on the geochemical and physical environment; in reducing or alkaline conditions in the presence of carbonate, it is soluble, but when oxidizing in the presence of potassium or calcium or in reducing conditions in the presence of organic matter, it is precipitated. Vanadium in the atmosphere can arise from nat- ural sources (weathering of rocks, marine aerosols) or from man-made sources. The largest man-made vanadium emissions result from combustion of re-