Abstracts Biological Sciences

Trace elements in New Zealand plants

by Graeme Lester Lyon

In biogeochemical studies initiated for the first time in New Zealand, some trace elements in indigenous plants and in the soils supporting these plants, were determined by emission spectrography and atomic absorption spectrophotometry. A test of the biogeochemical method of prospecting was made by studying elemental concentrations in leaves of three tree species and in the corresponding soils from mineralised and non-mineralised ground at Copper-stain Creek, North-West Nelson. All samples were analysed for copper and molybdenum. Olearia rani was also analysed for zinc. Elemental contents in plants and soils were compared by correlation calculations on a computer. The molybdenum content of the ash of O. rani leaves showed a highly-significant correlation with the content of the same element in corresponding soil samples. This indicated that O. rani could be used as a biogeochemical indicator for molybdenum mineralisation. No other significant plant-soil correlations were found for molybdenum., copper or zinc. For a further set of O. rani samples, leaves, twigs, wood and flowers were all analysed for zinc, copper and molybdenum. This data showed that the leaves of O. rani were better than the other parts of the plant, and that analyses based on ash weight were better than dry weight values for indicating molybdenum mineralisation in the soil. Cumulative frequency diagrams gave values for threshhold concentrations used to delineate the anomalous areas at Copperstain Creek. Molybdenum contents in the ash of plants showed wide variations, ranging from one to 1600 parts per million. Copper and zinc contents showed less variation but there were significant differences in the mean values for each species. A New Zealand serpentine flora and the associated soils from near Dun Mountain on the Nelson Mineral Belt was studied. In an initial orientation survey, it was found that seventy-one samples of twenty-six species showed that wide variations existed in the concentrations of the elements chromium, nickel, cobalt and copper. Six of these species were sampled further and analysed for chromium, nickel, copper, cobalt, calcium and magnesium. The species Cassinia vauvilliersii, Hebe odora and Leptospermum scoparium were sampled both randomly and from a localised area of serpentine where soils were more uniform. Plant elemental contents were found to vary up to several orders of magnitude in both sets of samples. Specimens of the same species sampled from near the boundary of serpentine with sedimentary rocks and from an andesitic area at Mt. Egmont, contained much lower amounts of chromium, nickel, cobalt and magnesium and higher amounts of calcium than samples from serpentine. Correlation coefficients were calculated for the relationships between pairs of elements and showed that for C. vauvilliersii, there were highly-significant correlations between plant ash and soil contents for chromium, nickel and cobalt. H. odora and L. scoparium showed similar but less pronounced correlations for the same three elements. It was concluded…