https://aurora.auburn.edu/handle/11200/44136 2026-04-03T18:40:36Z https://aurora.auburn.edu/handle/11200/49946 Biology of Ultramafic Rocks and Soils: Research Goals for the Future https://aurora.auburn.edu/handle/11200/49945 Do Tropical Nickel Hyperaccumulators Mobilize Metals into Epiphytes? A Test Using Bryophytes from New Caledonia Hyperaccumulator plants mobilize large amounts of certain elements from the soil into their tissues. Those elements then may be transferred to other organisms in those communities. Using a humid tropical forest site in New Caledonia, we tested whether epiphytes (mosses and liverworts) growing on Ni hyperaccumulator hosts contained greater levels of Ni (and seven other metals) than those growing on non-hyperaccumulator hosts. We selected two Ni hyperaccumulator species, Psychotria douarrei and Hybanthus austrocaledonicus, pairing individuals of each species with similar-sized non-hyperaccumulators and collecting epiphytes from each for elemental analysis. Samples of epiphytes and host plant leaves were analyzed for concentrations of eight metals (Co, Cr, Fe, Mg, Mn, Ni, Pb, and Zn). Two-way ANOVA was used to assess the infl uence of host type (hyperaccumulator or non-hyperaccumulator), epiphyte group, and the interaction term. Leaves of both Ni hyperaccumulator species had greater Ni concentrations than the paired nonhyperaccumulator species, but leaf concentrations of other metals (Co, Cr, Fe, Pb, and Zn) were higher as well in one or both cases. The strongest infl uence on epiphyte elemental composition was found to be the host type factor for Ni. Epiphytes collected from hyperaccumulator hosts had signifi cantly greater Ni concentrations than those collected from non-hyperaccumulator hosts. Epiphyte Ni concentrations often exceeded the threshold used to defi ne Ni hyperaccumulation (1000 +g/g), showing that some epiphytes (in most cases those growing on Ni hyperaccumulators) also hyperaccumulate Ni. Six of the epiphytes we analyzed, four liverworts (Frullania ramuligera, Schistochila sp., Morphotype #1 and Morphotype #13) and two mosses (Calyptothecium sp. and Aerobryopsis wallichii), had at least one specimen containing more than 1000 +g Ni/g and hence qualify as Ni hyperaccumulators. We conclude that Ni could move from Ni hyperaccumulator hosts to their epiphytes, either from leachates/exudates from tissues or from accumulated external dust, thus potentially mobilizing Ni still further into the food webs of these humid tropical forests. https://aurora.auburn.edu/handle/11200/49944 Variation of Morphology and Elemental Concentrations in the California Nickel Hyperaccumulator Streptanthus polygaloides (Brassicaceae) The Ni hyperaccumulator Strepthanthus polygaloides (Brassicaceae) is one of a handful of Ni hyperaccumulators known from continental North America. Surveys have revealed four distinctive morphs of this species, relying primarily on floral traits (sepal color and shape): a purple sepal morph (P), a yellow sepal morph (Y), a morph in which sepals start yellow and mature to purple (Y/P), and a morph with light yellow undulate sepals (U). In this study, we raised plants from ten populations (five Y, three P, one Y/P, and one U) under uniform greenhouse conditions to determine if morphs varied in morphology and elemental concentrations when grown on Ni-amended potting soil in a common garden. Morphological data included measurements of leaf form (length, width, and degree of lobing) and plant size (height to first flower as they bolted in summer). Phenology was documented by noting flowering timing of plants. Elemental concentrations of plants were also determined for nine elements (Ca, Cu, Fe, K, Mg, Mn, Ni, P, and Zn). All morphological/phenological traits measured varied significantly between at least some morphs. The U and Y/P morphs were larger than Y and P morphs, with larger leaves as well. Leaves of U morph plants had wide sinuses and shallow lobes, whereas Y/P plants had narrow sinuses and long narrow lobes. P morph plants were shortest in stature, with the smallest leaves. Morphs also varied significantly in concentrations of all elements except Fe. All populations hyperaccumulated Ni, but the P morph contained significantly greater Ni levels than the other three morphs. The P morph also had more Mg, and less Mn and P, than the other morphs. The U morph had more K and Zn, but less Ca, than the other morphs. Principal components analysis revealed all four morphs to be distinctive from one another, and also suggested both morphological/phenological and elemental differences between Y morph populations along a north–south gradient. We conclude that there is considerable genetic divergence between morphs. If additional information shows that morphs are reproductively isolated, then these morphs may require taxonomic subdivision. https://aurora.auburn.edu/handle/11200/49943 Elemental Concentrations of Eleven New Caledonian Plant Species from Serpentine Soils: Elemental Correlations and Leaf-Age Effects - We investigated accumulation of elements (Ca, Co, Cr, Cu, Fe, K, Mg, Mn, P, Pb, and Zn) in leaves of different ages for 11 evergreen woody plant species from serpentine soils of New Caledonia. Species were classifi ed into four categories of Ni accumulation ability: one species was a non-accumulator (<100 mg Ni/ kg), three were accumulators (100–1000 mg Ni/kg), two were hyperaccumulators (1000–10,000 mg Ni/kg), and fi ve were hypernickelophores (>10,000 mg Ni/kg). We harvested leaves from each species, separating them into three (four in one case) relative age categories based upon their position along branches (younger toward the apex, older far from it). Leaf samples were dried, ground, and dry-ashed, and their elemental concentrations were determined by inductively coupled plasma spectrometry (all elements except Ni) or atomic absorption spectrophotometry (Ni). Great variation was found for most elements both within and among species, but Ni varied most (1050-fold between species for oldest leaves). Correlations between Ni and other transition metals showed no signifi cant relationships within samples of any species, but, we found signifi cant positive correlations between Ni and Pb (correlation coeffi cient = 0.97) and Ni and Fe (correlation coeffi cient = 0.87) among species. Leaf Ni concentrations varied signifi cantly with leaf age for two species, the hypernickelophores Geissois pruinosa and Homalium kanaliense. We conclude that Ni concentration varies markedly between species, but generally does not vary with leaf age within species. We also suggest that four Ni accumulation category terms— non-accumulator, hemi-accumulator, hyperaccumulator, and hypernickelophore—be used to subdivide the wide variation found in Ni concentrations in plant leaves.