Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 15, 2002
Publication Date: N/A
Interpretive Summary: Our earlier work indicated that a commercial technology could be developed to produce Ni hyperaccumulator plants to phytoextraction Ni from contaminated or mineralized soils at lower cost that traditional mining technology. This phytomining technology obtained support through a Cooperative Research and Development Agreement. The project was the domestication of a new farm crop and all that implies. Germplasm was collected in Europe, evaluated under uniform soil conditions, and plant breeding used to produce improved cultivars. Fertilizer requirements were measured by pot and field experiments. Other soil management practices were evaluated and optimized. Herbicides were identified which controlled common weeds in Ni rich soils. Wide genetic variation in Ni hyperaccumulation ability, and in harvestable yield/plant habit were observed. Alyssum murale grown on several Oregon, USA, serpentine soils, and on Ontario, Canada, smelter contaminated soils, accumulated up to 2.0% Ni in whole shoots; leaves contained about double the Ni of stems and petioles. Harvest should be scheduled before leaves are dropped during seed filling in June. Perennial culture can reduce production costs, and normal hay making farm equipment was effective in growing and harvesting Alyssum biomass for sale. One very unexpected finding was that increasing soil pH promoted higher Ni phytoextraction, which is opposite the effect of increasing soil pH on the solubility of soil Ni. But other elements whose uptake is normally reduced at higher pH (Zn, Co, Mn) had reduced uptake by Alyssum at higher soil pH. The overall project provides a new commercial farm crop for growers who farm serpentine soils or Ni contaminated soils.
We have made important progress in developing a commercial technology using hyperaccumulator plant species to phytoextract nickel (Ni) from contaminated and/or Ni-rich soils. Development of such a technology required identifying or creating an ideal phytoextraction plant, optimizing soil and crop management practices for biomass production, and development of methods for biomass processing and Ni extraction. An on-going program is being carried out to develop a genetically improved phytoextraction plant that combines favorable agronomic and Ni accumulation characteristics. We collected genetically diversified Ni hyperaccumulator species and ecotypes of Alyssum. Greenhouse pot tests and field evaluation were conducted using serpentine and Ni-refinery contaminated soils. Large genetic variation was found; mean shoot Ni concentrations in field grown plants ranged from 4200 to 20400 mg kg-1. We have been studying several soil management practices that may affect the efficiency of Ni phytoextraction. Soil pH is an important factor affecting absorption of metals by plants. An unexpected result of both greenhouse and field experiments was that Ni uptake by two Alyssum species was reduced at lower soil pH and increased at higher soil pH. At higher pH, plant yield was improved also. In soil fertility management studies, we found that N application significantly increased plant biomass, but did not affect plant shoot Ni concentration. Planting methods, population density, weed control practices, harvest schedule and methods, pollination control, and seed processing needs for commercial phytomining were established. The progress made in our recent studies will enable us to apply this technology commercially in the near future.