Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2011
Publication Date: 10/15/2011
Citation: Freeman, J.L., Banuelos, G.S. 2011. Selection of superior salt/boron tolerant Stanleya pinnata genotypes and quantification of their selenium phytoremediation abilities in drainage sediment.. Environmental Science and Technology. 45:9703-9710. Interpretive Summary: Excessive selenium (Se) in agricultural soils and in water sources is an important environmental issue in arid/semi-arid regions of the western U.S. Selenium is not considered an essential micronutrient for higher plants. Most plant species accumulate only low levels of Se and are generally termed non-accumulators of Se. There are, however, plants that can take up higher amounts of Se. These plants fall into a class termed hyperaccumulator plants, which hyperaccumulate Se to concentrations ranging from 2000 to 15000 ppm. Traditionally non-Se accumulator plants have been used as the "plant tool" in phytoremediation strategies for Se-tainted soils and waters in the westside of the San Joaquin Valley in central California (WSJV). In this study, we first tested four different ecotypes of Prince Plum, known as a hyperaccumulator, for their abilities to accumulate and volatilize se (transform Se into a gas) Se under typical soil conditions (high in salinity, boron, and Se) present in the WSJV. Our results clearly show that there are differences among the hyperaccumulator ecotypes for tolerating the adverse soil conditions and for accumulating and volaitilizing Se. They significantly accumulated and voalitilized more Se than non Se-accumulator plants like canola or mustard. The best performing hyper-accumulator ecotypes produced the greatest biomass and exhibited less toxicity symptoms (e.g., burnt leaves) than the susceptible ecotypes. We feel that the Prince Plum has great potential for use in phytoremediation strategies for managing excessive Se in saline soils of the Western U.S.
Technical Abstract: The semi-metallic mineral Se, a naturally-occurring trace element, is primarily found as selenate originating from sedimentary and shale rock formations, e.g., in the western side of the San Joaquin Valley of central California (WSJV). Because selenate-Se is water soluble, bioavailable and biomagnified by aquatic wildlife, selenate toxicity is a significant concern in drainage-impacted agricultural regions, e.g., WSJV. Phytomanagement of large agricultural fields with Brassica crops has been a practical tool to manage Se in central California. New plant species under consideration are selenium hyperaccumulator plants, e.g., Stanleya pinnata. They may be able to play a more effective role in the removal of Se because of their ability to tolerate, accumulate and volatilize significant amounts of Se. However, their salt and boron tolerance is unknown. Since Se is commonly present in conjunction with high salinity and B, plants used for the phytomanagement of Se must be highly saline and B tolerant. For this reason, we tested four unique ecotypes of S. pinnata for their abilities to accumulate and volatilize Se under high soil salinity, boron, and selenium conditions for two growing seasons. Soil quality was as follows; soil EC (electrical conductivity) ˜ 6 ds/m, and soluble B and Se concentrations of 6 and 1.3 mg/L, respectively. After two growing seasons, we observed a large amount of variability and growth inhibition, and necrotic leaves among the four ecotypes. Leaf Se concentrations ranged from 0.009 to a high of 1.62 mg Se/g DM, while average daily Se volatilization rates ranged from 55.3 to a high of 1055 µg Se/m2/d. Based upon plant Se concentrations, biomass yields, and volatilization rates, we estimated that we could remove from 10 to 20% of total Se present in the soil (0-30 cm) over a period of two years if no additional Se entered the soil profile. Clearly, genotypic variability existed within each ecotype tested in regards to salt/B tolerance, biomass production, Se hyperaccumulation and volatilization. Identifying and using the most salt and B ecotype of S. pinnata in Se-laden soils of the WSJV provides phytoremediation a more realistic opportunity to effectively manage saline/B soils high in Se.