Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2016
Publication Date: 8/23/2016
Citation: Banuelos, G.S., Arroyo, I.S., Dangi, S.R., Zambrano, C. 2016. Continued selenium biofortification of carrots and broccoli grown in soils once amended with Se-enriched S. pinnata. Frontiers in Plant Science. 7:1251. doi: 10.3389/fpls.2016.01251.
Interpretive Summary: Selenium biofortification of food crops has been practiced in selenium-deficient regions of different countries by adding inorganic-selenium containing fertilizers to soils, i.e., Finland, United Kingdom, New Zealand, and China. Applying inorganic selenium (Se) accurately at low rates on an annual basis can be especially difficult for untrained growers under variable field soil conditions or in countries with less developed farming methods and with a diverse set of cropping systems. Moreover, losses of Se can occur through leaching of soluble inorganic-Se by excessive precipitation/irrigation or by the volatilization of Se induced by microbial activities. Earlier studies were conducted by adding Se enriched plant material to soils as an organic source of Se. In all these studies, Se applied via organic matter was absorbed by the respective plant species. The question remained, however, must Se-enriched organic material be added on a regular basis to the soil prior to the planting of each subsequent crop at a given growing site? In this two-year biofortification field study, we evaluated the uptake of Se by carrots and broccoli grown in soils previously amended (3-4 years ago) with organic Se from a Se-hyperaccumulator plant (Prince’s Plum). In addition, we determined the forms of Se in broccoli and carrots in two growing seasons and identified the microbiological community in soils amended earlier with Se-enriched plant material. Results showed that both broccoli and carrots accumulated Se (primarily as selenomethionine) three and four years later after initial application of organic Se to the soil. In the soil, there was no difference in the microbiological community between Se-treated soils or control soils. Adding Se-enriched organic matter to the soil may be another strategy to effectively biofortify carrots and broccoli with selenium on a long-term basis.
Technical Abstract: Selenium (Se) biofortification has been practiced in Se-deficient regions throughout the world primarily by adding inorganic sources of Se to the soil. Adding organic sources of Se could be useful as an alternative Se amendment for the production of Se-biofortified food crops needed in Se-deficient countries. In this multi-year micro-plot study, we investigated the accumulation of Se in carrots and broccoli grown in soils that had been previously amended with Se-enriched Stanleya pinnata (Prince’s Plum) three and four years prior to planting one and two, respectively. Results showed that total and extractable Se concentrations (1:1 soil:water) in soils (0-30 cm) were 1.65 mg kg-1 and 88 µg L-1, and 0.92 mg kg-1 and 48.6 µg L-1 at the beginning of the growing season for planting one and two, respectively. After each respective growing season, total Se concentrations in the broccoli florets and carrots ranged from 6.99 to 7.83 mg kg-1 and 3.15 to 6.25 mg kg-1 in planting one and two, respectively. In broccoli and carrot plant tissues, selenomethionine was the predominant selenoamino acid identified in Se aqueous extracts. In postharvest soils from planting one, phospholipid analyses (PLFA) showed that amending the soil with S. pinnata exerted no effect on the microbial biomass, arbuscular mycorrhizal fungi, actinomycetes and Gram-positive and bacterial PLFA at both 0-5 and 0-30 cm, respectively. Successfully producing Se-enriched broccoli and carrots three and four years later after amending soil with Se-enriched S. pinnata clearly demonstrates its potential long-term source as an organic Se enriched fertilizer for Se-deficient regions.