Continued Selenium Biofortification of Carrots and Broccoli Grown in Soils Once Amended with Se-enriched S. pinnata

Abstract

Selenium (Se) biofortification has been practiced in Se-deficient regions throughout the world primarily by adding inorganic sources of Se to the soil. Considering the use of adding organic sources of Se could be useful as an alternative Se amendment for the production of Se-biofortified food crops. In this multi-year micro-plot study, we investigate growing carrots and broccoli in soils that had been previously amended with Se-enriched Stanleya pinnata Pursh (Britton) three and 4 years prior to planting one and two, respectively. Results showed that total and extractable Se concentrations 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, SeMet (selenomethionine) was the predominant selenoamino acid identified in Se aqueous extracts. In postharvest soils from planting one, phospholipid fatty acid (PLFA) analyses showed that amending the soil with S. pinnata exerted no effect on the microbial biomass, AMF (arbuscular mycorrhizal fungi), actinomycetes and Gram-positive and bacterial PLFA at both 0-5 and 0-30 cm, respectively, 3 years later. Successfully producing Se-enriched broccoli and carrots 3 and 4 years later after amending soil with Se-enriched S. pinnata clearly demonstrates its potential source as an organic Se enriched fertilizer for Se-deficient regions.

Keywords: Stanleya pinnata; biofortification; broccoli; carrots; selenium.

FIGURE 1

Total Se concentrations in broccoli florets grown in soil amended with Se at different rates of S. pinnata for planting one and two. Each value represents the mean of six replicates with standard deviation bars for both soil (x-axis) and plants (y-axis). Different letters within each column represent a significant difference at the *P < 0.05, **P < 0.001 level. Treatments correspond to amounts of Se added via S. pinnata (mg Se m^-2): T0(0), T1(105.4), T2(210.7), T3(421.4), and T4(842.9).

FIGURE 2

Total Se concentrations in carrots grown in soil amended with Se at different rates of S. pinnata for planting one and two. Each value represents the mean of six replicates with standard deviation bars for both soil (x-axis) and plants (y-axis). Different letters within each column represent a significant difference at the *P < 0.05, **P < 0.001 level. Treatments correspond to amounts of Se applied via S. pinnata added (mg Se m^-2): T0(0), T1(105.4), T2(210.7), T3(421.4), and T4(842.9).

FIGURE 3

Total phospholipid fatty acids (PLFAs) in Se amended soils grown with (carrot T4 and broccoli T4) and without (carrot T0 and broccoli T0) at 0–15 and 5–30 cm depths. Different letters represent a significant difference at the P < 0.05 level for each respective depth. Values represent the mean (n = 6) and standard deviation bar.

FIGURE 4

Gram+, Gram-, Fungal, AMF, Actinomycetes, and Eukaryotic PLFAs in Se amended soil grown with (carrot T4 and broccoli T4) and without (carrot T0 and broccoli T0) at 0–5 and 5–30 cm depths. Different letters represented a significant difference at the p < 0.05 level for each respective depth. Values represent the mean (n = 6) and standard deviation bar.