Difference of selenium uptake and transport of three vegetables in natural selenium-enriched soils

Objectives The absorption and transformation of Se-sensitive vegetables in natural Se-rich soils were studied, in order to provide theoretical and technical guidance for the production of Se-enriched vegetables.

Methods A pot experiment was conducted using garlic, mustard and spinach as tested vegetables. The treatments were four soils containing different total Se contents, which were used as the treatments marked as S_0.29, S_0.58, S_0.98 and S_2.07 in turn. Mustard and spinach samples were collected at the 40th, 53th, 68th and 82th day after transplanting, and harvested at the 97th day; garlic samples were collected at the 42th, 68th, 82th and 120th day, and harvested at the 165th day since transplanting. The plant samples were weighed, and the total and organic Se contents were analyzed as required. The uptake and translocation rate of Se in the vegetables were calculated. The contents of different Se fractions in the four soils were measured.

Results Mustard was the most sensitive to soil Se among the three vegetables. The fresh biomass of edible parts of mustard was the highest in Se_0.29, and those of spinach and garlic were the highest in Se_0.58 treatment, which was significantly different from that of Se_2.07 treatment. Se content in shoots of three vegetables showed an increasing trend in the whole growth period, and all followed by the order of garlic > mustard > spinach in different growth periods. The Se contents in all parts of vegetables were increased with the increase of soil Se contents, from 0.29 mg/kg to 2.07 mg/kg. The Se contents in shoot and root treated with Se_2.07 were 8.63 and 7.10 times of those treated with Se_0.29 in spinach, 12.25 and 23.29 times in mustard, while 39.92 and 4.90 times in garlic bulb and leaf. The Se contents in vegetable edible parts were in order of garlic (7.25–289.42 μg/kg) > mustard (1.22–14.94 μg/kg) > spinach (0.73–6.3 μg/kg). The Se contents in underground parts were all higher than those in aboveground parts. The Se content in root was 4.8, 12.6 and 8.22 times higher than that in stem and leaf in Se_2.07 treatment in the growth of spinach, mustard and garlic, respectively. The garlic and mustard could enrich Se from Se rich soils, and the absorption coefficients were 3.06–8.47 times and 1.58–5.8 times of that in spinach, respectively. Garlic and mustard grown in Se_0.98 and Se_2.07 soils reached the Se-rich standard for vegetable except for spinach in this study. The proportion of organic Se content in edible parts of these vegetables accounted for 73.5%–84.7%, which was increased with the increased Se content in soils. The organic Se proportion in Se_2.07 treatment was significantly higher than that in Se_0.29 treatment. Thus, the vegetable Se contents were not only related to the total soil Se contents, but also positively linked with the available Se contents in soils.

Conclusions Vegetable type and soil selenium content all affect the absorption, transformation and enrichment of selenium in vegetables. Three kinds of vegetables are sensitive to selenium content in soil, and mustard is the most sensitive. The selenium content and the conversion rate of organic selenium in edible parts increase with the increase of soil selenium content and show a significant positive correlation with the total selenium content and available selenium content in soil. The selenium enriching ability is garlic > mustard > spinach, the selenium content in garlic and mustard grow on the naturally selenium rich soil easily reachs the selenium rich vegetable standard, but spinach does not show the selenium rich ability. Therefore, although high soil selenium content affects the growth of garlic and mustard, garlic and mustard have a strong ability to transfer selenium to edible parts and can be used as selenium-rich vegetables.