| Cadmium (Cd) pollution in farmland soils has become a significant environmental problem of great concern. In most instances, the toxic Cd in soil can be easily uptake by plant and thereby a reduction in crop yield and qualities are usually observed. Additionally, it may pose serious threat to human health through the food chain. Previous studies have reported that in Cd-contaminated soil, different nitrogen (N) forms fertilizers application could cause significant differences in the growth and Cd accumulation in crop plants. However, the effect of slow release N fertilizer, a commonly used chemical fertilizer, on the growth and Cd accumulation of the crops grown in Cd-contaminated soil is still unclear. Therefore, instant soluble N fertilizer types (ammonium, nitrate and amide) and slow released fertilizers were simultaneously employed in present research to study their effects on the growth and Cd concentration in the Cd-contaminated Chinese cabbage pakchoi, the widely cultivated vegetable species in China. In addition, the possibility of alleviates Cd-induced oxidative stress by combinations of dicyandiamide (DCD) with ammonium-N and urea fertilizers were also studied. The major results and conclusions were summarized as follows:(1) In ammonium, nitrate and urea fertilizers application treatments,5mg kg-1Cd-contaminated soil decreased the fresh weights of the edible parts of pakchoi by83.5%,37.6%and68.4%, respectively. The Cd tolerance index (TICd) of pakchoi with nitrate fertilizer treatment was77.1, which was2.5times for ammonium and2.7times for urea application groups. Investigations on photosynthesis, oxidative stress (superoxide anion radical [O2-] producing rate, hydrogen peroxide [H2O2] and malonaldehyde [MDA] concentration) and Cd concentrations of pakchoi all showed that5mg kg-1Cd would induce significant growth stress and higher Cd concentrations in all above three fertilizers treatments. Notably, the Cd-induced stress was more serious in ammonium-N and urea fertilizers treatments.(2) Under5mg kg-1Cd stress, the fresh weight of the edible parts of pakchoi in slow release fertilizer treatment increased by132%as compared with the control (ammonium:nitrate [1:1] instant soluble fertilizer). Application of slow release fertilizer to Cd-stressed plants further alleviated the oxidative stress by decrease the O2-producing rate, H2O2and MDA concentrations in their leaves by16%,19%and25%, respectively, as compared with the levels in the control treatment. In addition, slow release N fertilizer treatment also lowered the Cd concentrations in leaves and stems of pakchoi by45%and49%, respectively. More interestingly, the fresh weight of edible parts, the photosynthesis parameters and oxidative stress indexes of pakchoi with the slow release N fertilizer application showed no statistically significant differences between the treatment and the control (0mg kg-1Cd-contaminated soil). In conclusion, the study presents the comparative potential of applied slow release N fertilizer in Cd-contaminated soil, which not only increases vegetable productivity, but also decreases Cd concentration in plants, compared with the instant soluble N fertilizer treatment.(3) In5mg kg-1Cd-contaminated soil, combination of60mg kg-1DCD with ammonium and urea fertilizer significantly enhanced the fresh weight of pakchoi shoots by583%and207%, respectively. However, combined application of DCD hadn’t significantly improved pakchoi growth in nitrate fertilizer treatment. The changes in parameters which reflect the photosynthesis and oxidative stress also showed that DCD combined application in ammonium and urea fertilizers treatments could alleviate Cd stress in pakchoi. Besides, DCD combined application in Cd-contaminated soil resulted in a much lower level of Cd concentration in edible parts of pakchoi in both ammonium and urea fertilizer treatments. Compared with the control (0mg kg-1DCD), Cd concentrations in the leaves and stems had58%and62%more decreases, respectively in ammonium fertilizer treatment and45%and56%more decreases, respectively in urea N fertilizer treatment. However, no significant changes observed in nitrate fertilizers treatment. Keeping in mind all of the above, we concluded that combined application of DCD with ammonium and urea fertilizers in Cd-contaminated soil can effectively alleviate Cd-induced growth inhibition and Cd concentrations in plants. |
PDF Full Text Request