Mechanism of nitrogen, phosphrous and potassium combined application promote absorption, transportation and accumulation of Pb in sunflower (Helianthns annuus L.)

Objectives Sunflower (Helianthns annuus L.) has an huge potential for phytoremediation of lead (Pb) contaminated soils. This study investigated the effect of fertilizers on the Pb absorption and transportation mechanisms in different sunflower species, which helped to improve the Pb phytoextraction efficiency with rational fertilizations. The results will provide theoretical and technological support for reasonable phytoremediation of a large area of mild and moderate Pb contaminated soils in China using sunflower.

Methods A pot experiment was conducted using a Pb-contaminated soil (total Pb 174 mg/kg) in northern China. Three sunflower cultivars, namely LD5009 (edible sunflower), T562 (oil sunflower) and Huanlehuopaozhu (Hhz, ornamental sunflower), were used as tested materials, and fertilizer treatments of CK, N, NP, NPK were setup for each cultivar. At the 40th day after transplanting, the sunflower plants were harvested, and the biomass, Pb concentration, subcellular compartmentalization were determined, at the same time the pH value and the contents of different Pb forms in rhizosphere soil of three sunflower species were measured.

Results There were significant differences in Pb accumulation capacity among three sunflower species, and the highest shoot Pb content was in LD5009, which was 1.6 and 1.7 times as high as that in Hhz and T562. Application of fertilizers significantly promoted the growth of the three cultivars and the absorption and transportation of Pb in them. The Pb contents in shoots of LD5009, Hhz and T562 under NPK treatments were 184, 112 and 108 μg/plant, respectively, which were significantly higher than those under other treatments (P < 0.05). The results of Pb subcellular distribution in leaf of sunflower showed that Pb was mainly compartmented in metal-rich granule fraction (56.1%–86.4%) and cellular debris fraction (8.1%–38.3%). Application of fertilizers significantly increased the Pb concentration in cellular debris and metal-rich granule fraction (P < 0.05). The study on the Pb forms in rhizosphere soil of sunflower showed that although the NP and NPK fertilizers treatments lead to reduction of acid soluble Pb, the promotion effect of fertilizers application on root and shoot growth of sunflower was far greater than that on the reduction of soil Pb availability, which consequently promoted Pb absorption and transportation of sunflower.

Conclusions LD5009 is a good candidate for phytoremediation of mild and moderate Pb contaminated soil. N, P, K combined application effectively promotes the growth of sunflower, as well as increases the Pb absorption and transportation in sunflower, therefore effectively improves the Pb phytoextraction efficiency in sunflower.