Tartaric acid soil-amendment increases phytoextraction potential through root to shoot transfer of lead in turnip

The phytoextraction potential of turnip and comparative effectiveness of three different organic ligands towards removal of lead (Pb) was investigated under field conditions. The 20 d old turnip seedlings were exposed to different Pb levels (0.0218, 2.42 and 4.83 mM Pb) spiked in the soil. After 10 d of Pb application, the soil was spiked with 2.4 mM concentration of different chelates viz. ethylenediaminetetraacetic acid (EDTA), citric acid (CA) and tartaric acid (TA). The 60 d old plants were harvested for growth analyses and determination of photosynthetic pigments, while Pb-concentration in different plant parts was determined from 60 and 90 d old plants. Yield attributes were recorded at the harvesting stage (HS, 90 d old plants). No suppression (rather a stimulation) in the root and shoot growth was evident upon Pb exposure whereas, a reduction in the chlorophyll content occurred at 4.83 mM Pb level. Soil amendment with TA improved chlorophyll contents irrespective of Pb levels while the effect of CA and EDTA was differential. A reduction in the root length while an increase in its diameter was recorded particularly at 4.83 mM Pb stress in 90 d old plants. The turnip retained maximum Pb-fraction in the roots at early growth stages, while EDTA application further increased its retention in root at 4.83 mM Pb regime. Nonetheless, only TA amendment promoted the transfer of Pb to shoot (∼30%) irrespective of Pb regimes. At the HS, application of both TA and EDTA caused substantial uptake of Pb in the root while the maximum shoot Pb-fraction was recorded again due to TA application, particularly at 4.83 mM Pb level. Above all, TA was identified as the most effective chelate that mobilized Pb from root to shoot leading to better growth possibly due to dilution effect, and thus enhanced phytoextraction efficiency in turnip.