Uptake and translocation of metals in fenugreek grown on soil amended with tannery sludge: involvement of antioxidants

Agricultural and industrial activities cause heavy metal pollution in the soil, which adversely affect the plant growing therein. The plants of fenugreek (Trigonella foenum-graecum L.) were grown in soil amended with different percent of tannery sludge (TS) (10%, 25%, 35%, 50%, and 100% TS) in order to study the effect on antioxidant levels due to translocation of metals (Fe, Zn, Mn, Cu, Cr, Pb). The accumulation of the metals was found more in shoots than roots, except Fe and Cr. The level of metals in seeds of the plant increased with increase in sludge amendments ratio except Mn, which decreased in roots, shoots, and seeds of the plant. Chromium was found below detection limits in the seeds at 10% and 25% TS. Correlation coefficient (r) between total metal accumulation and extractable metals showed that Zn (P<0.01), Cr (P<0.01), and Cu (P<0.05) are significantly correlated, whereas, correlation with pH showed significant positive relation with all the studied metals except Mn. Significant positive correlation was recorded between metal accumulation (Fe, Zn, Cu) and electrical conductivity, cation exchange capacity, and organic matter, however, Zn, Cr, and Cu showed significant positive correlation with bulk density, nitrate, ammonia, and available phosphorus. The analysis of the results showed that total chlorophyll content showed significant (P< 0.5) increase in lower amendment of sludge (up to 35% TS at 30 d and 25% TS at 60 d) as over their controls. In roots, malondialdehyde, cysteine, non-protein thiol, proline, protein, ascorbic acid contents increased up to 35% TS at 30 d. Principal component analysis also showed that strong association exists among malondialdehyde, nonprotein thiol, protein, and cysteine contents in the plants grown on different amendments of TS. The level of antioxidants increased which enabled the plant to cope up the stress induced in the plants grown on lower amendments of TS, however, toxicity was observed at higher amendments.