Contribution of mycorrhizal inoculation on heavy metal accumulation by Jatropha curcas L. in marginal and mine soils for better plant health

The establishment of the Jathropha curcas L. plantations aims to restore the productivity of the heavy metal (HM) contaminated areas such as marginal grasslands and mine sites in the country. J. curcas has been recently tapped as alternate source of oil for biodiesel. This study aimed to determine the survival, growth and HM such as copper (Cu), zinc (Zn), Iron (Fe) and manganese (Mn) accumulation by J.curcas seedlings and cuttings in mine soil collected from abandoned mines in Mogpog, Marinduque and Paracale, Camarines Norte and in grassland soil from Caliraya, Laguna. Plants were either uninoculated or inoculated with a commercial (MYKOVAM) or indigenous (MineVAM) mycorrhizal inoculant. Results showed that J.curcas isa capable of growing and surviving in HM- contaminated soils. Among the three soils, survival and growth was lowest in Mogpog soil and highest in Paracale soil. Mycorrhizal inoculation generally enchanced the survival and growth of J. curcas seedlings. However, growth of the cuttings was not significantly affected by inoculation which may be due to their lower percentage mycorrhizal infection (0-10%) as compared to the seedlings (2-66%). MYKOVAM promoted higher survival of J. curcas than Mine VAM because of its higher infection in the roots of the plants. In terms of growth, MYKOVAM enhanced root growth while MineVAM enhanced shoot growth. Cu accumulation was observed to be higher in cuttings whereas, Zn, Fe and Mn accumulation were higher in seedlings. In Paracale soil, MYKOVAM-inoculated plants had the highest Cu concentration while the highest Zn, Fe and Mn were observed in Mine VAM-inoculated ones. In Caliraya soil, Cu, Zn and Fe were highest in MYKOVAM-inoculated plants while the highest Mn was observed in Mine VAM-inoculated plants. In both soils, roots accumulated the most HMs while the stem had the lowest. These observations confirm that mycorrhiza alleviate metal toxicity in plants by accumulating and retaining HMs in the roots there by reducing metal accumulation to the aerial parts. This implies that mycorrhizal inoculation of this plant is important to ensure that only trace amounts of HMs may accumulate up to the seeds where oil is extracted for biodiesel. Thus, J. curcas can be used to rehabilitate abandoned mine sites and marginal grasslands and that mycorrhizal inoculation plays a significant role in promoting better plant health in stressed environment as well as facilitating HM clean up of unproductive soils.