Survival, Growth and Copper Accumulation of Jatropha curcas L. (tubang-bakod) in Marginal Grassland and Mine Waste Soils as Affected by Mycorrhizal Inoculation

Abstract

Copper contamination of soils generated by anthropogenic activities result in unproductive mine waste areas and marginal grasslands. The establishment of Jatropha curcas plantations aims to restore the productivity of these areas. This study determined the survival, growth, and Cu accumulation of J. curcas seedlings and cuttings in abandoned mine soils collected from Mogpog, Marinduque and Paracale, Camarines Norte and marginal grassland soil from Caliraya, Laguna. The study also determined the effect of mycorrhizal inoculation of soil on J. curcas. Results showed that J. curcas is capable of growing and surviving in Cu-contaminated soils. Among the three soils, survival and growth was lowest in Mogpog soil which may be due to the highly toxic Cu level (1600 pg g’1) present in the soil. Survival and growth was highest in Paracale soil because of its relatively low Cu content (45 pg g'1). Cu accumulation was higher in plants grown in Caliraya soil than in Paracale soil due to its higher Cu content available for plant uptake. Mycorrhizal inoculation generally enhanced the survival and growth of J. curcas seedlings. Inoculated seedlings possibly absorbed more essential nutrients from the soil as a consequence of the increase in root absorptive area conferred by mycorrhizal fungi to the plants. However, the survival of J. curcas cuttings was not significantly affected by inoculation which may be due to their lower percentage mycorrhizal infection as compared to the seedlings. Cu accumulation was also higher in inoculated plants. This supports previous findings that mycorrhizal fungi generally adsorb heavy metals such as Cu in the mycelium for their growth, thereby enhancing heavy metal accumulation of the plants. Between the two inoculants, commercialized (MYKOVAM) fungi promoted higher survival of J. curcas than indigenous (Mine VAM) fungi because of its higher infection in the roots of the plants. In terms of growth, both inoculants exhibited comparable effectiveness on both seedlings and cuttings. Cu accumulation was observed to be highest in the roots of plants grown in MYKOVAM-inoculated soils. This suggests that MYKOVAM is the most effective inoculant in terms of removing more Cu from the soil as well as alleviating Cu toxicity in plants by accumulating and retaining the metals in the roots. This mechanism thereby reduces further metal accumulation in the aerial parts which are sources of important medicinal and industrial products such as biodiesel. Thus, the planting of Jatropha curcas in mycorrhizal-enriched soils offers great potential in rehabilitating abandoned mine and marginal grassland soil.