Enhanced Rhizosphere Bacterial Population in an Abandoned Copper Mined-out Area Planted with Jatropha Interspersed with Selected Indigenous Tree Species
Rehabilitation was conducted in an abandoned copper mined-out area in Mogpog, Marinduque by interplanting Jatropha curcas, a biodiesel source and potential phytoremediator, with different reforestation tree species, Pterocarpus indicus, Cassia spectabilis, Lagerstroemia speciosa and Bauhinia purpurea. The effect of the diversification treatment on the rhizosphere bacterial population, known to promote growth of host plant, was analyzed within a fifteen-month period (August 2007 to November 2008). The number of cultivable soil bacteria on-site prior to planting was very low (<0.01 to 2 x 103 CFU per g) owing to soil’s acidity (pH 5) and poorly nourished condition. Higher bacterial population was observed from Jatropha rhizosphere than soil without vegetation. Bacterial population also varied with diversification treatments. Highest populations (7.3 x 104 to 1.3 x 105 CFU per g) of Cu-, Pb- and Zn resistant bacteria were observed where in Jatropha was interplanted with Pterocarpus, Cassia, and Lagerstroemia. It appears that such treatment enhanced the population of heavy metal-resistant rhizosphere bacteria in Jatropha indicative of its potential in bioremediation. Randomly selected isolates were identified as Arthrobacter oxydans, Klebsiella variicola and Bacillus spp, which are all common soil bacteria. Rehabilitation of abandoned, mined-out areas can thus be naturally promoted by diversifying plants being introduced in such sites as this would enhance rhizosphere bacterial population.