The Efficacy of compost, limestone and growth of Leucaena leucocephala (Lam.) de wit, Senna siamea (Lam.) and Eucalyptus grandis W. Hill ex Maid. for the restoration of bacterial functional diversity in the rhizosphere in copper tailings and pyrite soils

Abstract

The potential of compost, limestone and growth of Leucaena leucocephala (Lam.) de wit, Senna siamea (Lam.) H.S Irwin & Barneby, and Eucalyptus grandis W. Hill ex Maid for the restoration of rhizospheric bacterial functional diversity of pyrite soil and copper tailings was assessed in the field. Pyrite soil and copper tailings were amended with limestone, compost followed by planting of experimental trees after homogenisation. The experimental setup was of split block design with site as a blocking factor; amendment application and growth of trees as the treatment factors. After 12 months of growth, background and rhizospheric pyrite and copper tailings were sampled and their physico-chemical characteristics analysed. The Community Level Physiological Profiles (CLPP) of the same samples were determined using Biolog EcoPlate^™. The functional diversity was assessed from the Biolog data using various indices including Average Well Colour Development (AWCD), substrate richness (S) and Shannon-Wiener index (H).

Background and rhizospheric untreated pyrite and copper tailings were extremely acidic, with low organic matter content, available phosphorous, total nitrogen, and relatively higher concentrations of available heavy metals and low bacterial functional diversity. Application of amendments and growth of the tree species effectively increased the pH, organic matter content, available phosphorous, total nitrogen, growth of understory plant species, bacterial functional diversity and lowered the available concentrations of heavy metals. AWCD, bacterial species diversity and richness were higher in rhizospheres of leguminous tree species than the non leguminous Eucalyptus grandis, suggesting the suitability of the former for remediation of pyrite and copper tailings.

Keywords: efficacy, compost, restoration, bacterial functional diversity, rhizosphere, Biolog Ecoplate^™