Physiological Responses, Growth, and Heavy Metal Accumulation of Citronella (Cymbopogon nardus Rendle. ) in Cu-Ni Mine Tailings as Affected by Soil Amendments

Abstract

This study aimed to contribute to the rehabilitation and remediation of mine tailings and heavy metal (HM) contaminated environments through phytostabilization using plants with added economic benefits such as citronella (Cymbopogon nardus Rendle.). A greenhouse pot experiment of citronella was evaluated in Cu-Ni mine tailings by monitoring its growth rate, physiological responses, and HM accumulation as affected by the application of four different soil amendments under greenhouse conditions. The treatments include T1 (control) as tailings without amendments, T2 as tailings + 10% cow manure (v/v), T3 as tailings + 10% compost (mixture of organic farm waste and manure, v/v), T4 as tailings + lime at 5 tons ha–1, T5 as tailings + lime (2x) at 10 tons ha–1, and T6 as tailings + 10% fly ash (FA) by volume. After 24 wk, soil amendments enhanced dry matter yield and increased chlorophyll content, leading to higher photosynthetic rate and rubisco activity in the leaves of citronella. These amendments reduced the availability of HM in tailings and consequently reduced its translocation to above- ground parts and the concentration in shoots. Cow manure, FA, and compost increased the total N, available P, and exchangeable K in tailings. Applications of FA, compost, lime, and cow manure significantly enhanced the survival and growth of citronella in tailings and thereby increased the potential of citronella as phytostabilization agents of Cu-Ni tailings. The high dry matter yield of citronella will produce a high volume of essential oils as an additional benefit.