Heavy metal accumulation characteristics of Nepalese alder (Alnus nepalensis) growing in a lead-zinc spoil heap, Yunnan, south-western China

Abstract

© iForest -Biogeosciences and Forestry IntroductionContamination of soil with zinc, lead and cadmium due to residues from metalliferous mining, smelting and other anthropic activities has attracted considerable attention in the past decade (Zhao et al. 2003). Because of the high toxicity of heavy metals (HMs) and their undegradable nature, metal pollution of soils has become one of the most serious environmental problems (Lee et al. 2009). In addition, heavy metals can be transferred to the food chain from the soil and seriously affect human health . First investigated by Chaney in 1983 , phytoremediation is a promising, ecologically-friendly approach to the remediation of contaminated soil using plants to remove toxic elements from the environment or render them non-toxic (Salt et al. 1998, Suresh & Ravishankar 2004. However, most plants are sensitive to excessive HMs in soil. In nature, only a small fraction of plants that exhibit metal tolerance or super-accumulative capacity (hyperaccumulators) can survive in toxic metal-contaminated soils, and the majority are herbaceous species with small biomasses (Sarma 2011). Woody plants or trees with developed root systems and large biomasses are especially attractive for revegetation and phytoremediation in metal-polluted sites (Lee et al. 2009, Capuana 2013. Additionally, exploring native plants with phytoremediation potential is a particularly important strategy, as indigenous plants are often more dependant in terms of survival, growth and reproduction under environmental stress than exotic plants (Yoon et al. 2006).Native to Pakistan, eastern Nepal, Bhutan, northern India, south-western China, upper Myanmar and parts of Indochina, A.nepalensis is a multipurpose alder species. Characterized by a series of merits such as fast growth and nitrogen fixation, its uses include commercial timber production of moderately soft wood and charcoal feedstock. Moreover, A. nepalensis is a chief associate in various commercial timber plantations, where it not only helps to raise the nitrogen levels of fields but also acts as a pioneer species on denuded habitats with freshly exposed soils, or rocky and eroded slopes in subtropical-totemperate belts of the Himalaya (Sharma & Ambasht 1984). Several other Alnus species have been surveyed to evaluate their phytoremediation potential for metal contaminated soils. For example, Rosselli et al. (2003) found that Alnus incana could be considered as an excluder of Zn, Cd and Cu. Mertens et al. (2004) found that Alnus glutinosa showed low foliar heavy metal concentrations and might therefore be suitable for phytostabilization purposes on polluted sites. Lee et al. (2009) also reported that Alnus hirsuta was a better candidate than Alnus firma for phytoremediation of HM-contaminated soils. However, there is no information about the potential of Alnus nepalensis to remediate Zn-, Pb-and Cd-contaminated soils.In the present study, the metal accumulation capacity of A. nepalensis growing in a lead and zinc mining spoil heap in Lancang county o...

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