Evidence has suggested that for certain contaminants to be degraded, a specific consortium of microorganisms must be present within the root zone (Anderson and Walton, 1995). Microorganisms have been known to reduce the phytotoxicity of contaminants to the point where plants can grow in adverse soil conditions without showing toxicity symptoms (Raskin and Ensley, 2000). As a result, other non – phytotoxic contaminants are also degraded. Anderson and Walton (1995) have suggested that the external degradation of contaminants by microorganisms in the rhizosphere is a major factor which
enhances plant adaptations to contaminated environments. Microorganisms increase the bio-availability of contaminants for uptake through plant roots. This is the case with many phytoremediative plants including Vetiver (Mukhopadhyay et al., 2010).
Rhizosphere bacterial communities play a leading role in contaminant degradation for three reasons. Firstly, they have a high abundance which influences the degradation of more xenobiotic contaminants (Anderson and Walton, 1995). Secondly, diversity of bacterial species when acting together is known to create catabolic pathways which are essential in phytoremediation (Labana, Singh, Basu, Pandey and Jain, 2005). Thirdly, the root zone has been known to contribute to microbial diversity with gram – negative bacteria being dominant (Kramer, 2010). These microbial associations are promoted by the release of exudates from roots. Most phytoremediation projects have used a limited number of species especially members of the Poaceae (Truong et al., 2008). Other commonly used families are the Fabaceae, and Silicaceae (willows) (USEPA, 2006).
2.13 Other Uses of Vetiver
Beside the use of Vetiver for land and wastewater remediation, roots produce essential oil used in the cosmetic industry. The aroma of this essential oil is heavy and extremely persistent, and therefore roots are put in sachets among clothes to preserve them, or when distilled, oil is used in perfumes, deodorants and soap (Chomchalow, 2003). The roots are traditionally used in disinfecting drinking water giving a pleasant taste and a resultant calming effect. They are also used as a natural pest control, preventing homes from insects and snakes (Juliard, 2003). These properties have been reportedly influenced by the presence of essential oils (vetivenols and zizanols) in the roots (Chamchalow, 2003). In traditional medicine, a stimulant drink is made from fresh roots in India and is also used as an anti-helminth (Cull et al., 2000). It is often referred to as Mecca in Mali, due to its well-known healthcare potentials (Juliard, 2003). Young cut leaves of Vetiver can be used as fodder for cattle and goats, whereas dried leaves are used in making brooms or for thatching of huts. Handicraft products such as hats, bags, ropes, baskets and other useful items are also made with dried Vetiver leaves (Goudiaby and Diatt, 2003).
In Nigeria, Senegal and Mali, Vetiver is often referred to as “the gift of nature”. This name is attributed to its use in settling land disputes because when planted (in a boundary), it becomes very difficult to uproot. The hollowed stem (culm) is cut into a writing quilt and used to copy religious books (Juliard, 2003). This may be connected with the reason why according to Goundiaby and Diatt (2003) it is called Jema (mosque in Arabic) in Kano, Nigeria.
No comments:
Post a Comment