Abstract
Shark Bay Salt (SBS) has been operating at Useless Loop and Useless Inlet since 1965 and is managed separately from the surrounding Shark Bay World Heritage Property. The area is subject to both temperate and semi-desert climate patterns and is a major transition zone of the South West and Eremaean Biogeographic regions which are dominated by Eucalyptus and Acacia species respectively. Within the SBS lease area, the development of the salt production ponds and the construction of the site infrastructure resulted in excavation of borrow pits at numerous sites. Although the majority of the borrow pits were decommissioned 15 years ago, many remain in a highly disturbed state when compared to the surrounding undisturbed areas.
Legumes often are pioneer species in disturbed sites, in part due to their ability to form symbioses with nitrogen fixing root nodule bacteria (RNB) and often are major contributors to the nitrogen economy of their plant communities (Allen and Allen 1981, Beadle 1964 ). The key overstorey leguminous species within the SBS lease area are Acacia ligulata and Acacia tetragonophylla, and to a lesser extent Acacia rostellifera and Templetonia retusa. These species associate with understorey annual and perennial species to form 'fertility islands'. In a semi-arid Mediterranean area, these 'islands' are sites of high biological activity (Caravaca et al. 2003). Removal of native legumes and long term disturbance to an environment not only alters the chemical and physical properties of the soil but often results in the decline or absence of RNB in the soils (Thrall et al. 2001 ), which may be a contributing factor to the lack of recruitment of flora from the surrounding undisturbed areas.
Aims of this study are to: 1) determine if borrow pit mining has had a detrimental effect on numbers of RNB present when compared to undisturbed sites and 2) select inocula substrates suitable to maintain the viability in pit site conditions of isolated RNB that effectively fix nitrogen with A. tetragonophylla and A. ligulata.