Biochemical properties of highly mineralised and infertile soil modified by acacia and spinifex plants in northwest Queensland, Australia

Abstract

Root zone soil properties can significantly influence the establishment of revegetated plant communities and alter their development trajectories in mined landscapes, due to closely coupled biogeochemical linkages between soil and plant systems. The present study aimed to characterise physicochemical and biochemical conditions in soil colonised by slow-growing native plant species: Acacia chisholmii (C3, native leguminous shrub) and Triodia pungens (spinifex C4 grass) in Mt Isa, North-west Queensland, Australia. This is to provide the basis for engineering growth media and root zones suitable for supporting target native plant communities to be revegetated in mined landscapes under subtropical and semiarid climatic conditions. Litter chemistry, soil physicochemical properties, and microbial community structure based on phospholipid fatty acids (PLFAs) biomarker method and activities (basal respiration, net mineralisation, dehydrogenase, invertase, urease and neutral phosphatase activities) were characterised in the surface soils beneath the keystone native plant species. Results showed that soils sampled were generally infertile with low levels of total organic carbon (TOC), available nutrients and slow cycling processes with bacteria dominant microbial communities supporting the native plant species. Surface soils underneath acacia and spinifex were modified by in situ litter return, in terms of TOC, and structure and functions of microbial communities. The levels of soil microbial biomass C and N, basal respiration rate and net mineralisation rate in the acacia soil were twice as much as those in the spinifex. Microbial communities in the acacia soil had a greater fungal:bacterial ratio than in the spinifex. On this basis, growth media and root zones for revegetating native acacia-spinifex communities at local mined landscapes may be engineered by using plant organic matter remediation to supply available nutrients and to rehabilitate suitable microbial communities for in situ litter decomposition and nutrient cycling.