The Role of Plant Diversity in the Soil Aggregate Stability of a Degraded Coal Mine

The function of mine spoil following restoration depends on the development of soil aggregation. Two models may contribute to consideration of how spoil may be restored: the hierarchical model and the interdependence model. This study examined the relationship between plant diversity and water stable aggregate in mine spoil. Four plant species Dodonaea viscosa (Jacq), Pittosporum phillyraeoides DC, Hymenosporum flavum (Hook) F. Muell, and Pandorea pandorana (Andrew Steenis) inoculated with eight different Arbuscular mycorrhizal (AM) fungi were either grown as a single species or a mixture of all species in pots containing mine spoil amended with 18% compost. Soil aggregation was measured as mean weight diameter (MWD) and organic carbon was determined after 12 months. Aggregation of spoil from under the mixed plant treatment was in the middle of the range for single species, for overall MWD and weight of each of the water-stable aggregate fractions. MWD of soil under P. phillyraeoides was higher than for all other single plant species and plant mixture. Organic carbon in the water-stable micro-aggregate sized fraction was greater in all planted than the unplanted treatment. The mean soil carbon concentration of P. pandorana was higher than all other single plant treatments and plant mixture. The study suggests that the development of aggregation of mine spoil amended with compost is independent of plant diversity.