The effects of sterilisation on abiotic soil properties and the challenge this poses to untangling the influence of abiotic and biotic soil variables on plant growth

To separate the effects of the abiotic and biotic soil components on plant growth, researchers can compare plants grown in sterilised and unsterilised soil (unsterilised soil approach). However, using this approach can be problematic if the abiotic component of the soil is affected by the sterilisation treatment, which is often the case. We aimed to determine how often this approach is used by plant-soil interaction studies and demonstrate how it can impact plant growth. We reviewed the relevant literature to determine how often the unsterilised soil approach is used and whether the studies that use it acknowledge the ‘soil sterilisation’ caveat. We then conducted a glasshouse experiment to demonstrate the effect that soil sterilisation has on selected soil nutrients and consequently on plant growth. Our literature review revealed that of the studies that used the unsterilised soil approach, only 23% measured and reported soil nitrogen or phosphorus before and after sterilisation, with 50% of these reporting a change in one or both nutrients. We then showed that the growth of our study species, Eucalyptus saligna, was greater when grown in sterilised soils compared to unsterilised soils. Interestingly, there was a strong positive relationship between the change in ammonium nitrogen and E. saligna growth between the sterilised and unsterilised soils. Given our findings, we advocate that studies that use the unsterilised soil approach should measure the abiotic soil properties before and after sterilisation and if differences are found, these studies should use the inoculation approach instead.