Bioturbation by bandicoots facilitates seedling growth by altering soil properties

Abstract

Abstract Animals that forage for food via bioturbation can alter their habitat, influencing soil turnover, nutrient cycling and seedling recruitment, effectively acting as ecosystem engineers. Many digging mammals forage for food by digging small pits and creating spoil heaps with the discarded soil. We examined how small‐scale bioturbation, created by the foraging actions of an ecosystem engineer, can alter soil nutrients and subsequently improve growth of plants. We investigated the microbial and chemical properties of soil disturbed by the foraging of an Australian marsupial bandicoot, quenda (Isoodon fusciventer). Soil was collected from the base of 20 recent foraging pits (pit), the associated spoil heaps (spoil) and adjacent undisturbed soil (control) and analysed for nutrients (phosphorus, potassium, sulphur, organic carbon and conductivity) and microbial activity. Soil cores were collected from the same locations and seeds of the dominant canopy species, tuart (Eucalyptus gomphocephala), added to the soil under glasshouse conditions. The growth of seedlings was measured (height, maximum growth, basal stem width, shoot and root biomass) over a 4‐month period and arbuscular mycorrhizae (AM) fungi colonisation rates of seedling roots investigated. Soil from the spoil heaps had the greatest levels of conductivity and potassium. Both the spoil and undisturbed soil had greater amounts of microbial activity and organic carbon. In contrast, the pits had less nutrients and microbial activity. Seedlings grown in spoil soil were taller, heavier, with thicker stems and grew at a faster rate than seedlings in the pit or control soil. Colonisation with AM fungi was greatest for seedlings grown in pit soil. The best predictors of seedling growth were greater amounts of potassium, electrical conductivity and microbial activity. The best predictor of higher colonisation rates of AM fungi was less phosphorus. Bioturbation by ecosystem engineers, like quenda, can alter soil nutrients and microbial activity, facilitating seedling growth. We propose this may be caused by enhanced litter decomposition beneath the discarded spoil heaps. As the majority of Australian digging mammals are threatened, with many suffering substantial population and range contractions, the loss of these species will have long‐term impacts on ecosystem processes. A plain language summary is available for this article.