Drought and mycorrhizal inoculation affect growth and morphology of Australian stormwater biofilter plants

This study evaluated the effect of mycorrhizal inoculation on six common Australian biofilter plant species using a pot experiment. We divided 120 pots planted with six common biofilter species into four treatments: control water-deficit, inoculated water-deficit, control well-watered, and inoculated well-watered. Inoculated treatments were inoculated with a commercially available blend of arbuscular mycorrhizal fungi spores. While well-watered pots were watered to pot capacity daily, water-deficit pots were subjected to a simulated drought that lasted six weeks until harvesting. All plants inoculated with arbuscular mycorrhizal fungi developed greater total root surface area, plant biomass, and plant relative growth rate. Which are associated with better stormwater nutrient removal. Mycorrhizal inoculation also increased the average root diameter, total length, and surface area of thick roots (diameter > 1 mm) of six species, which are essential to maintain the infiltration rates and hydraulic functions of biofilter systems. Moreover, an increase in shoot biomass following inoculation was also observed across six species, potentially contributing to higher water loss and stormwater volume reduction. Although the water-deficit condition greatly limited the effects of mycorrhizal inoculation on other morphological traits, we still observed the benefits of inoculation on total root length and surface area in well-watered J. pallidus and C. appressa. As drought stress imposes limitations on the effects of inoculation, we recommend inoculation should be carried out in advantageous times, such as during wet periods before the drought season for the optimal colonization and plant biomass and morphological responses. Additionally, selecting mycorrhizae-responsive species like C. appressa, J. pallidus, and G. sieberiana can result in favorable outcomes.