Biochar, but not soil microbial additives, increase the resilience of urban plant species to low water availability

Abstract

Impervious surfaces that characterise urban areas can make them harsh, water-limited places for plants to grow. To help alleviate plant stress under these challenging drought conditions, a range of soil additives can be utilised. Although well-studied individually, our understanding of the interaction between different soil additives in alleviating drought stress in urban areas is rudimentary. The aim of this study was to (1) assess the growth of urban horticultural plant species under drought stress and (2) determine whether drought stress in these species is alleviated by the use of soil additives, both individually and in combination. We grew six plant species (three trees, three graminoids) commonly planted in Australian urban areas under two watering regimes (drought-stressed, well-watered) and four soil additive treatments (no additive, microbial additive only, biochar only, microbial additive and biochar), and assessed their performance. We found that drought stress significantly reduced the growth of the six study species. Surprisingly, this decrease in growth was not reduced with the use of soil additives, despite biochar increasing soil water content and mycorrhizal colonisation when used in combination with the microbial additive. However, the addition of biochar significantly delayed the visual onset of drought stress across all species. Our results show that soil additives can be used as a cost-effective management strategy to increase plant resilience to drought stress in urban areas.