Article from Sashini Perera & Michelle R. Leishman
contact email: bulathsinhalage-sashini-d.p [at] students.mq.edu [dot] au
School of Natural Sciences and Centre for Smart Green Cities, Macquarie University, North Ryde, NSW 2109, Australia
Urban green spaces—such as bushland remnants, street trees, parks, and gardens—offer essential benefits to both people and biodiversity. However, they often face challenges like limited space, poor soil quality, and low water availability, which are being intensified by climate change. As cities experience rising temperatures and more frequent extreme weather events, it is crucial to improve the resilience of these green spaces to ensure their continued function and value.
To reduce plant water stress in urban environments, soil modifications like biochar and microbial inoculants can improve plant-water relationships. While individual treatments are well-studied, little is known about how they work together. Exploring these interactions could lead to more effective strategies for enhancing the resilience of urban green spaces to climate change.
Our research aimed to improve the resilience of urban tree species to climate change by developing strategies that help native trees thrive in harsh conditions. Beyond selecting climate-resilient species, it explored how soil management—particularly the use of biochar and microbial inoculants—can boost water retention, nutrient availability, and soil health in hot, water-limited environments.
In a glasshouse experiment, we tested four tree species—Allocasuarina littoralis, Casuarina cunninghamiana, Corymbia maculata, and Eucalyptus botryoides—to assess whether soil additives could improve plant performance under low moisture conditions. While water stress significantly reduced plant growth across all species, soil amendments did not counteract the decline in biomass. However, biochar improved soil water retention and reduced leaf necrosis, indicating its potential as a cost-effective tool to support urban forest resilience. Well-watered soils showed higher nitrogen levels than water-stressed soils, while biochar application led to an increase in soil carbon content. However, neither soil treatments nor water availability had a significant impact on the chemical concentrations in the leaves.
Figure 1) Well-watered soil had higher levels of Nitrogen compared to the water-stressed soil. Biochar increased the carbon content in soil.
(B: Biochar, M: Microbial additive, BM: Biochar + Microbial additive and N-No additive).
Figure 2) No significant effect from soil treatments or water treatments for the chemical concentrations in leaves.
(B: Biochar, M: Microbial additive, BM: Biochar + Microbial additive and N-No additive).
While soil amendments like biochar can improve water retention and support plant resilience under dry conditions, they may have unintended negative effects in wetter scenarios. During periods of extreme rainfall, increased soil moisture retention can lead to waterlogging, which reduces oxygen availability to roots and may cause root rot or stunted growth. These conditions can also disrupt nutrient dynamics, leading to leaching or imbalances that harm plant health. Therefore, the use of soil modifications should be carefully tailored to site-specific factors such as climate, soil type, and drainage capacity, with a balanced approach that considers both benefits and potential trade-offs.
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