Effect of climate change on plant-microbe interactions in sub-alpine ecosystems

Abstract

Climate change is rapidly altering high-elevation ecosystems, where increases in temperature and shifts in rainfall patterns are expected to strongly influence both plant communities and the soil environments that support them. Microbial communities play a central role in these systems by regulating nutrient cycling, supporting plant growth, and maintaining ecosystem stability. However, how climate stressors especially multiple climate stressors interact to reshape these microbial communities and how such changes influence plant-microbe interactions remain poorly understood in this high-elevation ecosystem. My thesis investigates how warming and drought influence soil- and root-associated microbial communities in Australian sub-alpine grasslands, and how these changes affect plant performance and root colonisation. A set of field-based manipulations and controlled greenhouse experiments were used to examine microbial diversity, community structure, functional potential and plant-microbe interactions. Across the thesis, combined warming and drought consistently imposed the strongest impacts on both soil- and root-associated microbial communities and plant performance, indicating that interacting climatic stressors amplify ecological disruption in sub-alpine ecosystems. Among individual stressors, warming generally exerted broader and more consistent negative effects than drought alone, particularly for fungal and arbuscular mycorrhizal fungal (AMF) communities. In contrast, drought effects were often more variable and appeared especially important for bacterial community restructuring. Moreover, prolonged climatic stress generally reduced symbiotic fungal groups while favouring saprotrophic, opportunistic, and stress-associated taxa across both soil- and root-associated communities. These shifts suggest a potential weakening of beneficial plant-microbe associations under climatic stress, which may increase plant vulnerability to environmental stress and disease pressure under future climate change. Collectively, climate stress led to consistent but group-specific changes in soil microbial communities, with combined warming and drought producing the strongest effects. These changes extended beyond reductions in diversity to altered microbial interactions and functional potential, indicating that climate stress reshapes not only the composition of microbial communities but also their ecological roles. However, plant responses to warming and drought in control growth chambers were highly species-dependent and links between root fungal community changes and plant performance were often weak, suggesting that above and belowground responses do not always change in parallel. Finally, a field-based transplant experiment demonstrated that climate stress and host species reshapes root-associated fungal communities during plant establishment by altering which taxa successfully colonise plant roots. Overall, this thesis demonstrates that climate change reshapes soil- and root- microbiomes in group-specific ways, influencing not only microbial diversity and function but also the assembly of root-associated communities. These findings provide new insights into ecosystem responses to climate change and have important implications for predicting ecosystem resilience and informing restoration strategies in sub-alpine systems. Show more