Effects of drought on dryland soil microbial community and functional attributes

Abstract

Global circulation models predict significant changes in precipitation patterns, including more extensive periods of drought followed by heavy precipitation events. Drought is a major threat to Earth's ecosystems, impacting both above and below-ground organisms, particularly in dryland ecosystems, which are already water limited. This thesis examined the long-term effects of altered rainfall regimes on the soil microbiome in semi-arid and arid regions and associated impacts on ecosystem function. The research presented utilized six field sites in arid to semi-arid NSW and QLD, Australia, with three replicates for each rainfall treatment: increased (65% above ambient), reduced (65% below ambient), and control (ambient rainfall). The long-term study conducted from 2016-2019 revealed that as drought intensity increased, stress-tolerant microbes including Actinobacteria, Alpha-proteobacteria, Chloroflexi, and Ascomycota became more abundant, shaping the microbial communities in these ecosystems. Furthermore, soil multitrophic interactions among bacteria, fungi, protists, and nematodes, were investigated using samples collected in 2020. Interestingly, under more arid conditions, positive co-occurrence relationships among bacteria strengthened, resulting in networks dominated by oligotrophic bacteria with significant influence on the multitrophic network structure. Lastly, to understand the long-term impacts of drought and altered rainfall on microbial functions, I examined the decomposition of litter by bacteria and fungi at the same sites, during the summer of 2020 and 2021. The research revealed strong effects of rainfall treatment on litter decomposition across all sites, with some of the variation in decomposition explained by microbial taxa that became more abundant during the natural prolonged drought. Overall, throughout the study, environmental factors such as mean annual precipitation, aridity, geographic location, pH and soil C strongly determined microbial community structure and thus their associated functions. This thesis highlights the eminent threat of climate change and increasing aridity in drylands to soil communities and ecosystem functioning.

Date of Thesis submission	2023
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Uffe Nielsen (Supervisor)