Dryland soil mycobiome response to precipitation variability depends on host plant association

Nicolas Louw, Plant Biology, University of Georgia, Athens, GA, Osvaldo Sala, School of Sustainability, Arizona State University, Tempe, AZ, Laureano Gherardi, Global Drylands Center, Tempe, AZ and Anny Chung, University of Georgia

Background/Question/Methods
Climate change is causing shifts in the global water cycle, resulting in increased precipitation variability. These effects will be most pronounced in drylands, which cover 40% of the Earth’s terrestrial surface. Results from previous work show that increased precipitation variability decreased grass cover, increased shrub cover and overall, decreased aboveground net primary productivity. However, the effects on belowground communities, and how that relates to aboveground responses, remain unknown. The objective of this study was to evaluate how the increase in precipitation variability influenced plant-associated soil fungi. We characterized soil mycobiome composition from different precipitation treatments and host plants, or microsites, collected from a long-term field study at Jornada Basin LTER. This field study consisted of four levels of increased interannual precipitation variability (-/+50%, +/-50%, -/+80% and +/-80%) that kept the same mean as ambient precipitation (control) over 10 years. From these experimental plots, we collected soil samples underneath three different microsites that included bare soil, grass, and shrubs in 2013 and 2019. Next, we extracted DNA, sequenced samples using next generation sequencing techniques, assigned fungi to operational taxonomic units, and grouped fungi according to functional guilds.
Results/Conclusions
Soil fungal Shannon diversity differed significantly by microsite (F2,238= 18.38, P < 0.001). Specifically, soil fungal diversity was highest underneath grasses, followed by bare soil, and least diverse underneath shrubs. The effects of increased precipitation variability and microsite on soil fungal diversity also significantly depended on year (interaction F4,238= 6.25, P < 0.001 and F2,238= 4.50, P= 0.01, respectively). Soils treated with -/+ 50% precipitation variability, decreased in mycobiome diversity from 2013 to 2019. Conversely, soils treated with ambient precipitation, increased in mycobiome diversity from 2013 to 2019. Across all precipitation treatments, soil mycobiome diversity increased in bare ground from 2013 to 2019. Soil fungal community composition differed significantly by year, precipitation variability, and microsite, with significant microsite by year and precipitation variability by year interactions. The majority (85%) of taxa characterized from samples consisted of Ascomycota. However, results from indicator species analyses show that different phyla responded specifically by treatments. For example, Basidiomycota were disproportionately represented in higher precipitation variability treatments versus ambient precipitation, and underneath shrubs than grasses or bare soil. Results from this experiment show that the soil mycobiome changes in response to increased precipitation variability over time, and that these responses vary significantly by host plant association.