COS 269-2 - Dung Beetles, Soil Microbes, and Soil Nutrients in California's Central Coast

Abstract:

Background: Soil organic carbon content (SOC) in pasturelands is mediated by the soil microbial community, which is, in turn, largely shaped by influxes of nutrients and the soil arthropod community. One such arthropod, the tunneling dung beetle Onthophagus taurus, incorporates animal dung into the soil, influencing the soil microbial community and nutrient cycling. In two studies in 2020 and 2021, we examined how the presence and abundance of the tunneling dung beetle O. taurus affects the fungal, bacterial, and archaeal community of pastureland soil in California’s Central Coast region. For two months each summer, we conducted an in situ enclosure experiment that varied dung beetle abundance (no beetles, low abundance, high abundance). We collected soil samples at the start, middle, and end of the experiments, and then and then used eDNA metabarcoding of the 16S and ITS1 loci, and PERMANOVA analysis of the resulting sequences to examine for shifts in fungal, bacterial, and archaeal communities over time in the different dung beetle treatments. In 2020, we focused on the surface soil (0-1 cm) and in 2021, we focused on deeper soil samples (0-10 cm, the depth at which dung beetles burrow), but also took limited surface soil samples.



Results: In 2020, we found that dung beetle presence and abundance had significant effects on the soil microbial community in surface soil samples. Specifically, dung beetle abundance significantly altered the soil bacterial archaeal community (16S, F=3.973, P=0.001, R2=0.098). Likewise, dung beetle abundance also affected the soil fungal community (ITS1, F=6.155, P=0.001, R2=0.147). In 2021, we found that dung beetle presence had a weak but significant effect on the deeper soil fungal community when considering dung beetle treatment, day, and ranch as factors (F=1.605, P=0.031, R2=0.014); however, we did not observe any effects of dung beetles on the soil bacterial/archaeal community (F=1.443, P=0.126, R2=0.012). Yet dung beetle presence continued to strongly and significantly influence both bacterial and fungal communities in surface samples (F=4.64, P=0.001, R2=0.224). Our results indicate that dung beetles can play important roles not only in soil aeration and nutrient cycling in pastures, but also influence soil microbial conditions. However, their effects on bacteria may be limited to surface soils.