TEMPERATURE AND MICROBIAL EFFECTS ON NITROGEN CYCLING AT SIMULATED MORTALITY DECOMPOSITION HOTSPOTS

Trillions of microbes reside in and on the bodies of vertebrates, making up their natural microbiome. After the host dies, many of these microbes participate in decomposition of tissues, particularly early in decay. Along with host-associated communities, environmental microbes (many concentrated in soil) also function as key decomposers. However how these two distinct communities interact to recycle carbon (C) and nitrogen (N) in soils is unclear. As a way to begin to test the role of these communities and their interactions under different environmental conditions, a series of experiments were designed to assess the contributions of soil and gut microbes to transforming nutrients in soil in a simulated decomposition scenario. The fate and transformations of C and N compounds were evaluated weekly for 6 weeks under three temperatures: 10°C, 20°C, and 30°C. Within each temperature there were 5 treatments: (1) sterile soil and live decomposition fluid; (2) live soil and sterile decomposition fluid; (3) live soil and live fluids; (4) live soil and an inorganic source of N and phosphorus; (5) control. Nitrate, ammonium, and respiration (CO₂ release) were all elevated in the 30°C treatments compared to 10°C and 20°C. In treatment 1 (host-associated microbes only), there was elevated ammonium, which persisted for the course of the experiment, with no change in nitrate over time. In contrast, treatments 3 (host- and soil microbes) and 4 (soil microbes plus inorganic N and P) exhibited a drawdown of ammonia and increasing nitrate over time and with increasing temperature. This suggests that native soil microbes are key to nitrate production and host communities contribute only minimally to nitrification. The release of CO₂ exhibited a 2 week lag from the introduction of C and N (and P) sources, suggesting that native soil microbes have a delayed response to a pulsed nutrient event. Combined with observations from decay experiments conducted in the field, we can begin to constrain how host-associated and soil-derived microbes interact to cycle nutrients at carrion hotspots.