Scavengers and vegetation regulate soil microbial and biochemical shifts in response to carrion decomposition

Animal carcasses represent localized nutrient pulses that can influence soil microbial communities and biogeochemical processes, particularly in nutrient-depleted soils. However, how biotic factors (e.g., scavenger activity, carcass type and vegetation cover) shape these belowground effects remains poorly understood. Here, we experimentally assessed changes in soil microbial community structure and activity following carrion decomposition and their modulation by these biotic drivers in a Mediterranean dryland. We deployed 10 red fox ( Vulpes vulpes ) and 10 aoudad ( Ammotragus lervia ) carcasses in Sierra Espuña Regional Park (Murcia, Spain) and measured soil microbial community composition (phospholipid fatty acid profiles), activity (basal respiration, microbial biomass carbon and extracellular enzymatic activities) and physicochemical properties before deployment and five months later. Scavenger activity was assessed with camera traps and vegetation cover was recorded for each carcass. Carrion deposition significantly altered soil conditions, decreasing pH (−2.5%) and increasing electrical conductivity (+82.2%) and phosphorus availability (+449.7%). Microbial communities shifted markedly, with Gram-negative bacteria increasing importantly (+246.7%) and Gram-positive groups declining (−28.6%), while total microbial biomass and activity showed limited changes. These responses were strongly modulated by biotic factors: carcasses consumed by more scavenger species showed dampened microbial responses, whereas denser vegetation cover enhanced microbial responses. Carcass type also modulated microbial responses, with mesocarnivore carcasses inducing stronger shifts relative to their mass, likely due to longer persistence and differential scavenging dynamics. Our findings demonstrate that carrion effects on soils depend not only on nutrient inputs but also on large-scale ecological processes regulating carcass persistence. By linking scavenger activity and vegetation structure with microbial responses, our results highlight carrion as a key interface coupling above- and belowground processes, ultimately shaping microbial heterogeneity and regulating zoogeochemical nutrient pathways in dryland ecosystems. Transfers of biomass and nutrients from carcasses to soil (dark brown arrows) drive shifts in microbial community composition and physicochemical properties during decomposition in soils collected before (PRE) and five months after carcass deployment (POST). These effects are modulated by aboveground biotic factors (white dashed arrows). Scavengers consume and disperse carrion biomass, regulating carcass–soil interaction time and reducing the nutrient influx to soils. Thus, carcasses consumed by richer scavenger communities show weaker microbial shifts. Additionally, scavenging consumption patterns differ depending on carcass identity; carnivore carcasses remain longer in the environment and trigger relatively stronger microbial shifts. Moreover, carcasses under thicker vegetation cover are related to wider shifts in soil microbial communities. Significant effects are shown with asterisks. • Carrion decomposition drives microbial and biochemical shifts in dryland soils. • Carcass inputs shift soil communities from GP to GN bacterial dominance. • Scavengers dampen soil responses by reducing carcass-soil interaction time. • Vegetation cover enhances shifts in soil variables. • Maintaining carrion biotic interactions promotes soil microbial heterogeneity.