The stoichiometric legacy after fire: multi-element shifts and arthropod community filtering in a subtropical grassland

Abstract Background Fire is a disturbance that alters nutrient cycling, but its legacy is often reduced to shifts in carbon (C), nitrogen (N), and phosphorus (P). This C:N:P paradigm overlooks the vast suite of other elements critical to decomposer organisms. Post-fire changes in the abiotic environment—especially when interacting with co-occurring stressors such as ultraviolet (UV) radiation—may reorganize the entire multi-element stoichiometric network within litter, yet the direct implications for arthropod decomposer communities remain largely unknown. Results In a 469-day factorial field experiment in a subtropical pastureland, we imposed prescribed burn and UV radiation treatments on litterbags. By quantifying 33 elemental ratios of litter, we revealed that abiotic environment change post fire acted as a reductive force, significantly decreasing 20 ratios (e.g., ln C:Fe by 6.89%, ln N:Fe by 8.76%) and enriching the litter with metals. In contrast, UV radiation decoupled potassium from litter, increasing ratios like K:P and K:Na. These reconfigured elemental landscapes of litter directly filtered the arthropod community, with diversity showing strong negative correlations with metal N, P and K constraints (e.g., N:Mn, N:Fe). Conclusions We demonstrate that post-fire abiotic environmental change and UV rewire litter stoichiometry towards distinct, metal-enriched, and potassium-decoupled states. This multi-element network perspective moves beyond the C:N:P paradigm to reveal a powerful mechanism through which disturbances shape decomposer communities. Monitoring these stoichiometric networks provides a predictive framework for assessing the ecological legacy of fire in a changing world.