Can litterfall input mitigate the adverse effects of high-severity wildfires on soil functions in temperate forest ecosystems?

Global climate warming is propelling an increase in forest wildfires and relevant ecosystem degradation. How the legacy effect of wildfires will act on soil multifunctions and whether litterfall, especially prominent in terms of biotically induced functions, will contribute most to the recovery patterns after wildfires remain largely unexplored. To fill these gaps in knowledge, comprehensive soil function assessments were conducted using 38 soil indicators, covering five functional groups, namely, soil buffering and filtration, water conservation, carbon storage, nutrient cycling and microbial habitat. We tracked their shifts and the overall soil multifunctionality in paired burned and unburned sites during the mid-growing season from 2019 to 2021 (i.e., the first three years following high-severity wildfires) over the Pinus tabuliformis plantation of North China. The responses of the trade-offs and synergies between soil functions to wildfires, year and their interaction were illuminated. We further determined 18 biotic (i.e., understory plant and litterfall) and abiotic (i.e., soil temperature) variables to explain the mechanism of variations in soil multifunction. Results showed that soil multifunctionality and most single functions of the burned site were coherently less than those of the unburned site, whereas the opposite pattern was found for the soil microbial habitat, which is particularly significant in the first post-wildfire growing season. Although mutual benefit and win–win results were the melody of soil multifunction, trade-offs/synergies among functions in the burned site were dampened over time. Plant attributions explained 60.6% of the variation in soil water conservation, whereas they and litterfall properties played as the main direct pathways to wildfire impacts on soil buffering and filtration. We highlighted the tremendous effect of litterfall mass on soil multifunctionality as well as carbon storage and nutrient cycling independent function, largely overpassing those of plant attributions and soil temperature. These findings unfold the potential of litterfall input as a suitable early intervention for facilitating soil functioning after wildfires. Moreover, the strong interactions of wildfires and time shed lights on the requirement for long-term frameworks concurrently considering biotic and abiotic factors to understand the overall situation of wildfire influences on ecological processes.