Plant species modulate wildfire effects on soil phosphorus fractions in alpine forest of Eastern Tibetan Plateau

Abstract

Global wildfires occurring with ever escalating frequency and intensity profoundly disrupt soil phosphorus (P) cycling in forest ecosystems. The impact of plant species on post-fire soil P transformation, particularly in alpine forests, remains largely unexplored. This study addressed this gap by investigating both bulk soils (BS) and root-zone soils (RS) across three plant species (shrub: Sophora davidii and Quercus aquifolioides, tree: Pinus densata) in the alpine forest of the eastern Tibetan Plateau, three years after a wildfire event. We examined variations in soil P fractions under varying wildfire intensities using the modified Hedley sequential extraction method. Compared to unburned soils, the burned soils exhibited significantly reduced organic P (P_o) but increased inorganic P (P_i) concentrations in BS. However, both P_i and P_o concentrations decreased in the burned RS, particularly for S. davidii and P. densata, indicating the effects of biological P utilization. The increased specific phosphatase activity and the ratio of carbon to P_o suggested increased P limitation in the post-fire environment. Notably, the N₂-fixer S. davidii primarily reduced labile P fractions through direct plant P uptake, while conifer tree species P. densata tended to deplete all extractable P fractions, probably through diverse P utilization strategies. Conversely, Q. aquifolioides did not significantly alter soil P fractions, likely due to its fire-resistant properties. These species-dependent impacts on post-fire P fractions were further corroborated by their distinct influences on soil and microbial traits. Our findings underscore the critical roles of functional-specific plant species in post-fire soil P dynamics in alpine forests, with conifer trees exhibiting the best P mining and utilization capacity.