Regional postdeforestation weathering feedback drove diachronous C–S cycle perturbations during the end-Permian crisis

The Permian-Triassic (P-Tr) transition (~252 Ma) witnessed Earth's most severe biocrisis, which has long been linked to Siberian Traps volcanism and associated environmental upheaval. Major perturbation of the global carbon (C) and sulfur (S) cycles is mainly inferred from marine δ¹³C and δ³⁴S records, whereas few existing terrestrial records link δ³⁴S fluctuations to widespread dispersal and fallout of volcanogenic sulfate aerosols. Mounting evidence, however, reveals that the collapse of P-Tr terrestrial ecosystems was diachronous, questioning a hypothesized globally synchronous common forcing. Here, we present records of pyritic multiple-S isotopes (δ³⁴S_py and Δ³³S) and bulk organic δ¹³C for a paleotropical peatland drill core (HK-1) from Southwest China. The δ³⁴S_py variations define three distinct phases with a notable decline in δ³⁴S_py across the P-Tr transition, suggesting substantially elevated terrestrial sulfate influx coincident with major carbon cycle perturbation. Notably, overall small positive Δ³³S values (+0.01 to +0.12‰) rule out a dominant role for stratospheric sulfates. Collectively, the observed changes in δ¹³C_org, δ³⁴S_py, and Δ³³S support catastrophic collapse of the Cathaysian Flora leading to intensified weathering and sulfate release. This inferred event, slightly after the P-Tr marine extinction, postdates by several 100-ky terrestrial floral collapse and perturbation of the C-S cycles documented in the high-latitude Sydney Basin. Cross-latitudinal diachroneity of terrestrial ecosystem collapse and consequent C-S perturbation challenges the hypothesis of a single, global volcanic driver. Rather, regional deforestation and its cascading effects overprinted on the global perturbations of biogeochemical cycles emerge here as critical factors shaping Earth's largest recorded crisis.