Tropical Deforestation, Seasonal Drought and Decline of Chemical Weathering During the Permian–triassic Transition in Southwestern China

Tropical rainforests are vital biological regulators of global climate, but their vulnerability to catastrophic environmental upheaval is often obscured by the vastness of the geological record. During the end-Permian terrestrial crisis, the demise of the tropical Gigantopteris flora in southwestern China, a key region in the eastern Tethys that preserves exceptional tropical terrestrial records, marked a pivotal breakdown in terrestrial feedbacks, specifically through a substantial decline in chemical weathering. Despite its significance, the temporal coupling and causal relationships between this floral turnover, climatic shifts, and weathering response remain poorly understood. Here, we present a high-resolution reconstruction of sporomorph assemblages, palaeoclimatic indicators, and chemical weathering intensity across the Permian–Triassic transition in southwestern China in the eastern Tethys. Our results document that the region experienced two successive phases of floral crisis. The first phase of crisis involved the collapse of pteridophyte-dominated rainforests, evidenced by a sharp decline in wetland taxa. This was followed by a second phase of crisis marked by the demise of previously thriving isoetalean herbaceous communities. These floral changes were closely linked to a progressive shift in climate, characterized by intensifying seasonal drought, as indicated by increased wildfire activity and the expansion of xerophytic vegetation. Notably, chemical weathering did not decline synchronously with the first phase of initial rainforest loss but remained elevated until the subsequent loss of isoetaleans under enhanced aridity, after which it underwent a marked and prolonged reduction that persisted throughout the Early Triassic. The two-phase floral crisis, climatic fluctuations, and the decline in chemical weathering underscore the intricate feedback loops between vegetation, climate, and weathering, highlighting the need to refine mechanistic representations of these processes in Earth system models. This study was supported by the National Key Research and Development Project of China (Grant No. 2024YFF08081100), the National Natural Science Foundation of China (grants 420305113, 42472021, 42172031) and the China Postdoctoral Science Foundation (2023 M733298). We also thank Yao Wang for assistance in field sampling and palynological preparation. We are grateful to Christopher R. Fielding and Elke Schneebeli for their time and meticulous evaluations. Their rigorous and thoughtful reviews significantly strengthened the clarity and scientific impact of this study.