79-6 Trait shifts in plant fossils predict survival in a heating Earth: simulated vegetation-climate interactions across the Triassic-Jurassic Boundary

Abstract:

Heating episodes in Earth’s past have likely acted as ecological filters for plant traits. Volcanism at the Triassic-Jurassic (T-J) boundary in the middle Mesozoic elevated atmospheric CO2 (>2000 ppm) and induced heating (GMST >24°C). Biogeographic limitation and macrofloral turnover have produced hypotheses regarding the ecology and traits of survivor taxa. For example, leaf temperature may be reduced in narrow leaves capable of transpiring in hot, dry conditions. Here, we parameterize a process-based model of ecosystem processes (i.e., paleo-BGC) using paleo-traits (functional traits measured in fossils) to test the impact of leaf width, maximum stomatal conductance (g_max), and xylem vulnerability to cavitation-induced embolism (Ψ_C). Using Paleo-BGC, trait combinations are tested in the climate space of the T-J, based on global climate model simulations (HadCM-3B). We test whether water-use trait coordination (1) limits forest cover and (2) corresponds with the pattern of community turnover observed at classic T-J sites. We compare the maximum temperatures of T-J leaves at several CO₂ levels with the thermal tolerance of forest trees from neo-botany. Process-based simulations parameterized using fossils show where, how, and why plants survived or went extinct during deep-time heating episodes, and allow hypothesis testing against the fossil record—enabling better vegetation projections under different anthropogenic CO₂ emissions scenarios.

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