Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event

Abstract

Climate change is likely to have altered the ecological functioning of past ecosystems, and is likely to alter functioning in the future; however, the magnitude and direction of such changes are difficult to predict. Here we use a deep-time case study to evaluate the impact of a well-constrained CO-induced global warming event on the ecological functioning of dominant plant communities. We use leaf mass per area (LMA), a widely used trait in modern plant ecology, to infer the palaeoecological strategy of fossil plant taxa. We show that palaeo-LMA can be inferred from fossil leaf cuticles based on a tight relationship between LMA and cuticle thickness observed among extant gymnosperms. Application of this new palaeo-LMA proxy to fossil gymnosperms from East Greenland reveals significant shifts in the dominant ecological strategies of vegetation found across the Triassic-Jurassic transition. Late Triassic forests, dominated by low-LMA taxa with inferred high transpiration rates and short leaf lifespans, were replaced in the Early Jurassic by forests dominated by high-LMA taxa that were likely to have slower metabolic rates. We suggest that extreme CO-induced global warming selected for taxa with high LMA associated with a stress-tolerant strategy and that adaptive plasticity in leaf functional traits such as LMA contributed to post-warming ecological success.

Extinction risk and threats to plants and fungi

“…Plants have been considered more robust to the mass extinctions documented in the fossil record (e.g., driven by massive volcanic activity and/or bolide impact) due to their life-history traits, such as seed-dormancy, leafdropping, and hybridization (Traverse, 1988). Shifts in leaf-traits across mass extinction boundaries clearly show plant responses to these events, revealing traits associated with taxa that fared better across the end-Cretaceous extinction c. 66 mya (Blonder, Royer, Johnson, Miller, & Enquist, 2014) and the end-Triassic extinction c. 201 mya (Soh et al, 2017). However, doubt remains whether plants show clear evidence of mass extinction, even across the largest, the end-Permian mass extinction c. 252 mya.…”

Isotopic and morphologic proxies for reconstructing light environment and leaf function of fossil leaves: a modern calibration in the Daintree Rainforest, Australia

“…Leaf mass per area (LMA), a measure of dry leaf mass per unit of light‐intercepting leaf area, is highly responsive to light conditions (Watson, 1942; Turney et al, 2002; Poorter et al, 2009), and a key determinant and driver of the leaf economic spectrum (Wright et al, 2004; Poorter et al, 2009). Although not directly recorded by fossilized leaves, LMA has been inferred from correlations with petiole dimensions (Royer et al, 2007, 2010), cuticle thickness (Soh et al, 2017), and adaxial epidermal cell density (Haworth and Raschi, 2014). Leaf mass per area is a product of cell size, packing, and leaf thickness, and the acclimation in LMA is driven by a requirement to optimize photosynthetic function on a leaf‐by‐leaf basis (Markesteijn et al, 2007; McMurtrie and Dewar, 2011).…”

Impaired photosynthesis and increased leaf construction costs may induce floral stress during episodes of global warming over macroevolutionary timescales

“…The geographically and temporally extensive fossil record of the Ginkgoales has led to analysis of their potential as indicators of palaeo-environmental and palaeo-climatic conditions. The cuticular micro-morphology of fossil Ginkgoales has been used to reconstruct palaeo-[CO 2 ] 7 , 17 – 19 , indicate the presence of toxic atmospheric gases 20 , characterise the light environment during leaf development (sun versus shade leaves) 19 , 21 , estimate photochemical and non-photochemical usage of light energy 22 and reconstruct leaf economics 23 , 24 . Analysis of the shape of fossil Ginkgoales has also been used to infer exposure to toxic volcanic gases 9 .…”