Chemical, biomechanical, and physiological characteristics of Xylopteris argentina (Corystospermaceae, Triassic, Mendoza, Argentina)

D`ANGELO J A

Workshop; 1° Reunión Virtual de Comunicaciones de la Asociación Paleontológica Argentina; 2020

This contribution focuses on the relationships amongst chemical composition and biomechanical/physiological characteristics of compression-preserved specimens of Xylopteris argentina (Kurtz) Frenguelli emend. Stipanicic et Bonetti (1995). Studied specimens (CPb-N46a(3), CPb-N46a(4), CPb-N46b(2), and CPb-P373) originated from Cacheuta (Norian; Mendoza, Argentina). Studied properties of leaves include: density, tensile strength (resistant to fracture), tensile modulus of elasticity (stiffness), flexural stiffness (total resistance to bending), leaf mass per area (metabolic cost of tissue construction), and photosynthetic capacity. They were calculated using a spectroscopic (infrared)-based, 3D-multivariate model and trait relationships linking density and the properties mentioned above, which have been established for leaf tissues of living plants. X. argentina leaves have a predominantly aromatic chemical composition. Mean values of biomechanical/physiological properties include: density = 0.86 g/cm3, stiffness = 3.15 MPa, resistance to bending = 1x10-5 Nm2, metabolic construction costs = 0.62 g/cm2, and photosynthetic capacity = 68 nmol g-1 s-1. Results suggest that, theoretically, the once-living plants bearing X. argentina invested considerable amounts of resources for the construction of aromatic, high-density, and metabolically expensive foliar tissues. Tough, rigid, and brittle pinnae had a photosynthetic activity more similar to that of some sclerified/lignified axial structures [e.g., midveins of Dicroidium obtusifolium (Johnston) Townrow and rachises (with considerable larger diameters) of Dicroidium odontopteroides (Morris) Gothan] than to pinnule laminae. It is concluded that X. argentina pinnae were similar to ?flat rachises? employing combined strategies that optimized the biomechanical stability and physiological activities of a stress-tolerant plant inhabiting oligotrophic habitats, typical of some low-productivity, Gondwanan Triassic ecosystems.