Species-specific chemical allometry of Alethopteris ambigua and Neuropteris ovata var. simonii (Late Pennsylvanian, Canada).

D`ANGELO J A

Congreso; Reunión de comunicaciones de la Asociación Paleontológica Argentina; 2023

In living plants, allometry studies how different characteristics of various plant parts scale with plant overall size. This is useful for understanding the growth patterns of plants and how they allocate resources to different tissues and organs during growth. Allometric equations (models) predict plant traits based on simple measurements, providing information ranging from individual plant productivity to ecosystems carbon stocks. Allometric studies of fossil plants are scarce and determining allometric models to estimate plant size and growth patterns presents a unique challenge. This study aims at developing species-specific allometric models for estimating the proportions and relationships between the diameter of different-order rachises and their chemical composition. Ultimate, penultimate, and antepenultimate rachises (Urs, PUrs, APUrs, respectively) of two compression-preserved fronds are analyzed by Fourier transform infrared (FTIR) spectroscopy. Studied specimens include the largest-known frond segments of Alethopteris ambigua (45 cm long) and Neuropteris ovata var. simonii (65 cm long), originating from the late Pennsylvanian Sydney Coalfield in Nova Scotia, Canada. Specimens are on deposit with the palaeobotanical fossil collection of Cape Breton University (accession numbers: 84-520 - A. ambigua - and 985 GF-248 - N. ovata var. simonii). Results indicate that, within each frond, FTIR functional-group ratios (IR ratios) vary in relation to rachis diameters along the proximal-to-distal frond sections. This demonstrates allometric relationships and, using power equations, allometric models are developed for each species by evaluating the statistical relationships of diameter (D) of Urs, PUrs, APUrs at different frond positions and a number of IR ratios in the form: Log10 (IR ratio) = a + b (Log10 D). Main conclusions highlight the different ecological strategies of the studied taxa: N. ovata var. simonii had relatively lower allocation rates of specific aromatics, suggesting a slow-growing species with greater resource conservation, i.e., a “slow-return” or conservative species. Conversely, A. ambigua had a relatively higher allocation rates of different aromatics, suggesting a fast-growing species with rapid resource acquisition, i.e., a “fast-return” or acquisitive species. The chemistry variation of Urs, PUrs, APUrs shown by the specimens at a particular ontogenetic or developmental stage at the time of fossilization proves useful for allometric studies. Allometric models provide a better understanding of the scaling of plant ecological variables, such as metabolic rates, population dynamics, and resource consumption, across different fossil taxa. These models aid in the reconstruction of extinct ecosystems, shedding light on their evolution over time.