Biological decay by microorganisms in stems from the Upper Triassic Ischigualasto Formation (San Juan Province, Argentina): a striking microbial diversity in Carnian-Norian terrestrial ecosystems

SAGASTI, A.J.; BODNAR, JOSEFINA

REVIEW OF PALAEOBOTANY AND PALYNOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2023

0034-6667

We studied degradation patterns and microorganisms preserved in permineralized stemsof Rhexoxylon piatnitzky, Protojuniperoxylon ischigualastense, and Agathoxylonargentinum from the Valle de la Luna Member of the Ischigualasto Formation (UpperTriassic, San Juan, Argentina). All three species show loss of middle lamella, thinning,and whitening of tracheid cell walls, and detachment of the S3 layer, consistent withselective delignification by white rot. This type of rot is the product of lignin andcellulosic degradation by Basidiomycetes and Ascomycetes. Rhexoxylon piatnitzkyi alsoshows small cavities, more or less circular in outline, on the wall of tracheids. This isknown as soft rot and can be produced by some Ascomycetes, the anamorphic phases ofdiverse fungi, and tunneling bacteria. Additionally, abundant and diversemicroorganisms were found. Rhexoxylon piatnitzkyi shows fragments of septate hyphae,evidence of bacterial activity, and structures of unknown affinity. Protojuniperoxylonischigualastense presents structures common to anamorphic phases of diverse fungi,such as chlamydospores and conidiophores. Lastly, Agathoxylon argentinum bearscoiled and septate hyphae, and a fan-shaped mycelium, whose significance is discussed.The microbiological study was complemented by the assessment of sedimentary andtaphonomic data of the fossil-bearing beds. A gradual increment in humidity for theValle de la Luna Member is interpreted, which concludes with a humidity peak in itsupper section. This contribution represents the first detailed study of xylophagous andsaprophyte micro-communities for the Ischigualasto Formation. The abundance anddiversity of microorganisms described illustrate the complexity of wood-inhabitingmicro-communities from the Carnian-Norian interval of Argentina.