Abstract Detail

Paleobotany

Imada, Yume [1], Stockey, Ruth A. [2], Rothwell, Gar W. [3], Tomescu, Alexandru M. F. [4].

Plant-fungal associations in endomycorrhizal root nodules of Early Cretaceous conifers (Vancouver Island, Canada).

A number of conifers typically develop specialized root nodules that host vesicular-arbuscular endomycorrhizal fungi. Benefitting from these root symbioses, nodule-bearing conifers often thrive in nutrient-poor habitats. The evolutionary and functional significance of conifer root nodules have therefore attracted much attention. Although conifer mycorrhizal root nodules are known as early as the Middle Triassic, the fossil record of this type of association is notably sparse. We describe mycorrhizal root nodules from the Early Cretaceous (Valanginian, ca. 136 Ma) permineralized plant assemblages at Apple Bay (Vancouver Island, Canada). The nodules range in shape from spherical to conical. They occur dispersed in the rock matrix or attached to root fragments in dense clusters; some show regenerative growth (nodule-on-nodule). Anatomically, they include a vascular cylinder surrounded by an endodermis, a thick cortex with large parenchyma, markedly constricted at the nodule base, and a well-defined epidermis; phi-thickenings are sometimes present in the inner cortical parenchyma. The cortex of the nodules is the principal site of fungal infection where hyphae of different sizes, hyphal coils, arbuscule-like structures, and vesicles (spores?) are present within the cells. Fungal structures are more rarely preserved in the epidermis and may be absent in the stele of the nodules; we are currently investigating potential tissue specificity of the different types of structures. The xylem anatomy of the roots and the bordered pits of tracheids in both nodules and subtending roots are consistent with conifer affinities; the anatomy of the nodules is closely similar to that of extant conifer nodules. Among extant conifers, mycorrhizal nodules are known in Araucariaceae, Sciadopitys, and Podocarpaceae. Of these, phi-thickenings are known in the former two and are rare (or absent) in the Podocarpaceae. Additionally, the presence of Podocarpaceae in the Cretaceous of North America has yet to be ascertained. Together, these point to Sciadopitys or Araucariaceae as the probable producers of the nodules. Sciadopitys-like foliage has been observed in the Apple Bay assemblage, wherein the dominant conifers are Pinaceae and Cupressaceae. While the presence of Araucariaceae in this assemblage is uncertain, the family was present in western North America since at least the Jurassic. Irrespective of the exact affinities of the Apple Bay nodules, they mark the first occurrence of anatomical preservation of such structures in the Cretaceous - providing cellular details that represent a rich source of information on plant-fungal associations during this interval -, and only the eighth documented occurrence in the Mesozoic worldwide.

Related Links:
Yume Imada

1 - Ehime University, Graduate School of Science And Engineering, Matsuyama, Ehime, 7908577, Japan
2 - Oregon State University, Department of Botany and Plant Pathology, Corvallis, OR, 97331, USA
3 - Ohio University, Department of Environmental and Plant Biology, Athens, OH, 45701, USA
4 - Humboldt State University, Department of Biological Sciences, Arcata, CA, 95521, USA

Keywords:
arbuscular mycorrhizal fungi
plant-fungal interactions
anatomy
mesozoic
Cretaceous
root nodule
Paleobotany
Fossil
conifer.

Presentation Type: Oral Paper
Session: PL6, Paleobotany: Paleozoic/Mesozoic Paleobotany
Location: /
Date: Thursday, July 22nd, 2021
Time: 11:00 AM(EDT)
Number: PL6005
Abstract ID:68
Candidate for Awards:None