Mixed Arbuscular Mycorrhizae from the Triassic of Antarctica

Abstract

Arbuscular mycorrhizae are the most ubiquitous of mycorrhizal fungi, that have formed mutualistic relationships with virtually almost all major groups of vascular plants. Five genera of arbuscular endomycorrhizal fungi are currently delineated, but fossil arbuscular mycorrhizae have been allied with only two, Glomus and Sclerocystis. A Triassic arbuscular mycorrhiza described inhabiting the roots of Antarcticycas was originally allied with Glomus. It is now known to be a mixed colony comprised of fungi attributable to the suborders Glomineae and Gigasporineae of the Glomales, described as two new species. The fossil Gigasporinean mycorrhiza is characterized by irregularly swollen intercellular and intracellular hyphae that are coiled extensively within the cells. Arbuscules have thick trunks and narrow branches. In the Glominean form, hyphal diameter is more uniform,with coiling rarely present. Arbuscules have thin trunks and fine branches. Vesicles may be lateral or terminal. Spores are not present; therefore, the probability of more than one species of each suborder being represented cannot be conclusively demonstrated. This provides the first fossil representative of the Gigasporineae and supports current rDNA estimates of the age of the lineage. Moreover, it is the first reported instance of a mixed colony of arbuscular endomycorrhizae in the fossil record.

Response of Mycorrhizal Diversity to Current Climatic Changes

“… Immediate (1-2 years) impacts associated with ecosystem fragmentation and habitat loss will be immediately realized through the removal of plant-hosts and significant disturbance of the soil/rhizosphere habitat of mycorrhizas (Figure 5c)  Short-term (3-10 year) impacts: where biotic invasions from exotic mycorrhizal fungi, plant and pests, diseases and other abiotic perturbations (such as the impacts of natural volcanism) will be realized (Figure 5c)  Intermediate-term (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) year) impacts: where the cumulative and additive effects of increased N deposition, soil acidification and pollutants will be realized (Figure 5c)  Long-term (21-50+ year) impacts: where increased temperatures associated with CO 2 increase will result in the destabilization of global rainfall patterns, combining to have significant impacts on plant ecosystem resilience (Figure 5c). The above-and below-ground impacts of chronic/catastrophic ecosystem modification that results in permanent land-use change will potentially result in:…”

“…Pollutants (Intermediate-term Impacts Occurring in [11][12][13][14][15][16][17][18][19][20] Alteration to the nutritional balance of soils through the enrichment of N, decrease in soil pH (e.g., through enrichment with NOx and SOx) and addition of environmental pollutants will potentially result in:…”

Fossil fungi with suggested affinities to the Endogonaceae from the Middle Triassic of Antarctica

“…However, only a few of these remains have provided information on the precise systematic affinities, nutritional modes and ecology of the fungi (e.g. Stubblefield et al 1987;Phipps and Taylor 1996;Schwendemann et al 2009Schwendemann et al , 2010Schwendemann et al , 2011. Among the fungal fossils from the Fremouw Formation are several forms interpreted as zygomycetous spores and sporocarps containing spores (Taylor and White 1989;Taylor 1989, 1991).…”

“…Taylor et al 1994Taylor et al , 2005Krings et al 2007Krings et al , 2009Krings et al , 2010Dotzler et al 2011), as well as in Triassic (251 000 000-199 000 000 y ago) permineralized peat from Antarctica (e.g. Stubblefield et al 1987, White and Taylor 1988, Osborn and Taylor 1989, Taylor and White 1989, Phipps and Taylor 1996, Schwendemann et al 2011.…”

Mycorrhizal Fungi: Their Habitats and Nutritional Strategies

“…Such an ancient origin anticipates emergence of vascular terrestrial plants, and the thallus of bryophyte-like precursors had associations resembling modern arbuscular mycorrhizas even before roots evolved (reviewed in Brundrett 2002). Thus, the hypothesis has been put forward that symbiosis was a key factor in the colonization of land by plants (Taylor et al 1995;Phipps and Taylor 1996). Modern arbuscular mycorrhizal (AM) fungi comprise a number of ancient lineages (Redecker et al 2000b;Schüßler et al 2001a;Schüßler 2002), which based on morphological, biochemical and ecological traits, can unequivocally be separated from all other major fungal groups.…”