Fungi as Architects of the Rimstone Dams in Huanglong, NSD, Sichuan, China

Abstract

The Huanglong park area of the Sichuan Province of China is a unique scenic area of the world. It is known for its thousands of aquamarine-colored pools that are formed behind naturally formed rimstone dams of travertine (calcite) along a cold water stream. The travertine, based on its crystalline structural analysis, is of biological origin. This makes sense since the temperature of the waters of Huanglong varies from 5 to 7 °C and thus geochemical crystallization does not occur as it does in other locations around the world possessing thermal pools whose structures are primarily formed through cooling processes. Fungi and bacteria were discovered associated with both leaves associated with the calcite dams as well as in the older parts of well-established dams. Several species of Phytium, a phycomycete and an endophyte, accounted for over 45 % of all of the fungi successfully isolated from the well-established dam samples and at least 85 % in the floating leaf samples. Saprolegnia spp. (Phycomycetes) along with Phoma spp. (Ascomycetes) were noted along with Mortierella sp. as other dam-associated fungi. The fungal hyphae observed on dead leaf material as well as in the calcite dams directly served as nucleation points for the formation of crystalline CaCO. Eventually, these crystals grow large enough to fuse to make calcite plates which form the main structural feature of all of the travertine dams in this area. Interestingly, each of the individual crystals associated with the dams has an associated hole in its core where a fungal hypha used to reside as observed by scanning electron microscopy. While diatoms were present in the analysis, they too seem to contribute to the structure of the dams but in a minor way. The only bacteria isolated from the older dam of this aquatic environment were Pseudomonas spp. and their role in dam formation is uncertain. Huanglong is a unique and beautiful place, and the water features present in this area can definitely be attributed to those fungal architects that encourage calcite crystal formation.

A review on the potential of filamentous fungi for microbial self-healing of concrete

“…Biomineralization such as CaCO 3 precipitation and the ability to take up metals by fungi has already been explored for other applications. Xie et al reported the role of fungi in the development of the naturally formed Rimstone Dams in the Huanglong park area of the Sichuan Province of China [64]. Fungal hyphae serve as nucleation points for the formation of crystalline CaCO 3 , which then grows to fuse into calcite plates resulting in the main structural framework of the travertine dams in this area [64].…”

“…Xie et al reported the role of fungi in the development of the naturally formed Rimstone Dams in the Huanglong park area of the Sichuan Province of China [64]. Fungal hyphae serve as nucleation points for the formation of crystalline CaCO 3 , which then grows to fuse into calcite plates resulting in the main structural framework of the travertine dams in this area [64]. Crystalline structural analysis of the travertine proved its biological origin and the crystals each showed a hole in their core where a fungal hyphae used to reside [64].…”

“…Fungal hyphae serve as nucleation points for the formation of crystalline CaCO 3 , which then grows to fuse into calcite plates resulting in the main structural framework of the travertine dams in this area [64]. Crystalline structural analysis of the travertine proved its biological origin and the crystals each showed a hole in their core where a fungal hyphae used to reside [64]. From the retrieved samples, examination showed that the oomycetes Pythium and Saprolegnia were dominantly present, with oomycetes being a group of filamentous fungal-like eukaryotes that are phylogenetically more closely related to algae [65].…”