27 Nov 2017

Conservation of a Critically Endangered Orchid Drakaea Elastica Lindl. in the Context of Nutritional Requirements and Saprophytic Competency of the Mycorrhizal Fungus and its Propagation

Siti Nurfadilah, 2010
The University of Western Australia

Abstract

Drakaea elastica is a critically endangered orchid species that is a habitat specialist of nutrient deficient sandy soil and is dependent on a slow growing mycorrhizal fungus for its nutrient supply in its entire life cycle. In the conservation of this species, understanding the biology and ecology of the mycorrhizal fungus, especially the critical aspects determining the growth and the survival of themycorrhizal fungus, is essential. The aim of this research is to investigate nutritional requirements, factors limiting the growth and survival, and saprophytic competency of the slow growing mycorrhizal fungus of Drakaea elastica in terms of its capacity to utilize a variety of nutrient sources (C, N, and P) relative to other sympatric faster growing orchid mycorrhizal fungi. The assessment of the capacity of Drakaea elastica mycorrhizal fungus in axenic liquid media containing single nutrient sources showed that it utilised a variety of C, N, and P sources for its growth. A wide range of C sources that Drakaea elastica mycorrhizal fungus required for its growth encompassed glucose and mannose (monosaccharide), cellobiose (disaccharide), cellulose, pectin, starch, and xylan (polysaccharides). The mycorrhizal fungus did not grow on the other C substrates, galactose, rhamnose, arabinose (monosaccharide) and tannic acid (polysaccharides). Ammonium, a variety of amino acids (aspartic acid, glutamic acid, glutamine, asparagine, alanine, arginine, and glycine), and protein BSA are essential N sources required for the growth of Drakaea elastica mycorrhizal fungus. Drakaea elastica did not utilize nitrate, histidine, and proline as the N source for its growth. In terms of the requirement of P which is critically needed, Drakaea elastica mycorrhizal fungus utilised all forms of P sources including inorganic P (orthophosphate) and organic P (phytic acid and DNA). This investigation of nutritional requirements of Drakaea elastica is important to understand which nutrient sources required by Drakaea elastica mycorrhizal fungus for its robust growth. These data can also be a basis for an understanding of how Drakaea elastica mycorrhizal fungus utilizes different nutrient sources.

Drakaea elastica mycorrhizal fungus utilised the same C, N, and P sources with the sympatric faster growing orchid mycorrhizal fungi suggesting that it has to compete for the same nutrient sources. With its slow growing characteristic, Drakaea elastica mycorrhizal fungus presumably has lower competency to access nutrient sources relative to faster growing fungi. This may explain the specialisation of Drakaea elastica mycorrhizal fungus in nutrient deficient sandy soil to avoid competition with many other fungi.

The growth and survival of Drakaea elastica mycorrhizal fungus was limited by the availability of an external source of the organic compounds thiamine and PABA. The ability of Drakaea elastica mycorrhizal fungus to utilize a wide range of C, N, and P sources was determined by the availability of these organic compounds which are important in the major metabolism for growth. Without these organic compounds, Drakaea elastica mycorrhizal fungus grew poorly on most C, N, and P sources. The findings of this study can be incorporated into the biology and ecology of Drakaea elastica mycorrhizal fungus which is important in the conservation of Drakaea elastica. In the propagation of Drakaea elastica, understanding the biology and ecology for the seedlings development and establishment is important to optimise propagation of this critically endangered orchid species.

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