Inorganic and organic substrates as sources of nitrogen and phosphorus for multiple genotypes of two ericoid mycorrhizal fungal taxa from Woollsia pungens and Leucopogon parviflorus (Ericaceae)

The abilities of six genotypes of two putative Helotiales ascomycete ericoid mycorrhizal fungal taxa from Woollsia pungens Cav. (Muell.) and Leucopogon parviflorus (Andr.) Lindl. (Ericaceae) to utilise a range of nitrogen and phosphorus compounds for growth were tested in axenic liquid culture. Although significant intra- and interspecific variation was observed, genotypes of both taxa utilised NH4+, NO3–, a range of acidic, neutral and basic amino acids and bovine serum albumen as sole nitrogen sources, along with orthophosphate, inositol hexaphosphate and DNA as sole phosphorus sources. For several isolates of each taxon, growth on the sulfur-containing amino acid cysteine was increased significantly when other forms of sulfur were excluded from the growth medium, suggesting that cysteine utilisation may represent a sulfur-scavenging strategy. Pooled data for all genotypes indicated that Taxon II produced significantly greater biomass on most substrates; however, in no case did this differ by an order of magnitude or more. Both taxa thus appear likely to have broadly similar abilities to obtain nitrogen and phosphorus from organic substrates on soil.

Spatial distribution of fungal endophyte genotypes in a Woollsia pungens (Ericaceae) root system

Fungal endophytes were isolated from hair roots of Woollsia pungens Cav. (Muell.) and mapped according to the root portions from which they were isolated. A total of 119 isolates was obtained and restriction fragment length polymorphism (RFLP) analysis of the internal transcribed spacer (ITS) region indicated that the isolate assemblage comprised five RFLP types. ITS sequence comparison revealed that RFLP Types I and II had 99.6–99.8% sequence identity with known ericoid mycorrhizal endophytes from Australian epacrids. The remaining three RFLP types were most similar to non-mycorrhizal ascomycetes. Eighty-five per cent of isolates obtained were of RFLP Type I and these were widespread within the root system. Inter-simple sequence repeat PCR suggested that 94% of RFLP Type I isolates were of a single genotype that was widely distributed within the root system, with the remaining five isolates each representing a different genotype. Apparent spatial dominance of the root system by a single fungal genotype may indicate limited functional diversity in the mycorrhizal endophyte assemblage.

Metal insensitivity in ericoid mycorrhizal endophytes from Woollsia pungens (Epacridaceae)

The influence of Cd2+, Cu2+ and Zn2+ on biomass production by 13 ericoid mycorrhizal endophytes (all putative Leotiales ascomycetes) from Woollsia pungens (Epacridaceae), along with three isolates of Hymenoscyphus spp., was investigated in axenic liquid culture. Inter- and intraspecific variation was observed in effective concentration values that inhibited growth by 50% (EC50) for each metal; however, values varied by only a single order of magnitude for a particular metal (16.67–261.00 mmol m–3 for Zn2+, 2.50–12.33 mmol m–3 for Cd2+ and 3.00–43.88 mmol m-3for Cu2+). Values of EC50 for the endophytes from W. pungens were thus broadly similar to those from H. ericae. Combined metal treatments had either additive or ameliorative effects on the toxicity of individual metals to the various isolates. The data suggest that resistance to toxic metals is broadly similar in ericoid mycorrhizal endophytes from Northern Hemisphere Ericaceae and Australian Epacridaceae.