LANKESTERIANA 7(1-2): 44-46. 2007. UNDERSTANDING THE DISTRIBUTION OF THREE SPECIES OF EPIPHYTIC ORCHIDS IN TEMPERATE AUSTRALIAN RAINFOREST BY INVESTIGATION OF THEIR HOST AND FUNGAL ASSOCIATES 1,3,4 2 3 KELLI M. GOWLAND , ULRIKE MATHESIUS , MARK A. CLEMENTS 1 & ADRIENNE B. NICOTRA 1 School of Botany and Zoology, Australian National University, Bldg 116 Daley Road, Canberra, A.C.T. 0200, Australia 2 School of Biochemistry and Molecular Biology, Australian National University, Bldg 41 Linnaeus Way, Canberra, A.C.T. 0200, Australia 3 Centre for Plant Biodiversity Research, Australian National Herbarium, CSIRO Division of Plant Industry, GPO Box 1600, Canberra, A.C.T. 2601, Australia 4 Author for correspondence: [email protected] KEY WORDS: epiphyte, Aeridinae, orchid mycorrhizal fungi, Ceratobasidium, chemotropism Introduction phytes found on trees and shrubs in temperate rainfor- est gullies. The null hypothesis that we are testing is Understanding the environmental constraints that that these three orchid species are randomly distrib- affect species distributions are critical to the mainte- uted throughout their forest habitat. nance of biodiversity. The abundance of epiphytic More specifically we are addressing the following organisms, those that grow on another substrate, such questions: as a tree or rock, is a direct consequence of the avail- • Do these three epiphytic orchid species exhibit a ability and distribution of these substrates (Ackerman random distribution across the woody plants of the et al. 1989). In the case of epiphytic orchids it is also forest? due to the presence of orchid mycorrhizal fungi • Do these three orchid species associate with all (OMF). For an orchid, crucial to its germination and OMF within their local environment? establishment, is its association with an OMF. The • Do the OMF of these orchid species differ in their OMF provides a carbon source to the developing ability to stimulate germination amongst these orchid embryo (Rasmussen 1995). Although recipro- species? cal carbon transfer has been demonstrated in mature • Are these OMF actively attracted towards the seed plants of a green, terrestrial, orchid species, Goodyera of these three orchid species? repens (Cameron et al. 2006), it is generally believed that OMF receive no immediate benefit from their Methods association with orchids. Therefore, it would appear intuitive that orchids would associate with all OMF To address these questions we surveyed four sites available within their local environment and that they where these three orchid species co-occur in temper- would actively seek this association. ate south-eastern Australia. The woody plant compo- In this investigation we sought to ascertain the sition of the forests and the associations of these three nature of the relationship between three closely relat- orchid species with their phorophytes were deter- ed, co-occurring species of epiphytic, Aeridinae (= mined using a maximum likelihood model. Sarcanthinae) orchids, their OMF, and their phoro- Generalised Linear Mixed Models (GLMMs) were phytes (host trees). The orchid study species: used to detect preferences for physical features of the Sarcochilus hillii, Sarcochilus parviflorus and phorophyte and local environment of these orchid Plectorrhiza tridentata are all small, monopodial epi- species. GOWLAND et al. - Distribution of epiphytic orchids 45 To ensure adequate sampling of the OMF of each imity to moss and location on their phorophytes. orchid species, ten members of each species were sur- Characteristics of the phorophyte that had the greatest veyed from two sites. To investigate the diversity of effect on the size and reproductive potential of the OMF on the preferred phorophyte, five orchids that orchids, as measured by the size and number of were sampled of each species were on the most com- leaves and number of inflorescences, were indepen- mon host. Earlier research indicated that other mem- dent of the species of the phorophyte. bers of these orchid genera associated with the We expected that these distributional differences Ceratobasidiaceae within the form-genus Rhizoctonia would reflect distinct OMF associations with each (Warcup 1981). We also targeted Rhizoctonia-like orchid species; however, whilst different OMF were fungi when we isolated OMF from the roots of these found in association with these orchids it has not orchids. Verification that the isolated fungi were explained the difference in phorophyte species asso- capable of stimulating orchid germination (and there- ciation. All OMF isolated from these three orchid fore, were indeed OMF) was determined by germina- species belonged to two distinct clades, groups, tion trials. Genetic identification of the fungal associ- within the genus Ceratobasidium, recognised as ates was conducted by sequencing the nuclear riboso- clade L and clade K. All three orchid species associ- mal internal transcribed spacer (Gardes & Bruns ated with clade K, but only S. hillii was found with 1993) and the mitochondrial large subunit (White et clade L. This did not, however, explain the random al. 1990), and through the amplification of dispersed distribution of S. hillii, as members of both fungal repetitive DNA sequences (Versalovic et al. 1991). clades were isolated from orchids on the common Finally, to determine if the fungi were actively phorophyte, B. myrtifolia. Additionally, germination attracted towards orchid seed, chemotropism trials trials revealed that even though both groups of fungi were conducted and the amount of fungal growth were not naturally found in association with S. parv- towards test and control aliquots (of seed and water iflorus and P. tridentata, members of each OMF respectively) was compared using Paired t-tests. clade could stimulate germination in all three orchid species ex situ. Results and discussion Furthermore, the chemotropism experiment revealed that members of both OMF clades were Backhousia myrtifolia was the most common tree attracted towards viable orchid seed. This is the first at most sites and was the dominant phorophyte experiment, that we know of, that has demonstrated species for all three orchid species, significantly so that orchid mycorrhizal fungi is actively attracted to for S. parviflorus and P. tridentata. All three orchid orchid seed. species preferred a phorophyte with moderate to high moss cover. Despite these similarities, distinct differ- Conclusion ences in the distribution patterns were detected for each species of orchid. Each orchid species clearly demonstrated charac- These three orchid species differed in the composi- teristic preferences for phorophyte species or features, tion of their phorophyte flora: S. hillii’s distribution indicative of specific ecological niches. They did not approximated a random distribution which reflected exhibit a random distribution throughout the forest. that of the rainforests’ tree species composition; P. Furthermore, despite exposure to multiple potential tridentata exhibited a strong bias towards B. myrtifo- OMF, S. parviflorus and P. tridentata were only lia, although was otherwise on the broadest range of found in association with a restricted subset of those phorophyte species; and S. parviflorus had the nar- available in their local environment. This is despite ex rowest range of phorophytes, exhibiting clear prefer- situ results indicating that there is no inherent physio- ences for and against particular woody plant species. logical reason why they do not associate with both However, the ‘species’ of phorophyte was not the groups of OMF, and the fact that both clades of fungi only correlate with orchid presence, each orchid are actively attracted to orchid seed. species exhibited non-random patterns in their prox- These results typify the intrigue around this family LANKESTERIANA 7(1-2), marzo 2007. © Universidad de Costa Rica, 2007. RD 46 3 IOCC PROCEEDINGS of plants. For example, why would S. parviflorus and Cameron, D.D., J.R. Leake & D.J. Read. 2006. P. tridentata attract, but not utilise all OMF within Mutualistic mycorrhiza in orchids: evidence from their ecosystem? Possible explanations and ideas for plant-fungus carbon and nitrogen transfers in the green-leaved terrestrial orchid Goodyera repens. New further study will be discussed. Phytol. 171: 405-416. Gardes, M. & T.D. Bruns. 1993. ITS primers with ACKNOWLEDGMENTS. We gratefully acknowledge the enhanced specificity for basidiomycetes - application to financial support of the American Orchid Society, the the identification of mycorrhizae and rusts. Mol. Ecol. Australian National University and the CSIRO in funding 2: 113-118. this research, and the Australian Orchid Foundation and Rasmussen, H.N. 1995. Terrestrial Orchids from seed to the Australian Biological Resources Study in their assis- mycotrophic plant. Melbourne, Australia, Cambridge tance with attending this conference. We would also like to University Press. thank: J. Wood for his assistance with the analysis of the Versalovic, J., T. Koeuth & J.R. Lupski. 1991. Distribution ecological data; M. van der Merwe, C. Linde, B. Pfeil, T. of repetitive DNA sequences in eubacteria and applica- Otero and R. Bayer for their advice in deciphering the tion to fingerprinting of bacterial genomes. Nucl. Acids identity of these OMF; and to S. Refshauge and the Res. 19: 6823-6831. CSIRO microscopy unit for technical advice on the Warcup, J.H. 1981. The mycorrhizal relationships of microscopy and chemotropism experiments. Australian orchids. New Phytol.