Dick Wettenhall probes the underworld of this miraculous plant (including sexual deception) and reveals the threat posed by sand mining to some of Victoria’s rarest orchid communities. Photo: Kalgoorlie Donkey Orchid (Diuris brumalis) By Dick Wettenhall
A SEMINAL moment for me was the discovery of spectacular Donkey Orchids growing in virtual sand south of Kalgoorlie. With no water in sight, I wondered how these delicate plants survived.
I am reminded of this when driving past the sand mine-scarred bushlands along Western Port’s shoreline stretching from Lang Lang to Glen Forbes. Disturbingly, this is one of Bass Coast’s few remaining areas of remnant bushland, and home for some of Victoria’s rarest orchids.
The survival of these orchids, as with Kalgoorlie’s Donkey Orchids, is the product of millions of years of evolutionary adaptation to the extraordinarily intricate underground ecology of dry nutrient-poor soils. Tragically, it only takes seconds for sand mining bulldozers and excavators to irreversibly destroy these remarkable ecosystems.
A SEMINAL moment for me was the discovery of spectacular Donkey Orchids growing in virtual sand south of Kalgoorlie. With no water in sight, I wondered how these delicate plants survived.
I am reminded of this when driving past the sand mine-scarred bushlands along Western Port’s shoreline stretching from Lang Lang to Glen Forbes. Disturbingly, this is one of Bass Coast’s few remaining areas of remnant bushland, and home for some of Victoria’s rarest orchids.
The survival of these orchids, as with Kalgoorlie’s Donkey Orchids, is the product of millions of years of evolutionary adaptation to the extraordinarily intricate underground ecology of dry nutrient-poor soils. Tragically, it only takes seconds for sand mining bulldozers and excavators to irreversibly destroy these remarkable ecosystems.
Soil is a living organism whose functions and health form the foundation of terrestrial life. Farmers learned this lesson the hard way in pursuit of higher yields in agriculture dependent on clearing of bushland, heavy ploughing, overcropping and excessive use of agrichemicals. These practices reaped short-term benefits but destroyed the underground ecology essential for soil health. Consequently, fertile land was transformed into vast wastelands unfit for agriculture and prone to rampant erosion.
Casualties of the grab for sand. Western Port in the background. While farmland management practices have improved, the ongoing destruction of natural soils and their resident ecosystems by human interventions continues unabated. Amongst the most damaging interventions are the type of sand mining operations occurring in Western Port’s coastal bushlands.
Sand mining destroys the soil architecture providing frameworks for interconnected networks of underground ecosystems, so vitally important for sustaining the health of above-ground flora and fauna. It’s the equivalent of blowing up entire housing estates and expecting the occupants to survive and continue being productive.
Soil architecture is based on microaggregates of particles incorporating minerals and organic carbon and nitrogen. Communities of bacteria, fungi and other microbes occupy specialised niches within these structures, forming interconnected microbial villages which vary in composition depending on their proximity to water, oxygen and nutrients. They are connected through fungal (mycorrhizal) filaments, porous cavities and moisture tracts, allowing for the transfer of oxygen, nutrients and viruses between the villages.
Underground ecosystems function both as the lungs and stomach of living soils. Oxygen is delivered to the microbial villages where resident bacteria extract essential minerals from soil particles and fix inorganic nitrogen. Together with invertebrate soil dwellers and other microbes, they decompose plant and animal detritus. The nutrients released and soil water are absorbed by mycorrhizal filaments and transported back to the roots of plants, thereby sustaining above-ground flora and fauna.
Evolutionary adaptations have enabled orchids to exploit these environments in two general ways: first, specialised underground germinating seed and root adaptations enable the symbiotic couplings with mycorrhizal filaments, necessary for water and nutrient transport and delivery; secondly, adaptations of flower morphologies give individual species a competitive advantage in pollination and, hence, reproduction.
Critical structural adaptions enabling orchids to better compete for water and nutrients are receptors for fungal filaments. These are formed on the walls of germinating seeds, embryos (protocorms) and root systems, including tubers which store nutrients to sustain dormancy and vegetive growth. The receptors can only couple with a single species of orchid-specific mycorrhiza. The fungal networks function as root extensions accessing sources of nutrients and moisture some distance from their symbiotic hosts.
Sand mining destroys the soil architecture providing frameworks for interconnected networks of underground ecosystems, so vitally important for sustaining the health of above-ground flora and fauna. It’s the equivalent of blowing up entire housing estates and expecting the occupants to survive and continue being productive.
Soil architecture is based on microaggregates of particles incorporating minerals and organic carbon and nitrogen. Communities of bacteria, fungi and other microbes occupy specialised niches within these structures, forming interconnected microbial villages which vary in composition depending on their proximity to water, oxygen and nutrients. They are connected through fungal (mycorrhizal) filaments, porous cavities and moisture tracts, allowing for the transfer of oxygen, nutrients and viruses between the villages.
Underground ecosystems function both as the lungs and stomach of living soils. Oxygen is delivered to the microbial villages where resident bacteria extract essential minerals from soil particles and fix inorganic nitrogen. Together with invertebrate soil dwellers and other microbes, they decompose plant and animal detritus. The nutrients released and soil water are absorbed by mycorrhizal filaments and transported back to the roots of plants, thereby sustaining above-ground flora and fauna.
Evolutionary adaptations have enabled orchids to exploit these environments in two general ways: first, specialised underground germinating seed and root adaptations enable the symbiotic couplings with mycorrhizal filaments, necessary for water and nutrient transport and delivery; secondly, adaptations of flower morphologies give individual species a competitive advantage in pollination and, hence, reproduction.
Critical structural adaptions enabling orchids to better compete for water and nutrients are receptors for fungal filaments. These are formed on the walls of germinating seeds, embryos (protocorms) and root systems, including tubers which store nutrients to sustain dormancy and vegetive growth. The receptors can only couple with a single species of orchid-specific mycorrhiza. The fungal networks function as root extensions accessing sources of nutrients and moisture some distance from their symbiotic hosts.
The Rosy Hyacinth Orchid ((Dipodium roseum) is pollinated by bees. Orchid photos by Dick Wettenhall were all takenin The Gurdies and Grantville conservation reserves.
All orchids are fully dependent on mycorrhiza at the seed germination and protocorm stages. Seedlings and adult orchids with photosynthetic capability also benefit from but are not totally dependent on the fungi for nutrients. However, orchids without green leaves for photosynthesis, such as Potato and Hyacinth orchids, are fully dependent on mycorrhiza for nutrients throughout life.
These evolutionary adaptations are facilitated by patchy distributions of the orchid-specific mycorrhiza, resulting in local spatial segregation of orchid species important for developing biodiversity.
These types of symbiotic adaptations are not restricted to orchids. For example, the remnant bushland impacted by sand mining is home for ancient Xanthorrhoea grass trees which, in over 400 million years of evolution, have adapted to the nutrient-poor sandy soils of these bushlands.
The general functions of fungal networks and their symbiotic interactions with grass trees are similar, although different species of mycorrhiza are involved. The grass trees are critically dependent on their mycorrhizal partners for water, phosphorus, sulphur and other mineral nutrients. However, unlike orchids, grass trees produce all the sugar they require and can reward the fungus with excess sugars and other organic compounds.
The evolutionary adaptations of orchid flowers are more easily recognised and appreciated because of their amazingly elegant and beautiful structures and colours. These adaptations provided core evidence supporting Charles Darwin’s theory on the origin of species. His book The Various Contrivances by Which Orchids are Fertilised by Insects is an extraordinary record of the intergenerational ‘gradations’ in orchid flower anatomy.
Particularly important were reproductive structures which specifically prevent self-pollination (in fact, we now know that some orchids such as Tiny Finger Orchids only self-pollinate) and attract male insect pollinators through sexually deceptive species mimicry of both floral characters and insect morphologies.
These evolutionary adaptations are facilitated by patchy distributions of the orchid-specific mycorrhiza, resulting in local spatial segregation of orchid species important for developing biodiversity.
These types of symbiotic adaptations are not restricted to orchids. For example, the remnant bushland impacted by sand mining is home for ancient Xanthorrhoea grass trees which, in over 400 million years of evolution, have adapted to the nutrient-poor sandy soils of these bushlands.
The general functions of fungal networks and their symbiotic interactions with grass trees are similar, although different species of mycorrhiza are involved. The grass trees are critically dependent on their mycorrhizal partners for water, phosphorus, sulphur and other mineral nutrients. However, unlike orchids, grass trees produce all the sugar they require and can reward the fungus with excess sugars and other organic compounds.
The evolutionary adaptations of orchid flowers are more easily recognised and appreciated because of their amazingly elegant and beautiful structures and colours. These adaptations provided core evidence supporting Charles Darwin’s theory on the origin of species. His book The Various Contrivances by Which Orchids are Fertilised by Insects is an extraordinary record of the intergenerational ‘gradations’ in orchid flower anatomy.
Particularly important were reproductive structures which specifically prevent self-pollination (in fact, we now know that some orchids such as Tiny Finger Orchids only self-pollinate) and attract male insect pollinators through sexually deceptive species mimicry of both floral characters and insect morphologies.
Darwin’s conclusions were later extended by Australia’s remarkable Edith Coleman, who discovered the chemical basis for insect-specific orchid pollination: Male insects are lured to orchids by chemical mating signals (scents/pheromones secreted by females), where they are ‘rewarded’ by being induced to pseudocopulate on orchid labellum resembling female reproductive organs, and then forced to pick up pollen before escaping. To gain a competitive advantage, individual orchid species use the specific scent emitted by the female counterpart of the male pollinator species, which include wasps, saw flies, bees, fungal gnats and midges.
Different orchid species exhibit an extraordinary array of flower morphologies: for example, compare Greenhood, Flying Duck, Donkey, Purple Beard, Little Fingers and Hyacinth Orchids.
In addition to sexual deception-based morphology, orchids also lure insects by mimicking whole flower shapes and colours or nectar glands of other plants. For example, insect pollinators attracted to donkey orchids, sun orchids or leek orchids feed off the similar-looking flowers of native pea legumes, iris (Patersonia), lilies (Dianella) and grass trees (Xanthorrhea). Remarkably, the orchid flowering is coordinated with the breeding of both the insect pollinators and the development of other plants providing nectar.
The dynamic interconnected communities of remnant bushland biota are not only wonders to observe but also invaluable scientific resources. Of particular significance are the soil ecosystems which serve as museums of evolutionary adaptations. Elucidation of these adaptations will underpin future innovations in soil health preservation, environmental protection and sustainable agriculture. Such innovations will be of vital importance for the capacity of future generations to deal with population growth and climate change.
Shockingly, the soil ecosystems that sustain these wonders of nature are being progressively destroyed by the ever-expanding sand mining operations in our region. There are at least six mines already established in the corridor of remnant bushlands extending from The Gurdies to Glen Forbes. Several more are in the planning stage.
Unless contained, such relentless expansion of the industry will lead to the irreversible loss of much of the remaining remnant bushlands and, hence, restrict biodiversity. This heart-breaking prospect will cause much grief unless governments can be convinced to give higher priority to environmental impact issues, when considering permit applications for industrial activities that will destroy the soils that sustain our precious bushlands.
Dick Wettenhall is a former professor of biochemistry and molecular biology at Melbourne University. He also owned and operated The Gurdies Winery until this year. The biology of vineyard soils was a particular interest.
Different orchid species exhibit an extraordinary array of flower morphologies: for example, compare Greenhood, Flying Duck, Donkey, Purple Beard, Little Fingers and Hyacinth Orchids.
In addition to sexual deception-based morphology, orchids also lure insects by mimicking whole flower shapes and colours or nectar glands of other plants. For example, insect pollinators attracted to donkey orchids, sun orchids or leek orchids feed off the similar-looking flowers of native pea legumes, iris (Patersonia), lilies (Dianella) and grass trees (Xanthorrhea). Remarkably, the orchid flowering is coordinated with the breeding of both the insect pollinators and the development of other plants providing nectar.
The dynamic interconnected communities of remnant bushland biota are not only wonders to observe but also invaluable scientific resources. Of particular significance are the soil ecosystems which serve as museums of evolutionary adaptations. Elucidation of these adaptations will underpin future innovations in soil health preservation, environmental protection and sustainable agriculture. Such innovations will be of vital importance for the capacity of future generations to deal with population growth and climate change.
Shockingly, the soil ecosystems that sustain these wonders of nature are being progressively destroyed by the ever-expanding sand mining operations in our region. There are at least six mines already established in the corridor of remnant bushlands extending from The Gurdies to Glen Forbes. Several more are in the planning stage.
Unless contained, such relentless expansion of the industry will lead to the irreversible loss of much of the remaining remnant bushlands and, hence, restrict biodiversity. This heart-breaking prospect will cause much grief unless governments can be convinced to give higher priority to environmental impact issues, when considering permit applications for industrial activities that will destroy the soils that sustain our precious bushlands.
Dick Wettenhall is a former professor of biochemistry and molecular biology at Melbourne University. He also owned and operated The Gurdies Winery until this year. The biology of vineyard soils was a particular interest.
The Adams Creek Nature Conservation Reserve, Lang Lang, with sand mine in foreground.
Photo: Woodrow Wilson
Photo: Woodrow Wilson