Some orchids share resources with their seedlings, in what seems to be a form of parental care by plants.
The young seedlings don鈥檛 have chlorophyll, so are unable to make their own food through photosynthesis, and biologists were in the dark about where the tiny plants got their nutrition from.
鈥淪eedlings are often seen in clusters around adult orchids,鈥� says at the University of Sheffield, UK, 鈥渁nd our results support the idea that this could be driven by a 鈥榩arental nurture鈥� mechanism involving transfer of carbon compounds across generations.鈥�
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Like most plants, orchids in the wild form links with fungi. Field and her colleagues have shown that the adult orchids send parental care packages of food to seedlings, and they do it by making use of the so-called mycorrhizal network that results from these connections between roots and fungi.
Unlike the tropical tree-living orchids you might buy as house plants, terrestrial versions are notoriously difficult to cultivate. But Field and her colleagues managed to grow (Dactylorhiza fuchsii), which are widespread across Europe, in the lab by using a growth medium that included, bizarrely, pineapple juice. They also introduced a fungal network into the medium that grew and connected adult plants to young orchid seedlings, or protocorms.
The researchers then exposed the leaves of the adult plants to radiolabelled carbon dioxide, a form of the gas that is easily traced as it is metabolised, but blocked it from directly entering the growth medium, the seedlings and the fungal network.
After letting the plants grow for 48 hours, the team measured the carbon in the system and found that radiolabelled carbon was present in the seedlings as well as the adult plants, demonstrating that the adults had used the labelled carbon to make sugars by photosynthesis, which were then supplied to the juveniles.
The work echoes the concept of a 鈥渕other tree鈥� and the 鈥渨ood wide web鈥� 鈥� the idea that trees and other plants communicate and share resources through an underground mycorrhizal network. This concept has taken a scientific hammering recently, with suggestions that the evidence for some claims is lacking.
But at the University of Alberta, Canada, who has criticised some of the claims around the wood wide web, says this orchid work does demonstrate carbon transfer through a common mycorrhizal network.
It remains to be seen which entity, if any, is in control of the transfer of compounds, though. As we learn more about fungal-plant interactions, we may find that language relating to human behaviour, such as competition and sharing and parental care and nurturing, isn鈥檛 appropriate.
鈥淐an the green plants 鈥榥urture鈥� juveniles if carbon allocation to juveniles is under control of the fungus?鈥� asks Karst.
鈥淔ield studies 鈥� which are really difficult in common mycorrhizal networks 鈥� are now needed to find out if speculation about 鈥榩arental nurture鈥� in plants can be justified,鈥� says 聽at Imperial College London.
New Phytologist
