A maple leaf is more than it appears to be. Its substance is made not just from plant cells, but from a community of many species. “Maple” is in fact part plant, part fungus, part bacteria. Just as the human body is comprised of a vast “microbiome,” plants are also composite creatures.
To get a glimpse at this diversity, I cultured some of the fungal species found on and within the maple leaves growing on the tree by the front door.
To look at the fungi on the leaves’ surfaces, I dabbed maple leaves onto pertri dishes containing agar and fungus food, then waited a few days. Here is one such dish, displaying the diversity of species found on the leaf. Of course, many fungi don’t like petri dishes, so what we see below is a mere fraction of what is actually present on the leaf. The leaf itself is not so thickly coated; the petri dish gives fungi a place to grow and reveal themselves to our eyes.
These fungi from the surface are a mixed bag. Some are potentially harmful to the leaf and will ultimately eat the leaf away when it drops in the autumn. Others are likely protective or live as commensal squatters. Some feed on the droppings of caterpillars or the honeydew of aphids. A few might have drifted from the humans, goats, and stacked firewood below.
To peek at fungi that live inside the leaf, “endophytes,” I sliced some leaves into tiny pieces, sterilized their surfaces, then placed them onto petri dishes. Compared to the leaf “prints” taken from the surface, it took a couple of days longer for these endophytic fungi to appear on the dishes, but they too showed quite a diversity of forms. Here are two examples:
To make sure that I was not simply growing fungi that were wafting in the air or present on my forceps, I also ran some “control” plates which yielded either nothing at all or a few white blobs.
How endophytic fungi interact with tree leaves is largely unknown. But one of their roles is protective, secreting substances that deter the growth of pathogenic fungi. For example, endophytes isolated from Douglas maple release a chemical that poisons a variety of nasty plant diseases.
Interestingly, endophytes in sugar maple leavs seem to be more diverse in old growth forests than they are in younger, managed forests, or in urban areas. But these are preliminary findings. We have only the haziest understanding of the ecology of the fungal world hidden within leaf laminae.
Inside each leaf: a whole community. Within the community: hundreds of stories waiting to be heard. One story is clear, though: if we believe that creatures — humans included — live apart from “the other,” we’re deluded.
David George Haskell 
That is cool! :) And weird!
Life is complex to the max.
We pine for simplicity. Why?
Good question! Less taxing for the (themselves complex) nerve nets in our heads?
If I get up the nerve to answer that, I’ll let you know. ;)
No, really. We should want our nerves to be extroverts,
and make as many connections with the big wide world
as is possible. Symbiosis is Nature’s way of making peace.
This is so interesting. Have been thinking lately that this landscaping practice of removing all the leaf litter from beneath trees & replacing it with ground up wood (mulch) from who knows what other species is an interruption of the highly-evolved balance between whatever is in & on the leaves & feeds the roots of the tree with its specific needs when it breaks down in/on the soil.
I continue to be fascinated by the symbiotic relationships between all of earth’s plants, animals, and elements. It seems soo complex if one tries to take it all in at once, but so simple and productive on more finite levels. Thank you for sharing your petri dishes. I did not know about endophytes until now.
Thank you. Always happy to share my petri dishes!
Good point. Heavy layers of exotic mulch do little for biodiversity (and are often harvested from other ecosystems in harmful ways).
Brilliant stuff — both the experiment and its results.
Thank you for another reminder that miracles are all around us — and Mother Nature is always busy, busy, busy.
Hmmmm. This makes me think twice about using leaves as toilet paper while hiking! What do we use now David?
Ha! I’ll bet the leaf gets the worse end of that deal in terms of innoculation. And you are probably enhancing your butt flora. A full woodsy experience. Just don’t then sit on a petri dish for a week.
Mr. Haskell, besides reading and learning from your wonderful The Forest Unseen – by
the way, has that been translated into German by any chance? – I have already learned
something from this site:
…”the honeydew of aphids” mentioned in the fungi article. I googled this and found that
moths also secrete honeydew. I had been noticing some yellow dropletss and streaks walls
and cabinets in our laundry room. Could not remove it unless I scraped with a knife.
We have some moths flying around which originated in a bag of bird seed. A few
days ago I noticed droplets just where the moth had been, the droplets were soft and easily removed. Now, can you tell me how to removed the caked on ones? :-)))
Thank you.
Thank you! No German translation, yet. I’m not sure what to suggest about the stains: if it is honeydew, then repeated washes with water will remove it. If feces, then more vigorous means might be necessary.
Thank you, Whether honeydew or feces, at least I know where it came from :-))
I am in search of those who speak on behalf of mature and older forests being left to move through their natural cycles. There is a strong and powerful voice stating forests must be managed through timber harvesting in order to promote healthy forests and wildlife habitat. I know we need the resource, but where are the academic voices in support for letting “nature take it’s course” ? This isn’t an either/or issue, simply a search to find those who can and will speak on behalf of allowing the forests to manage themselves. Anyone out there?
Thanks!And may the forest be with you!
Copper
Hello, I’m just wondering what temperature you placed the dishes in for the bacteria to grow? also did you seal the dishes once you had dabbed the maple leaf on the bacteria or leave it open to air?I’m composing a similar experiment, trying to grow my own bacteria, hoping to achieve a variety of different textures and colours. Any advice would be appreciated.
If I remember, I cultured at room temp. The dishes were fungal media — malt extract agar and another I think — and focuses on fungus only, not bacteria. For the internal ones, I sterilized in dilute bleach.
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