At Most Spheres

Sphere is more than a mathematical concept. In biology, or more precisely ecological microbiology, it is devoted to those special places of biological interactions, usually between plants and microbes. I can’t tell if other sciences use -sphere this way, but it seems like specific sociology or psychology subfields do, and we speak of blogosphere too. Interactions is an important part of our sphere concept.

The very first time I stepped into a biological use of a sphere was with rhizospere, as a student. That’s basically a place near roots where plants interact with bacteria and fungi. Not so surprisingly, if plants can change the nature of that place, they can change interaction and thus the nature of this community. And it does, they simply have to secrete secret chemicals, usually sugar to start with, and the whole microbian community will change. Not that tricky to evolve, and of course, natural selection is opting for secreting the chemicals that promote benecial interactions (or less harmfull interactions, because you may also try as a plant to get rid of pathogens and herbivores).

Then, and as a words lover, I was delighted to read a whole bunch of spherical words in a paper recently*: cormosphere, caulosphere, calusphere, phyllosphere, anthosphere, and carposphere (and let’s add spermosphere). A straightforward definition is used in that paper, so I just quote:

The cormosphere is the microecosystem consisting of the plant surface and its immediate environment; it is the region of exchange between biotic and abiotic components. It is composed of the rhizosphere, caulosphere, calusphere, phyllosphere, anthosphere, and carposphere. Caulo-, calu-, antho- and carposphere refer respectively to the surface of the stem, bud, flower, and fruit.

Only the spermophere is missing, and that’s just that interaction space involving seeds and its communities. Important too, since some plants require specific interactions right on start else they don’t germinate (think of orchids and their mycorrhizae).

See, that’s convenient to refer to these spaces, because you might be specially interested in specific interactions or specific communities, and every now and there, plants parts have their specific chemical compositions, locations, and nature of exudates (exudates** of course stands for secreted chemicals, not previous attempts at finding a mate). So you’d expect different microbial communities at these varying spheres.

I’m not going to tell anything more about that, but instead investigate the use of these words in research past (I’ve become fond of that way of writing). Please handle with kid gloves, as there are at least two issues for the record. First, given only word lords will craft manuscripts with such emotionally loaded terms, a great number of studies will not be found but still address such specific interactions and be gone with the wind. I won’t try to count them. Second, I make the hypothesis that the number of word lords is proportionnally the same in every subfield addressing these, so that documented variation reflect variation of interest among scientists. Maybe that’s just plainly wrong. I just think that’s not.

So I played with google scholar a bit (I like), and here are the number of hits for each of these lovely words:

– cormosphere: only one science paper, the one cited above.

– rhizosphere: 151 000 hints (449 for 2013 already!).

– caulosphere: 46 hints (none in 2013 yet).

– calusphere: only one science paper.

– phyllosphere: 9 560 papers (33 for 2013).

– anthosphere: 27 hints (none in 2013 yet).

– carposphere: 117 manuscripts (1 in 2013 already!)

– spermosphere: 1 760 hints (3 in 2013 already).

Hum, there’s a reason why I learnt about rhizosphere first, other sphere more than 10 years later… Tells us plants- or microbiologists are really into the business of understanding interactions between plants and other smaller worlds at roots and leaves. Not so striking. But if you’re willing to dig a niche in microbial ecology, you might as well begin investigating organisms that strive on stems, buds or flowers!

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*The paper is not recent, I just happened to read it. Maybe I already read it, as it had awaken strange memories, but that was before internet. It’s this one:

G Ende, and H F Linskens (1974). Cutinolytic Enzymes in Relation to Pathogenesis.  Annual Review of Phytopathology 12: 247-258.

** Strikingly, there’s only a letter difference between English and French’ exsudate.

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