Bryo-eating mites?

In my last post on growing bryophytes in takeaway boxes, I said that my bryo cultures are not axenic monocultures. A good example is my tub of Mnium hornum, shown in the photo above, which has turned into little ecosystem.

Last summer, I collected a small clump of M. hornum from the base of a beech tree. When I inspected it at home, I found that most of the shoots were missing their tips as if they had been bitten off. Since then, I kept the clump on a pellet of damp compost. Without tips, the shoots did not grow any further. Over time, they dried and turned dark green/brown. These are the shoots in the centre of the pellet shown above. But as you can see in the photo, there has been much new growth since then – new shoots that developed from rhizoids. These young shoots look slightly different to mature M. hornum plants. The leaves are somewhat shorter and look more triangular. They are not as strongly toothed as on mature plants. Also, the leaves are rather light-green possibly because they get less light in my bryo shelf than they would get in nature.

On the older (decapitated) plants, I soon discovered small white flecks (photo below). At 30x magnification, these flecks turned out to be some flaky substance and I still am not entirely sure what they are. First, I thought they were a fungus breaking down the dying moss tissue. These flakes are only ever on top of leaves, no matter whether they are curled bottom side up or not. It looks like they may have dropped onto the leaves. Droppings of some animals?

Around the time I noticed these white flakes, I also noticed translucent mites roaming several of my bryo tubs. The fact that these mites have green body contents suggests that they eat some plant matter. It does not look like they like live moss plants – there are hardly any visibly damaged leaves in this culture. The mites may feed on protonema, on which I often see them, or they may eat algae that also grow on my compost substrate. Here’s what they look like:

Sometimes, I find mites in between the top leaves of M. hornum plants, and I suspect they may occasionally eat the vegetative tip of a shoot, effectively killing it off. Still, there are plenty young, happy-looking shoots, and I am not going to intervene for the time being.

Additional cryptogams

In addition to these mites, other plant species have appeared, too. On the side of the compost pellet, a thin, frilly structure has appeared. A frillwort? I think that members of the liverwort of the genus Fossombronia look similar to this. Upon closer inspection, I noticed little hair-like structures perpendicular to the frilly surface. I think now that this may be a fern prothallium, the haploid life stage of a fern.

Also, there are two more species of moss. The first bears bulbils and seems to have separate sexes. I reckon it is Bryum dichotomum.

Bulbils/little plants scattered on a protonema felt. This is also one of the mites’ favourite spots and I wonder whether they feed on protonema.

Tips of two larger shoots. The bottom-left one has a terminal perigonium, a male “inflorescence”, with clearly visible antheridia. Almost like a little nest of Easter eggs.

A dissected (or butchered) perigonium under the microscope. Gherkin-shaped antheridia are mixed with paraphyses (hairs that stand in between the antheridia in the perigonium).

The second moss is Bryum pseudotriquetrum, I think. It has got leaves about 5 times as long as wide. The leaf margins consist of cells that are long, thin, and clear. The leaf margins run down the stem. Stem and costae are reddish in older plants. The costa runs up into the leaf tip. The leaves are translucent with longish-hexagonal cells (mid-leaf).

These two mosses have popped up in others of my cultures, too. I wonder whether they grew from spores present in the compost, whether moss spores are so abundant in the air that they may just drop into my tubs, or whether it’s me who introduced them. I might set up a tub with only compost and see how it develops.

You may have noticed that this culture is growing on a black lid. This is because I have started turning yoghurt tubs into growth containers for smaller bryo cultures. Takeaway boxes are a nice size, but I am now running out of space on my shelf. Next time, I’ll talk about how I made them.

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