Bryolog 5 (1 Sept 2016)
- Election: Ken Kellman is running for Field Trip Director. John Brinda is running for Secretary. Dear chapter members, before 8 November, use this LINK TO VOTE…
- SO BE FREE will be 27-30 March 2017 in and around Sequoia National Park. By 15 December, REGISTER…
- Paul Wilson will give “Bryophytes 101” talk to L.A./Santa Monica Mountains Chapter: Tuesday 8 November 2016, 7:30, at the Sepulveda Garden Center, 16633 Magnolia Blvd, Encino.
- Paul will be giving a similar talk to the Kern County Chapter: Thursday 17 November 2016 at Hall Ambulance Service, 1001 21st St, Bakersfield. Informal plant identification and gardening groups meet at 6.00 pm; Paul’s talk starts at 7:00.
- Along with the East Bay Chapter, we will co-host the December Chapter Council Meeting. Jim Shevock to give banquet talk on Saturday night 3 December. Walks to see bryos in East Bay parks on Sunday afternoon 4 December. Mark your calendars. For updates, <a href="https://chapters.cnps.org/bryophyte/event-updates/.
- It was summertime. People had fun in the fields and mountains. Other people hunched over microscopes.
- We now have 13 liaisons charged with making events happen in cooperation with local chapters. The board plans to increase this number in the coming year.
- Membership numbers are ho-hum for Year 1 (around 80). We definitely want it to grow >100 by the time of SO BE FREE. If you’re not a member of CNPS, please join. If you’re not affiliated with the Bryophyte Chapter, then you can affiliate HERE at no extra cost.
People who know me and who have gone on my winter plant walks have heard me go on and on about mosses. I love mosses. I love mosses and liverworts. These are the fluffy green plants that put a shag on the trunks and drape from the branches of trees in the Pacific Northwest. I like the lichens, too, the plant-like things that put a colorful crust on the bark and give the oak and ash branch tips their gray-green cast in the rainy season.
I like mosses not merely because of how they look. They are pretty enough, truly, especially if you use a lens or microscope, but I like mosses and their ilk as much because of what they do as how they look. There are two special things about them that impress me. One is how they deal with the dry season, and the second is how they deal with the rainy season.
Part One: bryos in the dry season
In a normal year in our area, there is a six-week period with very little rain at the end of the summer. The mosses, liverworts and lichens on the branches of the oaks and ashes out at Mount Pisgah, the mosses in the big trees up in the national forest, will be just as crispy as could be.
These plants are epiphytes and not parasites. Epiphyte means, “upon the plant.” Mosses perched on the branches are attached to the bark but do not penetrate the conducting system of the trees. This is a desiccating habitat, like a bare rock face. It dries anything out very rapidly. One researcher said that a moss growing on bare rock in the sun is drier, on a percent moisture basis, than the USDA specifies for flour on a grocery store shelf. Dry but alive. Mosses, liverworts and lichens on the oak and ash branches are both dry and alive. They are desiccation tolerant.
Most flowering plants and conifers are not desiccation tolerant. Plants like cacti and stonecrops are desiccation resistant, meaning that they store water extremely well so they can last through a drought without completely drying. But if they actually dried out so their tissues were as dry as a moss on an oak tree, they would die. Only about twenty kinds of flowering plants are truly desiccation tolerant.
According to a recent review of the phenomenon, desiccation tolerance was a characteristic of the very first land plants. These appeared in Earth’s history around 500 million years ago. As plants evolved internal water conducting systems they lost the ability to survive desiccation. Apparently this is because moisture-retaining tissue is more efficient at growing tall. The few flowering plants that have evolved (or reverted back to) desiccation tolerance since then have done it at least eight different times. It’s never proven to be a very popular combination—vasculature and desiccation tolerance.
Things are different for mosses and liverworts. They are closely related to the first land plants. Among plants living today, they are most similar to the earliest of land plants. They have retained their ability to survive drying out. This desiccation tolerance is what allows them to occupy microhabitats that the “higher” plants ignore: on open rock surfaces and on branches of trees in climates with frequent, long dry spells.
The amazing phenomenon about these desiccation-tolerant mosses is that they can start their life processes in a very few minutes after they are re-hydrated. Within a short period of time, the cells have absorbed water and started making food. They combine carbon dioxide from the atmosphere with the water and, using the energy from the sun, synthesize sugars. This is photosynthesis, the process of life that gives energy to all living things.
In most vascular plants the enzymes which do this photosynthesis will disintegrate when the cells dry out. These are the desiccation-intolerant plants, those that die when they dry. And this is why desiccation tolerance is so wonderful. Somehow, mosses are able to protect the photosynthetic enzymes in their cells from disintegrating. They are ready to go to work immediately upon rehydration. The cells don’t have to make new enzymes.
Nobody has yet figured out how mosses do this. There’s exciting work to be done in this area. Look for the genetic engineers of the next generation to unlock the secrets of the mosses and put the genes for desiccation tolerance into crop plants. They will be valuable in the drier parts of the Earth. Imagine an annual crop that you don’t have to water. Just plant and wait for the rain. After the soil dries out again, the plants merely shrivel and go dormant instead of drying and dying. With the next rain they’ll spring to life again and grow further until that dose of water is used, and so on until ready for harvest!
What is a fantasy for genetic engineers is a part of everyday life for the mosses on the oaks around us. Step outside and give them another look. ‘Gives you a new respect for ‘em, doesn’t it!
Part Two: bryos in the rainy season
That mosses like wet weather is well understood by Oregonians. Winter is the time of the year when mosses are most prominent; this is when mosses grow the most and fastest; this is the rainy season!
During the dry season, mosses on the branches of trees dry out. They are not parasitic on the trees. The branch mosses cannot get moisture from the host trees. Neither can mosses get essential nutrients from the host trees. Essential elements are to mosses as vitamins are to us: not a lot needed but that little needed is absolutely necessary for life. Some essential elements are easy to get, like carbon from carbon dioxide from the atmosphere. Many others are quite scarce in the environment, especially metals which need to be absorbed as ions of dissolved metallic salts.
Mosses must obtain all the elements necessary for growth from the only source available: the air around them. A certain amount is blown in as dust during dry weather and made available when the dust is wetted by the rain. Then it can be absorbed by the moss tissues. But the nutrient elements present in dust are just as likely to be not ionic and to be washed away by the rain as to be absorbable and absorbed by the plant tissue. Furthermore, there’s not likely to be an adequate supply of essential elements in dust, and it’s hardly evenly distributed over the tree branches. So where in air do mosses get their essential elements? From the rain! The rain that comes from the air around them!
Rain water does not have a lot of dissolved elements in it, but it always has a little. What is special about mosses is that their cell walls have an especially high affinity for the dissolved elements. They are able to pick out what they need and hang on to it. Moss cells use a process called ion exchange to get the rare elements in ionic form. Moss cells literally scavenge essential elements from the most dilute of solutions, even rain water. Any nutrients that come from dust present on mosses and wetted by the rain is also snapped up before it can wash away. In this way mosses get what they need, just enough to grow slowly. Slow growing seems to be just fine for many mosses, liverworts, and lichens.
This ability to scavenge elements from dilute solutions is much better developed in mosses than in vascular plants. That is why mosses do so well in your lawn during the winter. That’s why mosses grow on your roof and not grasses. The winter rains wash away all the nutrients that grasses need to grow, but provide plenty for the lawn mosses to thrive. The special ability to scavenge elements is used against mosses in the Moss Kill formulations people use to eliminate mosses from lawns and roofs. The Moss Kill compounds are salts of metals like zinc and copper. Zinc and copper are actually essential elements for mosses. The special ion exchange capacity of moss cell walls pulls out the copper and zinc they need from rainwater. But when there is an excess of these metals, too much is pulled into moss cells. Too much copper or zinc in moss cells poisons them. Even slightly elevated levels of zinc and copper, harmless to most flowering plants, is toxic to mosses.
The use of copper and zinc to poison mosses demonstrates the extreme ion exchange capacity of mosses. Yet,, hardly anybody mentions that this super ability of mosses might be extremely important to one of our most prominent ecosystems. I refer to the rainforests found along the Pacific Coast from northern California to Alaska.
The rainforests of the Pacific Coast are characterized by the abundance of mosses festooning the branches of every tree and shrub, as well as carpeting every downed log and hillock of forest floor. The mosses are what tell you this is a rainforest. So, are the mosses just there for decoration? Are they there just to take advantage of the situation, because they can grow in rainy forests better than in the inland forests? I think most ecologists have been satisfied to say no more. What they are overlooking is that mosses are an essential component of the rainforests, that the rainforests would not be the forests they are without the mosses.
It’s the rain, remember? Rain which washes away the dissolved nutrients in the soil, away from the roots of the trees and flowers. It is the moss layer of the ecosystem that captures the essential elements from the rain water and fixes them into biological compounds available for all plants of the ecosystem. Where do the essential elements come from? Some arise from the oceans, blown into the atmosphere from sea water during storms. But some, perhaps most essential nutrients probably come from space, captured by rain water from cosmic dust that rains on the earth a rate estimated to be 40,000 tons per year. Every element in the universe is in this cosmic dust.
That’s my theory, anyway. It needs to be tested in detail, but ecologists have verified parts of it to some extent. Mosses are responsible for the nutrient health of our rainforest ecosystems.
And that is, also, why I love mosses.
—David Wagner, Eugene, Oregon
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