Photo by Samantha Humphreys
Mosses look ferocious under a microscope with hideous teeth. Good thing they are small, and never known to bite. The teeth, called the peristome teeth, regulate spore release, opening and closing in response to humidity changes. The entire moss life cycle is out in left field, but we can’t do it all today. To take that turn on your own, BITE HERE
So what’s the big deal about that mossy magic carpet? For obvious starters, the rug insulates tree roots, retains moisture, cuts erosion, and sequesters nutrients. No surprise tree roots sometimes congregate under mosses. Moss removal sometimes impacts the trees above.
Mosses are nutrient catchers. Although they can obtain nutrients from soil, they have no roots or veins, and soil-absorption is merely one trick in their book. Mosses absorb nutrients also from direct exposure to rain water, mist, stemwash, dust, puddles, and poodles. Rainwater arrives with dissolved nutrients, and percolating through the leafy tree canopy can enrich the drizzle. Direct nutrition allows mosses to colonize tree trunks, rocks, sand, and other places where others dare not grow.
In Florida mosses love palm and cypress trunks, presumably enjoying the nutrition washing down. Palm trunks are a little spongy. Bald cypress, being deciduous, allows sunbeams down to the moss zone, and in a swamp. Mosses favor swamps. The tips of cypress knees grow above their mossy green jackets.
Mosses hold water for long spells but eventually dry out into suspended animation. They are resurrection plants. Upon re-moistening they pop awake in seconds—repeat—in seconds—experiencing an adrenaline rush plant physiologists call a respiratory burst. In the wink of an eye a remoistened moss starts heavy breathing before photosynthesis takes charge.
Respiratory burst, moss on a palm trunk on the PBSC campus. Horizontal = seconds. Vertical = carbon dioxide released (respiration). Seconds 1-300 the moss was dry. It was soaked with water at 300 seconds. Immediately there is a big burst of carbon dioxide, peaking at around 625 seconds when photosynthesis seems to take over and start using more carbon dioxide than the plant is producing.
Nitrogen is the main nutrient and presumably most limiting. How mosses obtain nitrogen is more subtle than mere manna from heaven. Nitrogen fixation (capture from the air) in nature can involve many species of microbes and associated plants, most famously legumes. Mosses get their fix too. Certain species have symbiotic relationships with nitrogen-fixing photosynthetic (cyano)bacteria. Usually the bacteria live on the surface of the moss. In some sphagnum mosses the bacteria inhabit the hollow leaf cells we’ll discuss momentarily.
Moss in Iceland (by Pat Bowman)
Bear urine and decaying fish are reported sources of moss nitrogen. How about dead bugs? In Iceland expansive rocky or icy areas lie under moss. Where does that nitrogen originate? Reportedly from nutrient-rich geothermal springs, these breeding gazillions of midges who swarm out over the mosslands and become fertilizer.
Icelandic mosses do something even weirder than eating bugs…they form “glacier mice,” rolling stones literally gathering moss. A small stone on the surface of a glacier can grow a covering of moss. It blows around, the mossy covering resisting freezing to the ice. The expanding mouse becomes a rolling planet inhabited by invertebrates: springtails, nematodes, and tardigrades. Probably the microinvertebrates among the moss leaves help churn nutrient turnover. Does the wandering mouse sweep up dead gnats as it rolls? That would be active hunting by a plant! Beats a sedentary Venus Flytrap any day!
Springtails, nematodes, and tardigrades…oh my…are typical moss-dwellers most anywhere mosses abide. The invertebrates dry out with the moss, and everybody slumbers until it rains again. Tardigrades look under the microscope like 6-legged bears, and are called “water bears.” Mosses are their most famous habitats. Tardigrades may be the toughest animals on earth, having extreme tolerances in terms of salinity, drying, freezing, heat, and more.
Tardigrades alter their DNA when they go into their suspended dry phase, and upon resurrection they repair their DNA. It seems that millions of years of DNA repair has perhaps allowed genes from bacteria, fungi, and plants to enter the tardigrade chromosomes. Some of the tardigrade indestructability comes from the microbial genes they’ve adopted. There are more creatures. Mosses host nematodes, and mites that look like micro-crabs.
Springtails abound. Springtails are jumpy little insects primitive even by insect standards. They pay their dues for a happy hoppy home by shuttling sperm from one moss to another. The plants put out scents that influence the spermy little varmints, harnessing their hopping ever-so usefully.
This springtail came bounding out of a moss during preparation of today’s blog.
How does a moss make a monospecific lawn? To begin with competition is reduced in mossish extreme habitats. Many can creep and root, and they propagate from broken bits and pieces. Spores repopulate the carpet continually. Some have microscopic breakaway clonal units to go forth and multiply, and even lie dormant like seeds in the soil. Sometimes ants help with relocation. Mosses suffer little pest damage. Their anti-pest poisonous ways extend to inhibiting other plants. Sabotage is a good way to reduce competition.
Moss carpet in VA. (By Pat Bowman) Probably under a foot of snow tonight (both of them).
Perhaps the most familiar moss to humans is sphagnum. It is the peat of bogs and peat moss. It is where mummified pickled people turn up. It has served as bandages and diapers due to absorbency and antibiosis. Peat is a staple in horticulture because it breaks down slowly and is extremely water-retentive. The ability to hold water comes from a network of big empty cells, each having a small opening. The cells fill slowly and empty slowly, like holding a soda bottle underwater.
Sphagnum. Green cells mixed with empty hollow cells.
You may have gotten this far feeling that mosses are cute, or primitive, or maybe fun to grow. All true. Nice little plants. But don’t belittle a moss, for it may help us keep our cool. Consider this, sphagnum is super-abundant in parts of the globe. Peat bogs tie up enormous quantities of carbon dioxide. Biologist Chris Freeman at Bangor University is advocating a GMO sphagnum able to fight global warming. What will they think of next?