What’s growing in the area: Iris, grasses.
In my yard: Snow covered everything yesterday.
What’s blooming inside: Aptenia, bougainvillea.
Animal sightings: Rabbit out early after Sunday’s snow, but not yesterday.
Weather: Snow last Sunday took down the power for more than an hour; hail and snow Friday; both storms accompanied by thunder; 12:12 hours of daylight today.
Weekly update: When I was child, my natural world consisted of flowers, trees and grass. I knew there were more primitive plants that had evolved before the earth had dried, but I only knew them as algae, fungus, moss and ferns. Whenever I saw them, they looked alike, and whenever I tried to learn about them, they were too alien to comprehend.
Two weeks ago, when I was walking in the arroyo, I noticed what looked like lumps of dried manure between chamisa bushes in the wide sandy bottom. I didn’t remember them from last summer, but dismissed them as bad memory, poor observation, or some effect of rain and snow. Last Saturday, some had turned green.
I’d been told moss was so fussy about water and shade, it would only grow on the north sides of trees in Michigan, and here it was in the open, in arid New Mexico. And, not just in the arroyo: I saw a large patch among the grasses on the bank and found a little on the west side of my garage.
Actually, what I saw wasn’t just moss, but an entire ecosystem of visible and invisible plants above and below the surface, including types of blue-green algae now called cyanobacteria that permeate the soil to create a protective crust. Moss spores settle into the crevices they create.
During dry periods, the biological crust appears as a darker area on the soil surface. In areas like this, where soils freeze and heave in winter, the ground becomes lumpy, while it remains smooth in warm deserts.
All the components of this biological soil crust adapted to changes when lands rose from the sea and green algae became the nucleus for photosynthetic cells in land plants. Mosses are believed to have developed later, in the Carboniferous age of great swamps and reptiles.
Their cellular structure is still so porous their internal water levels adjust to those of their environment. If the atmosphere dries, moss desicates. If water appears, it rehydrates, repairs any cell damage caused by that change, and resumes active respiration within three minutes.
When a dried moss spore germinates, its first cells are capable of photosynthesis. As the quality of light changes and the hormone auxin appears, the green chrononema cells form different, browner cells that spread out from the colony to absorb nutrients. Once the hormone cytokinin is detected, the caulonema cells produce buds that develop into capsule bearing stems.
The rising buds introduce instability that leads the caulonema cells to compensate with cells that anchor the colony. While the rhizoids don’t absorb or transport nutrients the way true roots do, a team at the John Innes Center found that a gene found in the caulonema and rhizoid cells is the one that controls the development of root hairs in higher plants.
The major difference between mosses and their descendants is that mosses are single chromosome plants that produce two chromosome cells only after the buds have developed. Nature elaborated that two chromosome phase until it became the dominant life form, and the single chromosome appeared only during reproduction.
Those more complex plants solved their dessication problem by developing internal vascular systems that can hold water and move it from roots to photosynthetic leaves. Their pigments helped them cope with evaporation, but they lost the ability to survive severe water loss.
Even now, when the earth’s surface is destroyed by man, by mining or by some natural event like a volcanic eruption or arroyo flood, they aren’t the plants that come back. Instead, it’s the so-called primitive ones that make up the biologic crust I saw, for until they create soil by depositing organic matter and the nitrogen they absorb, there can be no higher form of life.
Belnap, Jayne, Julie Hilty Kaltenecker, Roger Rosentreter, John Williams, Steve Leonard, and David Eldridge. Biological Soil Crusts: Ecology and Management, 2001.
Menand, Benoît, Keke Yi, Stefan Jouannic, Laurent Hoffmann, Eoin Ryan, Paul Linstead, Didier G. Schaefer, and Liam Dolan. "An Ancient Mechanism Controls the Development of Cells with a Rooting Function in Land Plants," Science 316:1477-1480:2007.
Photograph: Moss growing on black soil crust near chamisa in the arroyo, 13 March 2010.