The week of 21 September 2013
I step onto the marsh and it announces autumn. Before the leaves of the trees are set afire with an autumnal blaze, before the morning air is tart with a cold bite, scarlet forests of pickleweed are the first to foretell fall’s approach.
I’m standing in the middle of a scarlet forest that extends for meters in either direction but stops abruptly against the taller Spartina alterniflora. Among the golden buttery straw of Spartina I see small flare-ups of scarlet picklweed here and there. The haphazardness of these patches is interesting in this salt marsh, because it has strict patterns of vegetation governed by the tides and competition among species. The scarlet adds a color mosaic to an otherwise monotone palette. The randomness of color is inspired by the gypsy lifestyle that the pickleweed has adopted. It is a gypsy of populations, not necessarily individuals. Individuals have one season to grow, reproduce, and die, making them annual plants (vs. perennials which persist for more than one year). Its shallow root system and short stature (~20 cm) make it a weak competitor, thus it must be able to move on a whim as a population if overrun by superior competitors. To survive on the marsh the pickleweeds must be opportunistic. It is often found in areas where vegetation has been killed by disturbance or stress. This most often happens when wrack – mats of dead vegetation that are carried by the tides – lays on top of living vegetation and smothers it. The vegetation dies and the wrack is carried off by a spring tide (maybe weeks or months later), leaving behind a bare spot in the marsh. For years, large swaths of wrack sat on this marsh, pushed against the levee that is the road by winds and tides, and smothered the marsh. Some of the wrack is now gone and within a season half of the bare patch is colonized by picklweed. This large stand of pickleweed may hold this spot for two years or more, until it is evicted by the deep-rooted and tall Spartinas that march across the marshscape. The dots of pickleweed in the marsh are plants that squeezed in between Spartina neighbors where the canopy thinned and opened up, probably due to salt or flooding stress. These gypsies are not picky where they settle; they know they won’t be there for long.
On another marsh, the foot of the scientist is the disturbance. Each year a path is established to get to sampling locations and each year the path is moved to minimize footfall impact. Now this year’s bare path runs parallel to line of scarlet as the pickleweed have occupied last year’s path.
I kneel down and squeeze a fleshy finger of pickleweed. It’s succulent. Succulence is a strategy used by plants to deal with low soil-water potential, that is, it’s hard to get the water out of the soil. This happens in habitats where the soil water has a high salt concentration when there is infrequent rain (deserts; think cacti) or inundation by salty water (salt marshes and mangroves). To increase the plant’s water potential (i.e., the potential of water moving into the plants) it increases osmotic pressure in its favor by storing salts in its cells. This makes the plant saltier than the soil. As we know with osmosis, water moves from areas of low salt concentration to high salt concentrations.** During a visit to the marshes of Barn Island, Connecticut , my friend Dr. Scott Warren demonstrated the plant’s osmotic strategy. He squeezed the juice from a pickleweed onto a refractometer. 90 parts per thousand (ppt)! Almost 10% salt!**** He pulled out a pocket knife, cut out a bit of marsh turf and squeeze it onto the refractometer. 55 ppt! Aha! So now the plant is able to pump water from the soil to plant passively via osmosis! For reference, marine salt water is ~32-35 ppt.
High salt concentration can disrupt cell function and kill you. Here again, the gypsies are clever to prevent a briny death. One feature that defines a plant as a plant is the presence of a large central vacuole in the cell. These vacuoles are like large storage trunks separated from the cytoplasm and other organelles by a plasma membrane. Plants shove all kinds of things into these cellular trunks and pickleweed stuffs its vacuole with sodium ions. The cell is protected because the salts are safely stuffed into the salty trunk.
It is the saltiness of these cellular trunks that I am currently drawn to now. I pluck a scarlet finger of pickleweed I bite into it. It is soft, but firm and gives a slight crunch, which is why it’s sometimes called ‘glasswort’. It’s salty but nothing that excites my taste buds. Locals tell me people eat on salads but I’ll be damned if I’ve met anyone who has actually done that. The wise internet tells me it is sometimes pickled in Great Britain (perhaps where the name ‘pickleweed’ comes from?).
But tell me pickleweed, why the red? You’ve abandoned your green because you’re breaking down the sun-harvesting chlorophyll as you begin to senesce. You are winterizing. But why the reds? The reds come from your production of a class of pigments called anthocyanins, which come at an energetic cost. Why spend the energy to make these pigments when you’re nearly dead? Maybe you are signaling to grazers – perhaps a hungry salad-eater who needs a salty crunch – that you should be eaten so that your seeds can be carried away?
The pickleweed gives me no clues to this mystery. Perhaps one of you out there know better.
I pluck another red finger, which has many joints called nodes, and break the finger at one of those nodes. It snaps and reveals two white circles. Seeds. The plant will soon loose it’s succulence, desiccate and release its seeds. The seeds are the true gypsy form and they will caravan on the tides until they find their own one inch of marsh soil to call home next year.
**This is why you can kill a snail with salt; the water from the snail’s body exits its body wall to the saltier environment. I can’t believe you did this you heartless bastard. Didn’t you even hear him scream?
****I originally reported this at “almost 1% salt!” because I apparently can’t do math.