MamaStories

One of my ambitions is to make a phenology of this place. I’d love to use many media. Words foremost, then drawings, paintings and photographs, and  occasionally audio recordings and videos (but those I wouldn’t be able to stick in my favorite “container”, the book). To make a little drawing every day, of the newly arisen chipmunks, a flock of Robins, the daffodils finally poking through or the flowering buds on the bushes?

In any case, it’s not going to happen today, or tomorrow. Though a wonderful day, the first day of Spring, I should say, the only time I made it outside was to release three more mice (the full count is up to 10 now). Also got the Mama mouse this time, so perhaps it will be the end of them! They got themselves trapped but not before eating half my tomato seedlings. And there I was, yesterday, gleefully entering “100% !” in the germination chart for nearly every one of them. I resowed.

So last year the garden was weather-doomed (”dimmest summer on record”, wet and blighted). This year will be pests and varmints? Wish we could get all the plagues over and done with in one year (i.e., last year)!

So why didn’t I get out there? Amie has caught a bad cold and she (and I) got no sleep last night, and today she spent on Mama’s lap, hip, or shoulder, and then next to Mama taking a long nap (Mama too!). I did love the way the sunlight flooded our bedroom, so bright and warm as I drifted off to sleep.

Hopefully I can get out there tomorrow to do some surveying, bed and hoop house cleanup, compost turning, and perhaps even some tucking in of peas and favas.

I heard the sound again and this time we ran out to record it. It was further away and it sounded a little different from last time - less catlike - but though the “words” are different, the voice seems the same (to the one in my memory). In any case, if you can tell us what it is, if not a fisher cat, let us know!

animalsound

You guessed it: it’s time for another episode in the Calcium in the Soil and Plant series! Take heart: we’re getting close to the end (maybe only one more part to go?). Actually, it took me so long to post on this again because this one took me a long time to figure out. If you want to brush up on the previous parts, check out this page.

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Part 8. Selective Nutrient (and Water) Uptake by Roots

Nutrients arrive at the root surface in three ways:

1. The first of these is root interception. As roots grow, they make direct contact with nutrients. This mechanism is less important because roots come into direct contact with only 1-3 percent of the soil volume exploited by the root mass. Mycorrhizae – fungi that form a symbiotic association with plant roots - can increase the surface area that roots can extract nutrients from. Calcium and magnesium, because they are so abundant, are often intercepted by root contact.
2. The second mechanism is mass flow, wherein plants, sucking up water (through the various pumps and pulls discussed in the previous part), also move the nutrients that are dissolved in it. Especially mobile (free) nutrients are “attracted” in this manner: nitrate-nitrogen, chloride and sulfur, which are never absorbed by the colloid and thus always exist in solution, and calcium and magnesium, which are held only loosely to the colloid. The drier the soil, the less mass flow.
3. The third mechanism is diffusion, by which ions in the soil spontaneously move from a point of higher concentration to a point of lower concentration (like in osmosis). Diffusion happens in the soil because the immediate root area, once it is depleted, has a lower concentration of the nutrient ions. Immobile nutrients like phosphorus and potassium, which have a low solubility, are strongly held by the colloid, and are only present in small concentrations, reach the root through this mechanism. The soil porosity is important here: smaller pores will block diffusion.

The last two mechanisms are the more significant mechanisms of nutrient uptake. Which one is predominant depends on the nutrients, the amount of water in the soil and the physical conditions (e.g., crumb structure) of the soil which dictates the movement of water through it.

Nutrients (especially immobile ones) then need to be wrested from the colloid by an ion exchange – the cation exchange capacity (CEC) talked about on a soil test. As we saw, the positively charged nutrient cations are held to the negatively charged colloid by a small electro-magnetic bond. When the root hairs release hydrogen ions (H+) and these come into contact with the colloid, they take their places on the colloid, breaking or weakening the colloidal-nutrient bond. The nutrients are knocked free and this makes them more available to be taken up by the root hairs.

Once the nutrient has arrived at the plant root surface and has been made available, the root needs to take it in: the nutrient-ion needs to travel from the root’s exterior to its interior.

As we saw in Part 7, the membranes of the cells making up the epidermis and the endodermis of roots are semi-permeable. This means several things. First, roots allow movement in, but not out, which allows osmosis to take place, by which water is taken up by the plant roots (cf. Part 7). Second, they allow only small solutes in, so they are impermeable to the large molecules of organic solutes (more about that in the next part). Third, some small solutes are allowed in, but others are not: plant roots are selective about their food.

It is the last aspect that interests us here. The uptake of the nutrients (as well as sugars and amino acids) by the roots is selective because of two main features:

1. First, the root membrane has channels that are ion-selective: one type of channel will let through only phosophorus ions, another fits only calcium ions, or potassium or nitrate, etc. Think of the toddler’s toy: the box with the star and pentagon and circular shaped holes into which only the star and pentagon and circular blocks fit. The root too is constructed like that.
2. The actual ferrying through these channels is done by ion-selective carriers: so-called coupling proteins that are embedded in the membrane of the root cells and that only react with specific ions, passing them on. Different plants require different amounts of nutrients, and so they will have different types and densities of ion carriers on the surface of their cells. These ion carriers are also most numerous on the surface of root hairs and root tips, which shows that roots are the main conduit for nutrient uptake in plants.

That explains the root’s selection of particular nutrients. Now, how does it select their quantity? How does it say, that’s enough?

As for water, its protein carrier is the aquaporin. Aquaporins are embedded in the cell membrane, forming transmembrane pores that conduct just water molecules. They prevent the passage of ions and other solutes by a filter (the ar/R filter) of amino acids that bind only water molecules and let them in (single file), while excluding all other molecules. When there is a lack or an excess of water, a gating mechanism changes the shape of the aquaporin so that it blocks the pore and stops the water flow. These gates can fail and an excessive amount of water can break the gates, as it were, and “drown” a plant.

Nutrients like calcium ions are taken up by different transmembrane protein carriers, which actively transport them, that is, they require energy to do so, because they have to pull in ions against their concentration gradient. For instance, there’s a good chance the root cells already have a higher concentration of calcium than the soil in the root area, but it might still need more. The energy required comes from a part of the cell (called the ATP, a nucleotide). If the plant has enough of a nutrient, it can simply stop drawing on the energy source. Also this mechanism can fail, and an excess of nutrients can lead to a toxic overdose and kill the plant.

So, however well-equipped roots are to select what the plant is in need of, it is still up to us, gardeners, to know how much of what a certain plant in our care needs and how much of it is present in our soil.

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Next up, nutrients not in mineral but in organic form, and how those can make it into the plants. Yes, the egg shells. Finally!

This time of year I get that lump in my throat. I see my seedlings come up in the basement. I do the rounds of blogs - mostly gardeners, homesteaders - and see their seedlings come up as well. It touches me deeply. It is a reawakening of a childlike feeling of wonder, that, with only the addition of water and light, life comes out of such a tiny seed.

But hold on. Maybe children, I assume, have that feeling of wonder and it comes naturally to them. It fits them. I see that in Amie sometimes. ‘Wo-ow!’ she says, and moves on. For me it is less wonder than awe. There is something menacing in it, something too big. Hence the lump in my throat and sometimes - I admit it - a tear in my eye, at the sight of a seedling. Has my soul shrunk, in adulthood, so it can no longer hold that great capacity of wonder?

If so, I am flexing its boundaries!

I am so lucky to have the opportunity to live here, where I can grow food from the miraculous seed, and watch the awesome wildlife, and feel the great mycorrhizal colony underneath my feet, and untie- undo - my soul.

Set 2 traps with peanut butter. Waited 1 night. Found 3 mice. Amie and I released them 1 mile away.

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Resowed all the seeds (onion, celeriac, lettuces, spinaches and chards). Lovage,  Common Mint and Pennyroyal are germinating well. The celery also escaped and I can now call them seedlings.

Friends are coming to visit for a couple of days, and I doubt I will have the time, or the inclination, to interrupt the fun we always have to post here. But before I go, a few notes:

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Turns out that the bobcat I heard a couple of weeks ago was most likely a fisher cat. My neighbor saw one crossing the street this morning and immediately fired off an email to let me know. And it clicked, because Suldog had raised this possibility in his comment to my post. Apparently fishers make that haunting sound during mating season, though they’re also know to make it when they’re trapped or attacking. No bobcat, then, but pretty wild anyway!

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I’ve signed two petitions in the last two days.

1. One for allowing chickens in Cambridge, Mass. (there’s a blog article about it here, and the petition is here).
2. The other for allowing the sale of raw milk by a dairy farm in Framingham, Mass (about raw milk in Massachusetts, click here, and here, and to sign the petition, click here).

There’s a Food Revolution and I’m on it!

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I totally missed the “Focus on Feeders,” which the Mass Audubon Society organized this year on 6 and 7 February. But I am thinking about sending one or two photos to their amateur photo contest. Here’s a selection (click for larger):

They are: Black-Capped Chickadee, Tufted Titmouse, Rose-Breasted Grosbeak, Downy and Hairy Woodpecker side-by-side, female Northern Cardinal and Red-Breasted Woodpecker (photo taken yesterday).

I like the first two because of their wintry atmosphere: the birds seem cloaked in the snow-laden sky. The Grosbeak was such an exception at my feeders, and I love the color of his breast. The Hairy Woodpecker (the large one) is so darn ugly; even his eye looks scruffy! But it was great to see the two kinds side by side. The female Cardinal gives us such a stern look, and look at the soft colors of her belly. And that last picture is just so vivid.

Do you have any favorites?

So this happened half an hour ago, at 10 pm.

I’m sitting in my living room, working on the laptop. Suddenly there is a racket in the street. A small dog barking very, very loudly? Surely that’s not a dog? I go outside with my flashlight. It’s 10F and I’m wearing a skirt and a thin sweater and my breath is almost obscuring my vision, but the first new yowl I hear sets my whole body on fire. Hair-raising. Repelling, but oh so magnetic too…

I see two dark shapes moving across the street, about 40 yards away, down the hill in and out of the bushes. A large and a smaller shape. Cat like movements. And that cry: a short, repeated scream from one of them.

My street has no street lights, but there are some small porch lights - I wish it was one of those crystal clear full moon nights we had a couple of days ago. Then I see the eyes: two large yellow eyes sharply reflecting the light from the neighbor’s porch, and perhaps my own flashlight. A pair of smaller yellow (or was it white-bluish?) eyes right behind it.

By now, curious, drawn in, I’ve moved about 20 feet outside my door. The lit eyes disappear and I lose sight of their dark shapes. The screaming too has stopped. They’re invisible, who knows where, and I realize I’m easy prey - no really, that was my realization, here, in a Boston suburb!

I run inside and close the door.

It was this sound, the first one on that page. A lynx or bobcat, maybe a mother and her young.

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It was exactly around this time year that I heard the Great Horned Owls singing to each other behind my house. I’ve not heard them yet. The world is full of wild creatures, reminding us of what we are not. How good it feels, to be reminded!

This is already the seventh part in a series on how calcium and other nutrients get into the soil and then into plants. Here we finally meet the plant roots, and investigate how they take up water. Click to read part 1, part 2, part 3 and part 4, part 5 and part 6.

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7. Water uptake through osmosis, turgidity, root pressure and transpirational pull

I’ve given so much attention to the solubility of calcium in water because plant roots can take up nutrients only if they are dissolved in water. Let’s stick with the water for now and add nutrients in part 8. How do plants take up water?

The surface of root tips are made up of epidermal cells (epidermis = outer skin) and their extensions, called root hairs, which form a fuzzy band and increase the absorptive surface area and thus the rate of water uptake several hundredfold. These surface cells and hairs draw water from the soil by osmosis (Greek osmos = a push).

Osmosis happens when there is an unequal concentration of solutes in the water on either side of the epidermis. On the outside, the soil water consists mostly of water with a small amount of salts (any dissolved ions - see part 5). On the inside, the epidermal cells contain water with a much larger concentration of salts, sugars and other substances. The water in the soil seeks to dilute the water inside the epidermal cells, and it pushes, through the epidermis, into the root. The epidermal cell membranes allow this free movement, but only in this direction. If outward movement were allowed, this system would not work, and the root would lose its precious salts and sugars.

The water is stored in the vacuole of the cell, making it turgid or swollen. When the vacuole is fully inflated, the water uptake will slow down, because the internal pressure or turgor inside the cell will squeeze the water out to the next cell, and so up into the rest of the plant, to where it’s needed. You see this effect when you water a wilted plant: slowly all its deflated cells are filled with water through turgidity.

This explains what the problem is with excessively saline soils (see part 5). Even if there is enough water in the soil, it is not diluted enough, and so the inequality between it and the water in the root cells is not large enough, to achieve strong osmosis. Even worse, there might be less water content in the soil water than in the root cells, which reverses the direction of the osmotic flow. Deflated of their torgur pressure, the plant will wilt and, if this continues, die.

Cross section of a plant root
(image from Capon, Brian, Botany for Gardeners, Timber Press, 1990, p.141)

Water constantly circulates into, through and out of the plant. This happens through two specialized vascular tissue systems that run up and down through the entire plant. One is the xylem tissue, which carries water and solutes, and the other is the phloem tissue, which carries mainly organic nutrients, like sucrose. We’re interested in the xylem, which is situated at the center of the root.

To get the water from the epidermis (outer skin) to the xylem, it has to cross another boundary, the endodermis (= inner skin). The endodermis is a second osmotic pump, adding to the pressure (but I’ll return to this one in part 8, because it has to do with how nutrients are taken up). The epidermal and the endodermal osmotic pumps together create root pressure, which moves water (and nutrients) from the root tips to the tips of the leaves, through the xylem.

But just root pressure is not be sufficient to pump water all the way up into the branches of high trees. A second system is necessary for this, called transpirational pull. As the terms suggest, root pressure is a pushing (up) force, from roots to leaves, whereas transpirational pull is a pulling (up) force, from leaves to roots.

Very simply, transpirational pull works like this. Water molecules cohere together, forming an unbroken string or column of water in the xylem, all the way from root tip to leaf tip. When one water molecule is lost at the surface of the leaf through transpiration, or evaporation, the next water molecule is pulled up, along with the whole string of molecules. At the bottom, the roots get to suck fresh water from the soil.

And not just water, of course, but also the nutrients that are dissolved in it. Plants are, however, selective in what nutrients they will allow in: they won’t take up what they don’t need. That in the next part.

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I foresee one more part. Maybe two. But I keep an option on three.

O, that egg again!

We’ve arrived at Part 6 if this extraordinary saga of how calcium arrives and behaves in the soil (if I’ve occasionally typed “soul” instead of “soil”,  is it really a typo?). Click to catch up on part 1, part 2, part 3 and part 4 and part 5.

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6. Soil base saturation and soil pH

The term “soil acidity” expresses the quantity (expressed in meq/100g) of the acidic cations (cf. part 3) that the soil can hold on to. The percent base saturation – another important term on your soil test results - is the percentage of the soil’s cation exchange capacity (CEC) occupied by the basic cations.

This is from our soil test:

This means that calcium occupies 50.6% of the total exchange sites. In other words, in 100g of my soil, 15.6 meq can hold on to cations, both basic and acidic. Of that, 7.9 meq is occupied, or saturated, by calcium, 1.65 meq by magnesium, 0.64 meq by potassium. So, as far as I can learn from the test results (*), 10.19 meq/100g of soil, or 65.3% of the CEC, is saturated by bases. That leaves 35.3% of the CEC (*) for the acidic cations (hydrogen and aluminum).

(*) Sodium (also a base cation) is not listed on my test results, which means its levels are low, so I don’t have a sodic soil (cf. part 5).

Not surprisingly, the greater the percent base saturation, the higher the soil pH. Because calcium is normally the major cation, by virtue of its abundance taking up about half the CEC (as in our soil), we can say that there is less calcium in acid soils and more in alkaline soils.

But if the soil is very alkaline (pH > 7.0), the high levels of calcium may have negative effects. For one, more calcium taking up the CEC very simply means that there is less room on the colloid for everything else. Secondly, an excess of calcium can no longer be adsorbed onto the colloid. This “free” or unadsorbed calcium begins to accumulate in the soil water and goes on to react with what other nutrients are present.

For instance, the free calcium will readily attract soluble boron (B-), which is an an-ion (a negatively charged ion), and form a nearly insoluble compound with it, thus making the boron less available to plants.

Excess calcium will also tie up, or immobilize into insoluble compounds, cations like iron (Fe++), phosphorus (P+++) aluminum (Al+++), zinc (Zn2+), copper (Cu2+), cobalt (Co2+), and manganese (Mn2+), as well as magnesium (Mg ++) and potassium (K+).

Lastly, calcium also increases the pore space in the soil by flocculation, which, as we saw in part 5, is desirable. But when pore space exceeds 50% of the total soil volume, the soil can dry out much easier, like sand.

In short, too much calcium in your soil and many nutrients become insoluble and thus unavailable to plant roots, and the soil structure is damaged to boot.

But, on the other hand, if the soil is very acidic, and thus if there is not enough calcium, many of the other cations can become excessive and thus toxic. Then calcium applications with limestone are called for. The aim when attempting to adjust soil acidity is never so much to neutralize the pH as to replace lost cation nutrients, particularly calcium.

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Next time, I promise, we’ll finally meet the plants, and discover by what magical means they get the calcium out of the soul soil.