My first Beekeeping class this evening! I’m very excited and plan to report in full.
I realized that with all the soil (clay) we’ll be digging up to create the pond, we’ll be able to make an earth oven. There might even be enough to build a small adobe structure around the oven. We’ll just have to lug it all up the hill…
I also realized that I might have to hold off on buying the elderberry and blueberry shrubs, because chances are we won’t have their part of the garden (the flower garden up front) prepared by the time they are shipped. But I do have a wonderful space in mind for one or two hardy kiwi vines, and I’m sure I’ll be able to get that ready.
Be sure to scroll down to Part 7 of the Calcium in the Soil and Plant series.
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.
Last year’s averages (calculated here) are mentioned as a baseline. I use this calculator.
Gasoline. This is the usual: still too high. When the temperatures go up I’m really going to work on biking Amie to school and back.
9.52 gallons per person (pp) in cars + 10 miles pp on public transport
= 23 % of the US National Average
(Last year’s yearly average: 24.8%)
Electricity. This went up a little because of the confluence of four things: we’re using the space heater in the bathroom more often, our new fish tank requires heating and filtering, we’re using the humidifier in our bedroom at night, and we’re internet-backing up our humongous desktop computer, which we use only for data storage (it’ll take 2 weeks this first time around!).
445 KWH (all wind) = 12 % of the US National Average
(Last year’s early average: 18.2% – we only switched to wind in the middle of the year)
Heating Oil and Warm Water. It’s been cold. Again. We heat to 58F at night and most of the day. The wood stove goes on around 4 in the afternoon and goes till when we go to bed – seems like, as soon as the sun goes down, our tolerance for 58F comes to an end. With the stove I try to keep it around 64F. Our first cord is finished now, so I’m adding that (it was used over the last three months or so). Our warm water too is heated with oil.
71.4 gallons = 116 % of the US National Average
add 1 cord of wood: 140 % of the US National Average
(Last year’s yearly average: 77%)
Trash. We’re holding steady on this one.
5 lbs pp = 4 % of the US National Average
(Last year’s yearly average: 7.3%)
Water. This went up by a bit from the usual (14 %). Don’t know why.
443.8 gallons of water pp = 15 % of the US National Average
(Last year’s yearly average: 16.5%)
Consumer Goods. We purchased next to nothing this month. All I can think of are four little fish ($1.25 each) and fish food. (I’m, as always, excluding seeds and growing supplies.)
$15 = 8 % of the US National Average
(Last year’s yearly average: 27.2%)
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It’s interesting to compare these last three months to the same months last year, to see what a difference our wood stove and the lowering of the thermostat are making in our consumption of heating oil (so I’m not reckoning in that finished cord):
Nov 2008- Jan 2009 (63F): 131.6 % vs. Nov 2009 – Jan 2010 (58F): 82.6 %
We had, of course, that crazy warm November in 2009… Still:
Dec 2008 – Jan 2009 (63F): 155 % vs. Dec 2009 – Jan 2010 (58F): 112.5%
It’ll make a noticable difference in the yearly average. If only we could eliminate the part of the oil that goes to heating our water, if only on warm days.
