Soil and Nutrients

Hi. In this video, we're gonna be talking about soil and the important nutrients found in it. Plants is, you know, produce their own food. They make sugars from photosynthesis, but they still have many nutritional requirements outside of this. So even though 95% of a plants dry weight comes from carbon, hydrogen and oxygen, which they can obtain from CO two and water which of course are essential components to photosynthesis, most plants still need ah bunch of stuff outside of this. In fact, vascular plants require 17 essential nutrients in order to live. Some nutrients are needed in greater quantities than others. Macronutrients are those that are needed in large quantities, and these include nitrogen, phosphorous and potassium. In fact, these nutrients air so important, we often call them limiting nutrients because the availability of these limits the plants ability to grow. And you know, if you think about what these nutrients are used for, you know they go into things like nucleic acids, proteins, boss Philip IDs, essential stuff that any cell needs to exist. Even though micronutrients are needed in smaller quantities, they're still Justus, essential to plants. Life micronutrients include all of these elements you see here and generally they're on, Lee found in trace amounts very, very small amounts. In fact, as the old saying goes, dosage makes the poison. These nutrients can be potentially toxic to plants in high concentrations. That is to say, if plants get too many of these nutrients, it can actually be very harmful for them. Some nutrients are considered mobile and that they could be transported around the plant, while others are called are called immobile nutrients because they're kind of stuck where they are so often when their nutrient deficiencies for a plant, you'll see the old leaves die off, and they do this in order to sustain the young leaves. They're transporting their nutrients to the young leaves and dying off in the process. But this allows the young leaves to continue living in the hope that, you know, maybe they'll be ableto get the nutrients they need. Now, young leaves tend to be the first to show nutrient deficiencies. That is, they're the most sensitive to nutrient deficiencies, and here in this image, if you're curious, you can see all of the different symptoms for the different types of nutrient deficiencies. You might see in a plant those that will become apparent in the old growth and those that will become apparent in the new growth. And, of course, over here it's a nice little diagram of a plant, all the nutrients that are essential to it and, of course, the co thio, H 20 and sunlight that are part of photosynthesis. With that, let's turn the page.

forget everything you see on this page. Guys, soils, just dirt. It's just dirt. So I was just dirt Doesn't matter. That's actually not true. Soil is a highly dynamic composition of inorganic minerals, organic matter, trapped gas, IDs, liquids, mostly water and many living organisms. Soil begins when weathered rock breaks up into gravel, sand, silt and clay. This composes the base of soil soils, then enriched with organic matter. The good stuff is what we call humus. This is decaying. Organic matter usually comes from like dead cells and feces that organisms add to the soil, and this adds tons of nutrients. Now the texture of soil that is, the proportion of components like gravel, sand, silt and clay has a huge effect on plants. It affects the ability of plant roots to penetrate and absorb nutrients. It also affect the ability of soil to hold water and oxygen. And you might not realize what that oxygen is important for. Well, guess what? That oxygen is gonna be the final electron, except er in the electron transport chain of roots so super important, right? Obviously, it's key to cellular respiration, very fundamental process. Now loam is a special type of soil. This is like this is the good stuff. This is This is like the Dom Perignon of soil, right? This has equal proportions of sand, silt and clay with lots of humus. This is like, This is la creme de la creme. This is that good, good soil. Now, when we talk about soil, what we're usually thinking of is topsoil. Because, you know, generally speaking, I don't know how much you dig around in the dirt, but I'm not going that deep. Topsoil is that outermost layer and has the highest concentration of humus and microorganisms. It's usually why it's a lot darker than the layers below it. Uh, it's composed of tons of different organisms, including bacteria, archaea, fungi, algae, nematodes, protests, insects and worms. And those worms. Those guys air super important to soil. They move the soils around, they cycle nutrients, and they break it up to make it better at retaining gasses and water. Now those other organisms also do a ton to help maintain and enrich soil. In fact, we're going to really focus in on what bacteria, archaea and fungi do in later lesson. When we talk about nitrogen fixation so anyways, we talked about topsoil. There's other layers to soil. We call these soil layers, soil horizons, Uh, kind of a funny name. But when you actually see a picture of it, it makes sense, Right? Have you ever seen a like a sunset off in the horizon, Scott? Layers of color, right? Well, here we've got layers of color in the dirt. And this is, uh, you know, this right here is an actual image. You can see that it's about 3 ft down from the surface. That's, you know, in actual picture, Uh, here we have a diagram of some soil horizons that's going to go deeper than what we see here. This is really ending in the subsoil. Um, but as you can see, the soil horizons go deeper and eventually hit what's known as bedrock. That's like rock bottom. Over here, you can see different types of soil compositions of soil textures. This nifty little chart put out by the off federal government, actually, um, kind of cool little chart. Don't worry about, you know, memorizing any of the information they're even really, you know, trying to read too much into it. It's just to illustrate that there's a wide variety of soil textures and this stuff matters right. Our Department of Agriculture, that's who made this try. You know, they care about this stuff because, well, if they don't get it right, you know we don't eat so soil. PH actually varies greatly, depending on where you are, and this can have an impact on nutrient absorption. Acidic soils like you'll find in Conifer forests like forest with lots of pine trees, usually come from lots of decaying organic matter because this decaying organic matter produces organic acids. Now, alkaline soil, on the other hand, tends to be from limestone or calcium carbonate. This limestone, when it breaks down into the soil, will form bicarbonate, which is a week base and but just to be clear, acidic soil. We're talking about low pH alkaline soil. Hi Ph. Just to be crystal clear. Now, soil erosion is when wind and water carry soil away from a place. Uh, roots actually help prevent soil erosion. They help lock the soil in there by sort of creating matrix toe. Hold it in place. Roots also tend to excrete acids, which in general is going to lower soil pH. And you'll see soon why this could be really important. So with that, let's flip the page

plants extract nutrients from the soil is ions. Most of this nutrient absorption is going to occur in the zone of maturation, which is behind the root tip and where you'll find all those root hairs. The reason for this is that root hairs significantly increase the surface area available for water and nutrient absorption. In fact, a single stock of a wry plant, which is kind of just like a wheat plant very similar. A single stock of that can have a root system with the surface area equal to that of a basketball court. Now that's pretty incredible. And it just goes to show how diffuse and how how diffuse the network of roots and root hairs is that it can create that much surface area yet not take up that much volume now. Ions, you might recall, come in. Two flavors we have are negatively charged an ions and are positively charged. Cat ions and ions air easier for plants. They're dissolved in water in the soil, and that makes them readily available for absorption. Unfortunately, irons dissolved in water are also easily leached from the soil. Leaching is the loss of nutrients through the movement of water. Now there's one exception to all of this. And that is phosphate, which is an an I am. It's p 03 I'm sorry, p 04 three minus very negatively charged and ion. But this is not dissolved in water and soil. It actually forms complexes with calcium and iron cat ions don't need to worry about that too much. Just wanted to point out that not every single anti and is gonna be dissolved in water. Now, cat irons, though they do dissolve in water in soil usually interact with clay and ions or organic acids. And these remember are going to come from humus thes, uh, because these, uh, our cat ions rather interact with clay and humus. It makes them harder for plants to extract. And here, in our example, you can see we have a clay particle with all of these cat ions interacting with it. That's because this clay particle has lots of negative charges. But this could also be a particle of humus, because it, uh, humans has all those organic acids which once they d protein, eight are of course, going to have a negative charge, which is why these cat ions air also going to interact with those organic acids. Now, plants do have a way of getting those cat ions from the soil. We call this cat ion exchange right. You don't get something for nothing. You got to give a little get a little. So basically the way it works is soluble cat ions like protons, and that's what plants they're gonna use. Though cat ion exchange can occur with other cat ions, these soluble cat ions are going to bind to the negatively charged soil particles and cause cat ions like magnesium and calcium, the ions that are nutrients, that the plants want to be released and allow the plants to absorb them. So basically what we're doing or what plants are doing is exchanging one cat iron for another. Remember earlier we said that plant roots will secrete protons, right? Secrete lots of protons. Well, that is to help with caddy. In exchange, it should be noted that humus has what's known as a higher cat ion exchange capacity than does clay. Basically, that means humus will more readily exchange it's cat ions than will a clay particle. Now, plants influence cat ion exchange by releasing Co two as well. And you might remember that CO two is a byproduct of cellular respiration. Right, So the plant roots carry out selling respiration. They're gonna release their CO two, and that CO two is gonna form carbonic acid in water that is found in the soil. So this is going to lead to the release of protons and help facilitate cata and exchange. And you can see that happening in this image here, the plant root is going to release that CO two, which is gonna turn into carbonic acid here. As you can see, it will deep protein ate here. Those protons and then those protons are going to trade places on this negatively charged soil particle with a cat ion. In this case, we have two protons. That's two plus charges so we can take one calcium away. So important to note there that it's not a direct exchange of particles, right? You don't just trade one proton for one magnesium, right? You have to balance charges. So it takes two protons to you protons, for example, to trade with the magnesium. Now it should be noted that if soil gets too acidic, the rain can wash away cat ions, right? Those congee leached from the soil just like the and ions, though it won't happen, is readily unless the soil is very acidic. With that, let's turn the page.

nutrients like ions can easily pass through the cell wall, but the plasma membrane acts like a filter. Remember that term? We talked about selective permeability. The plasma membrane gets to decide what gets in and what doesn't. Plants use proton pumps to create electrochemical Grady INTs, and these Grady INTs allow ions toe enter through transporters. Thes electrical electrochemical radiance are actually strong enough in some cases to overpower counter acting forces like Ph. Radiance. Due to these electrochemical radiance, cat ions like potassium can move through channels. Remember, that's a type of facilitated diffusion. Basically, you just need the channel there, and those ions will move through of their own accord. However, an ions like you know, three here have to use co transporters, and those will often use a proton radiant. And they'll bring a proton into the cell as they bring in the Anna the desired an ion. And remember that this is a form of secondary active transport. Now I an exclusion is this idea that plants are able to filter harmful ions and poisonous metals and prevent them from getting into the cells. They could do this in two ways. What's called passive exclusion and active exclusion. Passive exclusion basically doesn't require any sort of extra energy input. Basically, if the membrane lacks the necessary transporter to allow the ion to pass, it's not getting in. And you might also recall that the cast Berrien Strip is going to force ions into those endo dermal cells because it's going to prevent them from moving all the way through the A pope last to the asylum. So it's gonna force ions to cross a membrane, which gets to act as a filter. So basically here, these transporters, they're kind of like bouncers right there, bouncers. And they get to decide who gets into club cell and who doesn't. Now, active exclusion comes in the form of anti porters. In fact, usually we see these anti porters at the tone of plast, which is the membrane of the HVAC. You'll in our diagram. Here you can see we have evac you'll. This large purple structure inside the plant cell and the tone up last is going to be that membrane of the vacuole. There. Now, a great example of active exclusion is the sodium proton, anti porters or sodium hydrogen ion, anti porters. Whatever you wanna call it, and these were gonna help prevent sodium from poisoning plant cells. Plant cells are actually very sensitive to sodium. They have toe carefully monitor their sodium concentrations, and if the sodium gets too high, they'll actually pull it into the evac you'll to get it out of the way to prevent it from poisoning the plant. The way they do this is they actually use proton pumps to create a proton Grady int so that the concentration of protons inside the vacuole is higher than the concentration of protons just in the cell or in the cytoplasm. This Grady in is going to be taken advantage of by these anti porters. Thes anti porters will move a sodium in as they get rid of one of those protons. So they're going to take advantage of the proton radiant established by the pumps in order to get sodium into the vacuole. So this is a type of secondary active transport, and it involves anti porters at the tone up last. Now, plants also can help prevent poisoning through what are known as metallic thigh ning's. These air Sistine rich proteins that will actually bind uh, two medals and prevent them from poisoning the organism and these air not unique to plants, either. You'll see metallic linings and bacteria and fungi as well, and that's actually all I have for this lesson, so I'll see you guys next time.