Would it surprise you to learn that plants are no different? They also need nutrients to help them survive and thrive in their environments! With that being said, let's explore the world of plant nutrition!
- First, we will talk about soil nutrition.
- Then, we will explore the different micronutrients for plants.
- After, we will look at plant photosynthesis.
- Then, we will talk about the impact of plant nutrition on growth.
- Lastly, we will look at nutrient deficiency in plants.
Soil plant nutrition
For starters, let's talk about how most terrestrial plants obtain nutrients. And, if you guessed that these nutrients come from the soil, you guessed right! The majority of terrestrial plants obtain their nutrients and water from the soil by using their root systems.
To better understand this, let's review the organ system of vascular plants.
Vascular plants are those that have tube-like structures that carry and distribute nutrients.
These plants have two organ systems: the shoot system and the root system.
The shoot system comprises leaves, stems, flowers, and fruits.
A plant's root system anchors the plant and absorbs water and nutrients.
Vascular plants have a vascular system made up of a collection of tissues whose job is to bring water and minerals up from the roots and distribute sugar from the leaves. The vascular tissue is made up of the xylem and phloem.
The xylem tissue transports minerals and water up from the roots, and also provides mechanical support.
The phloem tissue transports the products of organic materials such as sugars around the plant.
Plants have other important structures such as stems, leaves, and roots. The stems provide support to the plant and deliver nutrients from the soil to the leaves. It also brings sugars (ex. glucose) from the plant leaves to its roots. The leaves are the organs of the plants responsible for capturing sunlight for photosynthesis.
The roots are structures that collect nutrients and water from the soil. It also helps plants stay in the plant without being blown or washed away.
Now, let's get into plant nutrition and nutrient transport. Remember that the transport of nutrients in plants is closely coupled to water transport. In other words, one cannot occur without the other!
First, water from the soil (containing dissolved minerals) enters the roots via osmosis.
Then, water travels to the xylem tissue. Water molecules are able to climb the xylem tissue, traveling through the plant, and eventually evaporating from the leaf surface. This process in called transpiration.
Nutrients move from the source cell (where they are made, for example leaf cells that make sucrose) to the sink cell (where they are needed). They are transported through plants in the sieve tubes of the phloem tissue.
How does this happen? Let's take a look!
Companion cells are believed to actively pump nutrients into the sieve tubes, followed by water (water enters the sieve tubes via osmosis). Then, pressure builds up and the nutrient solution moves to the sink. Sugars are unloaded at the sink cell. Then, water leaves the sink cell and travels back to the xylem.
Autotrophic vs. heterotrophic nutrition in plants
Plant nutrition can be classified into two categories: autotrophic and heterotrophic nutrition.
- Autotrophic plants are those plants that are able to make their own food from simple inorganic raw materials.
For example, green plants that exhibit autotrophic nutrition and are able to undergo photosynthesis are called photoautotrophs.
- Heterotrophic plants are not able to synthesize their own organic nutrients from inorganic sources. Instead, they depend on external sources for food.
Heterotrophic plants are further divided into saprophytes, parasitic plants, and insectivorous plants.
Micronutrients for plants
Soil contains different types of nutrients that are essential for plant health. These plant nutrients can be either macronutrients or micronutrients.
A nutrient is an essential element that a plant needs to obtain in order to complete its life cycle (growth and reproduction).
Macronutrients, as the name suggests, are those elements that plants require in relatively large amounts. There are nine macronutrients that you should be familiar with: carbon, oxygen, hydrogen, nitrogen, potassium, calcium, magnesium, phosphorus, and sulfur.
Carbon (C) and Oxygen (O) are taken up from the atmosphere as carbon dioxide (CO2) gas and oxygen (O2) gas and absorbed through leaves.
Hydrogen (H) can come from water (H2O) taken up by roots, or as hydrogen ions (H+) in the soil.
Nitrogen (N) is found in the soil as nitrate (NO3-) and ammonium (NH4+).
Potassium (K) is taken up by roots as potassium ions (K+).
Calcium (Ca) is taken up by roots as calcium ions (Ca2+).
Magnesium (Mg) is taken up by roots as magnesium ions (Mg2+).
Phosphorus (P) is found in the soil mostly as hydrogen phosphate (H2PO4-).
Sulfur (S) is found and taken up by roots are sulfate ions (SO42-).
Micronutrients, on the other hand, are those elements that are only required in small amounts by plants. These are molybdenum, iron, manganese, boron, zinc, copper, chlorine, nickel, and sodium.
Molybdenum (Mo) is taken up by roots as molybdenate (MoO42-).
Iron (Fe) is found in the soil and take up by roots as Ferrous ions (Fe2+).
Manganese (Mn) is taken up by the roots as manganese ions (Mn2+).
Zinc (Zn) is taken up by the roots as zinc ions (Zn2+).
Copper (Cu) is taken up by the roots as cupric ions (Cu2+).
Plant nutrition photosynthesis
Plants are able to perform photosynthesis, and this process occurs in the chloroplasts of leaves. Chloroplasts are photosynthetic organelles found in plants. Inside chloroplasts, we can find chlorophyll, a green pigment responsible for capturing light energy for photosynthesis.
Photosynthesis is the process of converting light/solar energy into chemical energy. The net equation for photosynthesis is: $$ 6\text{ }CO_{2}\text{} + 6\text{ }H_{2}O\text{ }+ \text{Energy } \to 6\text{ }O_{2}\text{ }+ C_{6}H_{12}O_{6} $$
Apart from needing carbon dioxide (CO2), water (H2O), and sunlight for the synthesis of food (sugars) during photosynthesis to occur, nutrients such as nitrogen, sulfate, phosphate, magnesium, iron, and potassium are required for a successful photosynthesis.
Impact of plant nutrition on growth
Nutrient availability plays an important role in plant growth and health. Every plant has a different sufficiency range, and if nutrient levels are not within this range, that plant will have a decline in growth and health.
A plant's sufficiency range is referred to as the range of nutrients necessary to meet that plant's nutritional needs and maximize growth.
If a plant does not get sufficient amounts of a specific nutrient, it will develop a deficiency. Now, if a nutrient is found in excess, toxicity will happen, and plant growth will also decrease.
Nutrient deficiency in plants
When a plant experiences a shortage of certain nutrients due to poor soil quality, for example, then it will suffer from nutrient deficiency. The most common nutrient deficiencies that affect plants are nitrogen, phosphorus, and potassium deficiency.
If a plant has nitrogen deficiency, symptoms include the general yellowing of older leaves, while the rest of the plant looks light green. To prevent or overcome nitrogen deficiency, we can use fertilizers that contain ammonium, nitrate, or urea.
In the case of a phosphorus deficiency, the leaf tips look burnt, whereas the older leaves become reddish-purple or dark green. In this case, fertilizers containing phosphate or "bone" would help.
Now, if a plant suffers from potassium deficiency, the older leaves may wilt and look scorched. To prevent K deficiency, use fertilizers containing sulfates.
Plant Nutrition - Key takeaways
- The majority of terrestrial plants obtain their nutrients and water from the soil by using their root systems.
- Plant nutrition can be classified into two categories: autotrophic and heterotrophic nutrition.
- A plant's sufficiency range is referred to as the range of nutrient necessary to meet that plant's nutritional needs and maximize growth.
- When a plant experiences a shortage of certain nutrients, then it will suffer from nutrient deficiency.
- Macronutrients are elements that plants require in relatively large amounts.
References
- Campbell, N. A., Biology, Pearson, 2017.
- Relyea, R., & Ricklefs, R. E., Ecology : the economy of nature. Macmillan Education, 2018.
- Princeton Review, Fast track biology : essential review for AP, honors, and other advanced study, The Princeton Review, 2020.
- Princeton Review, AP Biology Premium Prep 2021, The Princeton Review, 2020.
- Brown, M., Everything you need to ace biology in one big fat notebook : the complete high school study guide, Workman Publishing Co., Inc., 2021.
- Mccauley, A., Nutrient Management a self-study course from the MSU Extension Service Continuing Education Series Plant Nutrient Functions and Deficiency and Toxicity Symptoms, 2009.
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