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Plant Nutrition

Plant Nutrition

You've probably been told to drink milk because it contains calcium, which plays an essential role in bone health. Or perhaps you have been advised to eat bananas to relieve a muscle cramp because bananas contain potassium, which is an electrolyte that aids muscle function. Whatever you’ve heard, it has a basis in dietary health since we must get certain nutrients to carry out our biological functions.

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.

  • The process of osmosis involves water molecules diffusing across a partially permeable membrane from a high-concentration region to a low-concentration region.

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.

  • Plants that feed on decaying matter are saprophytes. They release enzymes that break down complex organic compounds into simpler forms, which can be absorbed by plants. An example of a saprophytic plant is the Indian pipe plant Monotropa.

  • Parasitic plants are plants that get their nutrition from attaching itself to the host.
  • Insectivorous plants are plants that feed on insects (for example, the Venus flytrap plant).

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.

For a review on chloroplast structure, check out "Mitochondria and Chloroplasts"!

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

  1. Campbell, N. A., Biology, Pearson, 2017.
  2. Relyea, R., & Ricklefs, R. E., Ecology : the economy of nature. Macmillan Education, 2018.
  3. Princeton Review, Fast track biology : essential review for AP, honors, and other advanced study, The Princeton Review, 2020.
  4. Princeton Review, AP Biology Premium Prep 2021, The Princeton Review, 2020.
  5. Brown, M., Everything you need to ace biology in one big fat notebook : the complete high school study guide, Workman Publishing Co., Inc., 2021.
  6. 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.

Frequently Asked Questions about Plant Nutrition

Most plants get the majority of their nutrients from the soil using their root systems. 

Plant nutrition involves all the nutrients necessary for a plant for growth and stay healthy.

Plants gets most nutrients from the soil. If the soils contain too little or too much nutrient, it can lead to either a nutrient deficiency or toxicity. 

The three most common nutrient deficiencies in  plants are nitrogen, phosphorus, and potassium deficiency.  

A plant will only grow successfully if the amount of nutrients available for its growth falls within that plant's sufficiency range. 

Final Plant Nutrition Quiz

Question

What is a sink?

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Answer

A portion of the plant that keeps growing

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Question

What is a source?

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Answer

A source is a part of the plant that creates organic compounds

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Question

Translocation is bi-directional

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Answer

True

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Question

How many specialized cells are there in the phloem?

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Answer

4

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Question

Which are examples of sources?

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Answer

Green leaves

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Which are examples of sinks?

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Answer

Roots

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Question

Phloem is living tissue

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Answer

True

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Question

Which is correct?

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Answer

The symplastic pathway is via cell cytoplasms and the apoplastic pathway is via cell walls

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Question

What are the four specialized cell types? 

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Answer

Sieve tube elements, companion cells, phloem fibers, and parenchyma cells

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How do companion cells help sieve tubes?

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Answer

They provide metabolic support

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What do sieve tubes do? 

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Answer

They transport amino acids and sugars

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What do phloem fibers do?

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Answer

Provide structural support for the plant

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What are parenchyma cells?

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Answer

They are permanent ground tissue 

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Question

ATP is needed to transport assimilates between the sources and sinks

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Answer

True

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Question

What is plasmodesmata? 

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Answer

They are intracellular channels along the plant cell wall and facilitate the exchange of sucrose and signaling molecules between cells

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Question

What are the functions of xylem?

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Answer

It transports water and inorganic ions while also providing support for the plant

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Question

Xylem forms a vascular bundle with phloem 

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Answer

True

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Question

What is a source?

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Answer

It is where the plant creates the food like the leaves

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What is a sink?

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Answer

It is where the food is stored or used like the roots

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Question

Transpiration is unidirectional

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Answer

True

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Question

How many specialized cells are there in xylem?

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Answer

4

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Question

What are tracheids? 

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Answer

Long and narrow hardened cells with pits

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Question

Xylem is completely a living tissue

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Answer

False

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Question

What is the function of parenchyma? 

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Answer

It is the only living tissue in xylem and it stores oils and starches

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Question

What are sclerenchyma? 

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Answer

They are xylem fibers

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Question

What are the two xylem vessel elements?

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Answer

Meta-xylem and proto-xylem 

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Question

What provides mechanical strength for the xylem in the plant?

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Answer

Lignin

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Question

How are xylem and phloem organized in dicots? 

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Answer

Ring-like structures

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How are xylem and phloem organized in monocots? 

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Answer

Scattered

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What are the five differences between monocots and dicots? 

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Answer

The seeds, the roots, the vascular structure of the stem, the leaves, and the flowers

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Question

What process leads to the varying size of soil particles?

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Answer

Weathering of rocks

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What is soil solution?

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The mixture of water and dissolved minerals in the spaces found in the gaps between soil particles

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Question

Describe the water retention of sandy soils.

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Answer

Sandy soils have large spaces between soil particles. As such, it usually does not retain enough water to enable plants to grow vigorously.

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Describe the water retention of clayey soils.

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Answer

Clayey soils have tiny spaces between soil particles. As such, it usually retains too much water causing the roots to suffocate from the lack of oxygen.

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What determines the capacity of soil particles to bind nutrients?

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Answer

Surface charge

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What is leaching?

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Answer

The loss of water-soluble plant nutrients

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What is water percolation?

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Answer

The movement of water through the soil

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Question

Why is loam soil ideal for plant growth?


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Answer

Loam soil is composed of sand, silt, and clay in equal proportions. Loam has small soil particles in the form of silt and clay, creating enough surface area for mineral and water adhesion and retention.

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Question

What type of ions are prone to leaching?

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Answer

Negatively-charged ions are prone to leaching

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Why are soil nutrients important for plant growth?

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Answer

Without nutrients a plant may be unable to complete its life cycle—its seed may not germinate; the plant may not form healthy roots, stems, leaves, or flowers; it may be unable to produce seeds; or the plant itself may die. 

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What makes up the organic matter in soil?

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Answer

Organic components in soil include living organisms like bacteria and fungi, as well as humus, the organic matter produced by decaying animal and plant matter.

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How does soil pH affect nutrient availability?

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A plant’s optimal pH depends on organic matter content and plant type. The pH of the soil influences how securely nutrients are bound to soil particles. Many nutrients become unavailable to the plant when the soil pH is either too high (basic) or too low (acidic) since they can no longer dissolve in soil water.

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Question

Essential plant micronutrients like iron, nickel, and boron are needed in ___ amounts.

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Answer

small

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Question

How does growing crops affect soil nutrients?

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Answer

Growing crops can remove nutrients from soil. For this reason, fertilizers–mineral nutrients added to soil–are used to restore soil fertility, enabling the seasonal cultivation of crops at fixed locations.

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Question

Which of the following essential plant nutrients is usually needed in large amounts?

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Answer

Nitrogen

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Question

What is mineral deficiency?

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Answer

Mineral deficiency occurs when a plant does not have an adequate supply of an essential nutrient necessary for its growth and development. 

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What happens to plants that have mineral deficiency?

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Answer

Plants that lack essential nutrients will not grow effectively and will exhibit a variety of symptoms to indicate deficiency.

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Question

What does mobility of a mineral mean?

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Answer

Mobility is the ability of a nutrient to move within a plant.

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Question

Deficiency in mobile elements manifests in ___ organs first.

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Answer

older

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Question

Deficiency in immobile elements manifests in ___ organs first.

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Answer

younger

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