Function of Nutrients in Plants

Notes for RHS Level 2: Unit 1: Element 2 Role of Nutrients: AO1: Function of Nutrients in Plants

The essential nutrients required for plant growth and development are divided into two categories: macronutrients and micronutrients.

Macronutrients are elements that plants require in larger amounts, with the elements used in the highest quantities gained from the air, being carbon, hydrogen, and oxygen. Erosion slowly releases all the other minerals from the Earth’s rocks.

Whether minerals are obtained from organic sources, such as composted vegetable matter, or inorganic sources, such as liquid blends of chemicals, does not matter to the plant as the mineral elements are the same.

However, the main difference is that organic sources slowly release small quantities of minerals into the soil, whereas inorganic fertilisers use concentrations of specific elements prepared for defined and immediate usage.

N-P-K ratios on fertiliser display the ratios between nitrogen, phosphorus, and potassium (K refers to the now obsolete neo-latin kalium). For example a formulation using a ratio of 0-10-10 would promote flower and fruit set.

The following table lists the macronutrients and their functions in plants:

 

Nutrient               Function

Nitrogen             Essential for the production of chlorophyll, amino acids, and nucleic acids.

Phosphorus        Involved in the production of ATP, DNA, and cell membranes.

Potassium           Regulates water balance, activates enzymes, and helps in the production of ATP.

Calcium              Essential for cell wall formation, cell division, and cell elongation.

Magnesium         A component of chlorophyll, and is involved in photosynthesis and enzyme activation.

Sulfur                  Required for the production of amino acids, proteins, and enzymes.

Carbon                Required for photosynthesis, the process by which plants produce their own food.

Oxygen               Required for respiration, the process by which plants convert food into energy.

Hydrogen            Required for the formation of organic compounds, such as carbohydrates and proteins.

 

In addition to macronutrients, plants also require micronutrients in smaller amounts for their growth and development. The following table lists some of the essential micronutrients and their functions in plants:

 

Nutrient               Function

Iron                    Essential for the production of chlorophyll and involved in photosynthesis.

Boron                 Required for cell wall formation, pollen tube growth, and seed production.

Manganese         Involved in photosynthesis, respiration, and enzyme activation.

Molybdenum      Required for nitrogen fixation and the production of enzymes.

 

Plants lacking macronutrients and micronutrients will find their growth and development adversely affected, leading to mineral nutrient deficiencies and disorders. The symptoms of nutrient deficiency can vary depending on the nutrient that is lacking. For example:

Nitrogen deficiency:        Plants may exhibit stunted growth, yellowing of leaves, and reduced leaf size.

Phosphorus deficiency:   Plants may exhibit stunted growth, dark green leaves, and reduced root growth.

Potassium deficiency:     Plants may exhibit yellowing of leaf margins, wilting, and reduced growth.

 

Deficiencies will be explored further in a future post.

Impact on plant specification on biosecurity (UK)

 Notes for Unit 1: Plant Specification: Integration: AO3 Impact on specification on biosecurity

 

Plant specification has a significant impact on biosecurity. When ordering plant material, it is important to consider the biosecurity of the plants you order. You should only order plant material from reputable suppliers who follow strict biosecurity protocols.

There are also strict rules for the importation of plants into the UK from the EU, including the necessity for a phytosanitary certificate. This certificate is issued from the plant health authority of the country where the plant material originates to guarantee that the material has been officially inspected, is free from pests and diseases and meets the legal requirements for the material to enter GB. There are costs associated with the importation process related to applying for phytosanitary certificates, checks and inspections that an individual importer is expected to meet. This does not apply to all plants, as there is a short list of low-risk plants that can be imported from the EU and third countries without the phytosanitary certificate. At the time of writing, this includes, but is not limited to, pineapple, persimmon, and banana. See the links below for further information.

 

UK Plant Passport

In addition, the UK has introduced a plant passport scheme and plants cannot use an EU plant passport for movement in the UK. While garden centres do not need to pass on a UK plant passport to customers, online retailers must supply the passport for traceability purposes.

 

The plant types you choose can also have an impact on biosecurity. Different plant types have different susceptibility to pests and diseases. For example, some plant types such as annuals and biennials are more susceptible to pests and diseases than others such as perennials. Schemes such as the RHS Award of Garden Merit have a series of requirements that ensure plants awarded are reasonably resistant to pests and diseases.

 

Material type is another important factor to consider when ordering plant material. The three main types of plant material are pot-grown, bare root, and rootballed / burlap. Each material type has its own advantages and disadvantages in terms of biosecurity. For example, bare root and pot grown plants are financially cheaper, but are more susceptible to damage during transportation, which can increase the risk of pest and disease transmission. While, the well developed root systems of rootballed/burlap plants, which are available during the dormant season for the species, are less susceptible to damage and therefore less likely to be infected with disease.

Bare root, rootballed, and potted plants.

 

Production method is also an important consideration. Plants can be grown using different methods such as conventional, organic, or biodynamic. It is important to choose a production method that aligns with your values and requirements.

Conventional production methods use synthetic fertilizers and pesticides to promote plant growth and control pests and diseases. While these methods are effective, they can have negative impacts on the environment and human health.

 

Organic production methods use natural fertilizers and pest control methods to promote plant growth and control pests and diseases. Organic methods are more sustainable and environmentally friendly than conventional methods, but they can be more expensive and less effective. For instance, the reliance on natural predators to remove pests can be less effective, while using natural compost and manure can introduce soil-borne diseases.

 

Biodynamic production methods are similar to organic methods, but they also incorporate spiritual and mystical practices. Biodynamic methods are less common than conventional and organic methods, but they are gaining popularity due to their focus on sustainability and holistic plant health. However, as with organic production, the reliance on natural predators to remove pests can be less effective, while using natural compost and manure can introduce soil-borne diseases.

 

Finally, environmental considerations are also important when ordering plant material. You should choose plants that are well-suited to your local climate and soil conditions. You should also consider the environmental impact of the production and transportation of the plant material.

 

By considering these factors, you can ensure that you order plant material that is healthy, sustainable, and well-suited to your needs.

 

Links for further information:
https://www.rhs.org.uk/prevention-protection/importing-and-exporting-plants

https://www.gov.uk/guidance/apply-for-plant-export-certificates-and-inspections

https://aphascience.blog.gov.uk/2023/03/01/plant-passports/

New Plant Biosecurity Strategy - UK Plant Health Information Portal (defra.gov.uk)

 

Plant Lifecycle Adaptations

Personal notes for RHS Level 2 Certificate in the Principles of Plant Growth and Development
Unit 1: Plant Science 1: Lifecycle adaptations: AO2 Application

Plant life cycle adaptations have several advantages that help them survive in different environments. Some of these advantages include:

Exploitation of short growing season: In regions with a short growing season, plants have adapted to grow and reproduce quickly before the onset of winter. This adaptation allows them to complete their life cycle within a short period of time and produce seeds that can survive the winter and germinate in the following spring.

For example: Alpine forget-me-not: This plant is found in the alpine regions of Europe and has adapted to grow and reproduce quickly before the onset of winter.

Avoidance of extreme weather conditions: Plants have evolved various mechanisms to avoid extreme weather conditions such as drought, frost, and heatwaves. For example, some plants have developed deep roots to access water from underground sources, while others have developed thick leaves to reduce water loss through transpiration.

For example: Cushion plants: These plants are compact and low-growing, which helps them survive in cold and windy conditions. They trap airborne dust and use it as a source of nutrients.

Ecological niches: Plants have adapted to occupy specific ecological niches, which are unique habitats that provide specific environmental conditions. For example, some plants have adapted to grow in acidic soils, while others have adapted to grow in saline soils.

For example: xerophytic plants such as Joshua tree which has evolved a deep root system that allows it to access water stored deep in the soil. Its spiky leaves also help to reduce water loss through transpiration.

Growth in less favourable conditions: Plants have adapted to grow in less favourable conditions such as low light, low nutrient availability, and high salinity. For example, some plants have developed mechanisms to capture and digest insects to obtain nutrients, while others have developed symbiotic relationships with fungi to obtain nutrients.

For example, plants known as halophytes have evolved to tolerate high levels of salt in their environment, this includes Hibiscus syriacus, also known as rose of Sharon, this plant is a moderately salt-tolerant shrub that can grow in saline soils but in more extreme environments, Spartina alterniflora, also known as smooth cordgrass, is a plant that is found in salt marshes and can tolerate high levels of salt in the soil.

These adaptations have allowed plants to thrive in different environments and play a crucial role in maintaining the balance of ecosystems.

Agents of natural pollination

Personal notes for RHS Level 2 Certificate in the Principles of Plant Growth and Development

Unit 1: Plant Science 1: Pollination and fertilisation: AO1

The agents of natural pollination are diverse and can be broadly classified into two categories: biotic and abiotic.

𝐁𝐢𝐨𝐭𝐢𝐜 𝐚𝐠𝐞𝐧𝐭𝐬 include pollinating animals such as bees, moths, flies, and birds.

The biotic agents are attracted to a flower due to such features as its colour, shape, or aroma.

The visitor to a flower then becomes a potential agent for pollination transfer, with the pollen from the male reproductive organ, known as the anther, dusted onto the animal's body. Should the animal then visit another flower of the same species, this pollen may then be inadvertently brushed onto the stigma, the female reproductive organ.

Whether pollination successfully leads to fertilisation on the same flower, or a different flower of the same species will depend on the species visited.


Flower shape can be a determining factor as to which species are able to visit the flower. Some flowers have evolved to perfectly match specific animal species. Perhaps, the most well-known example of this is the Star orchid (Angraecum sesquipedale), which is pollinated by the long-tongued moth commonly known as Morgan's predicted Sphinx moth. In 1862, Charles Darwin examined this orchid, predicting (supported by Alfred Russel Wallace) that a long-tongued moth would be found that pollinated it; no moth with that extreme length of tongue was known at the time.

Then, in 1903, he was proven correct when a long-tongued moth, Xanthopan morganii praedicta was discovered. It was so named because its occurrence had been predicted.

𝐀𝐛𝐢𝐨𝐭𝐢𝐜 𝐚𝐠𝐞𝐧𝐭𝐬 include wind and water.

Wind-pollinated plants produce large amounts of pollen that is light in weight and easily carried by the wind. Some examples of wind-pollinated plants in the UK include willow (Salix), alder (Alnus), and birch (Betula)


Water-pollinated plants, on the other hand, release their pollen into the water, where it is carried to the female reproductive organs. Some examples of water-pollinated plants in the UK include water thyme (Hydrilla), ditch grasses (Ruppia), and waterweeds (Elodea).

Photo: Bumblebee (Bombus species) visiting Cowslip (Primula veris).

Basics of Life cycle adaptations

Personal notes for RHS Level 2 Certificate in the Principles of Plant Growth and Development
Unit 1: Plant Science 1: Lifecycle adaptations: AO1

Life cycle adaptations are the ways that plants have evolved to survive and reproduce in different environments. Based on their life cycle, plants can be classified into five categories:

• Ephemeral plants are those that have several life cycles in one growing season. They can germinate, grow, flower, and produce seeds in a short period of time, usually in response to favourable conditions such as rainfall. They can increase in numbers rapidly and colonize disturbed habitats. An example of an ephemeral plant is groundsel (Senecio vulgaris).
• Annual plants are those that complete their life cycle in one year or growing season. They germinate from seeds, grow, flower, produce seeds, and die within a year. They can be hardy, half-hardy, or tender, depending on their ability to withstand frost and low temperatures. Examples of annual plants are zinnia (Zinnia elegans) and marigold (Tagetes patula).
• Biennial plants are those that complete their life cycle in two years or growing seasons. They germinate from seeds and grow vegetatively in the first year, then flower, produce seeds, and die in the second year. Some plants that are botanically perennials are grown as biennials because they perform poorly after flowering. Examples of biennial plants are foxglove (Digitalis purpurea) and wallflower (Erysimum cheiri).
• Perennial plants are those that live for more than two years or growing seasons. They can be herbaceous or woody, depending on the presence or absence of secondary growth in their stems. Herbaceous perennials are non-woody plants that die back to a rootstock each autumn and regrow in the following spring.
  Examples of herbaceous perennials are hop (Humulus lupulus) and peony (Paeonia lactiflora).
  Woody perennials are plants that maintain live woody stems throughout the year and exhibit secondary growth. Examples of woody perennials are lilac (Syringa vulgaris) and oak (Quercus spp.).

Plant Stems (Internal)

Personal notes for RHS Level 2 Certificate in the Principles of Plant Growth and Development

Unit 1: Plant Science 1: Internal Plant Structures: AO1 - AO2

The diagram illustrates a simplified stem followed by a close-up of the different layers.

Working from outer to inner tissues we begin with the epidermis, a protective, single layer, which produces an outer wax layer of cuticle call cutin, which is waterproof. Punctuating the epidermis layer are stomata pores, allowing gases to pass through the otherwise impermeable layer.

Underneath the epidermis is the cortex, largely constructed of unspecialised parenchyma tissue. These thin-walled cells are held in an approximately spherical shape by osmotic pressure, with many air spaces between them. This mass of cells also combines to assist with maintaining the plant shape, in addition to other functions, such as containing chlorophyll and releasing energy via respiration for use by surrounding tissues. In some plants, they can act as food stores, as in potato tubers.

Phloem and Xylem are the two vascular bundles within plant stems:
Phloem, containing long, tube-like cells, is responsible for transporting organic nutrients (such as sugars) from the leaves to other areas of the plant.

Xylem, containing long, wide, and open-ended cells with thick lignified walls, is the dead, permanent tissue located at the centre of the vascular bundle. It transports water and dissolved minerals from the roots to other plant parts.

In dicotyledons resides the vascular cambium, a lateral meristem which contains actively dividing cells that produce more phloem and xylem tissue. This increases the girth of the stem in woody plants and is known as secondary thickening. The bundles are arranged in a ring providing both strength and support.

Pith refers to the central zone of the stem, mainly made up of parenchyma cells. These can break down to leave a hollow stem.

There are two final cells to mention in this section, collenchyma and sclerenchyma:

Collenchyma provides extra mechanical and structural support, especially in regions of new growth. It helps young stems and leaves maintain their shape and withstand bending forces.

Sclerenchyma provides the main structural support to a plant. Unlike collenchyma, mature sclerenchyma cells are generally dead at maturity.

Basic Plant Taxonomy

Personal notes for RHS Level 2 Certificate in the Principles of Plant Growth and Development

Unit 1: Plant Science 1: Scientific and common plant names: AO1.

In horticulture, plant taxonomy is the science of classifying plants based on their characteristics and evolutionary relationships. It involves categorizing plants into different groups based on their physical and genetic traits.

A family is a group of plants that share similar characteristics and are related to each other through a common ancestor. Members of a family share similar flower structures, fruit types, and other physical features.

A genus is a group of plants that share similar characteristics and are closely related to each other. Members of a genus share similar flower structures, fruit types, and other physical features. Examples of genera include Rosa (roses), Ficus (figs), and Acer (maples).

A species is a group of plants that share similar characteristics and can interbreed to produce fertile offspring. Members of a species share similar flower structures, fruit types, and other physical features. Examples of species include Rosa canina (dog rose), Ficus carica (common fig), and Acer saccharum (sugar maple).

A cultivar (cultivated variety) is a variation within a plant species that has been selectively bred by humans for specific desirable traits, such as color, size, or disease resistance. Cultivars are usually propagated asexually (e.g., by cuttings or grafting) to maintain their desirable traits. Examples of cultivars include Rosa ‘Peace’ (a hybrid tea rose), Ficus ‘Brown Turkey’ (a fig cultivar), and Acer ‘October Glory’ (a red maple cultivar).

A variety is a naturally occurring variation within a species that has been selected for specific desirable traits. Varieties can be propagated sexually (e.g., by seed) or asexually (e.g., by cuttings or grafting) to maintain their desirable traits. Examples of varieties include Rosa canina var. glauca (a dog rose variety with blue-green leaves), Ficus carica ‘Black Mission’ (a fig variety with dark purple fruit), and Acer saccharum var. nigrum (a sugar maple variety with dark bark).

A species is a plant that is the result of crossbreeding two different species or cultivars. Hybrids can be created for specific desirable traits, such as disease resistance, hardiness, or color. Examples of hybrids include *Rosa ‘Double Delight’ (a hybrid tea rose), Ficus ‘Janice Seedless’ (a fig hybrid), and Acer x freemanii ‘Autumn Blaze’ (a red maple hybrid)

* seen in photograph (via Wikipedia).