PLANT SCIENCE

The Hidden Life of Plants

Plants are complex living organisms that continuously interact with their physical and biological environment. Although a plant may appear relatively static, its tissues are involved in constant processes of water movement, gas exchange, photosynthesis, respiration, nutrient uptake, growth, signalling and interaction with microorganisms.

Understanding plant science provides an important foundation for horticulture. The successful cultivation of plants depends not only on providing suitable light, water and nutrients, but also on understanding how plants function as integrated biological systems. Roots, stems and leaves are closely connected, while plants themselves form part of wider soil and ecosystem processes.

1. Photosynthesis

Photosynthesis is one of the fundamental processes supporting life on Earth. Green plants use light energy to convert carbon dioxide and water into organic compounds, principally carbohydrates, while releasing oxygen as a by-product.

A simplified representation of photosynthesis is:

carbon dioxide + water + light energy → glucose + oxygen

Photosynthesis occurs primarily in the leaves, within specialised organelles called chloroplasts. Chloroplasts contain chlorophyll and other pigments that absorb particular wavelengths of light.

The carbohydrates produced through photosynthesis are fundamental to plant growth and metabolism. Glucose and other photosynthetic products may be used in respiration, converted into starch for storage, incorporated into structural compounds such as cellulose, or transported to other parts of the plant.

Carbon obtained from atmospheric carbon dioxide accounts for a substantial proportion of the dry mass of plants. This means that much of the physical material making up a plant ultimately originates from carbon dioxide in the atmosphere rather than from minerals absorbed from the soil (OpenStax, 2018).

Photosynthesis is influenced by several environmental factors. Light intensity, carbon dioxide concentration and water availability can all affect the rate at which carbon is assimilated. Temperature also affects photosynthetic processes because the biochemical reactions involved depend upon enzyme activity.

Consequently, photosynthesis cannot be considered independently from the rest of plant physiology. A plant requires an appropriate balance of environmental conditions for efficient carbon assimilation and growth.

2. Respiration and the Use of Stored Energy

Photosynthesis stores energy within organic compounds, whereas respiration makes chemical energy available for cellular processes.

Plants respire continuously, both during daylight and darkness. During respiration, organic compounds such as sugars are broken down through biochemical pathways, releasing energy that can be used by cells.

Energy derived from respiration supports processes including:

• cell division;
• tissue growth;
• active transport;
• nutrient uptake;
• synthesis of proteins and other compounds;
• repair of damaged tissues;
• maintenance of cellular structures; and
• development of roots, shoots, flowers and reproductive structures.

Photosynthesis and respiration should therefore be regarded as complementary rather than opposing processes. Photosynthesis captures and stores energy in organic compounds, while respiration releases some of that stored energy for use by the plant.

3. Transpiration and the Movement of Water

Water is essential for plant life. It contributes to cell structure, photosynthesis, metabolic reactions, nutrient transport and the maintenance of plant tissues.

Plants absorb water primarily through their roots and transport it towards the shoots through the xylem. Water movement is closely associated with transpiration, the loss of water vapour from plant surfaces, particularly through stomata in the leaves (OpenStax, 2018).

The majority of transpiration occurs through microscopic pores called stomata. These pores allow carbon dioxide to enter the leaf for photosynthesis, but their opening also provides a route through which water vapour can escape.

This creates a physiological compromise. Plants require open stomata for effective carbon dioxide uptake, but excessive stomatal opening can increase water loss.

Stomata are therefore regulated in response to environmental and physiological conditions.

The transpiration stream

Water moves through the plant in a continuous pathway from the soil to the roots, through the xylem and towards the leaves. Evaporation from internal leaf surfaces creates tension within the water column. The cohesion of water molecules and their adhesion to the walls of xylem tissues contribute to the movement of water through the plant (OpenStax, 2018).

This process can allow water to reach considerable heights in trees without the plant possessing a mechanical pump equivalent to an animal heart.

Transpiration also contributes to the movement of dissolved mineral nutrients from the root system towards the shoots.

The movement of water through the plant is therefore closely linked to:

soil water → roots → xylem → leaves → stomata → atmosphere

This represents one of the most important transport systems in terrestrial plants.

4. The Structure and Function of Roots

Roots perform several interconnected functions.

Their major roles include:

• anchoring the plant;
• absorbing water;
• absorbing mineral nutrients;
• storing carbohydrates;
• conducting water and dissolved substances;
• interacting with microorganisms;
• exploring the soil environment; and
• influencing the physical and chemical properties of the surrounding soil.

Root systems vary considerably between plant species.

Some plants develop prominent taproots, while others produce extensive fibrous or adventitious root systems. Root architecture is influenced by genetic characteristics as well as environmental conditions such as soil structure, water availability, nutrient distribution, compaction and interactions with other organisms.

A root is not simply an underground support structure. It is a dynamic organ capable of responding to changes in its environment.

5. Root Hairs and Absorption

Many young roots develop microscopic root hairs. These structures considerably increase the surface area of the root in contact with the soil.

Water enters root cells through processes associated with differences in water potential. Mineral nutrients may enter roots through both passive and active processes, depending on the nutrient and environmental conditions.

The root system therefore provides an interface between the plant and the soil environment.

This interface is particularly important because soil is not simply a reservoir of mineral nutrients. It contains water, air, organic matter, microorganisms and complex chemical interactions that influence nutrient availability.

Roots continually interact with this environment.

6. The Rhizosphere

The rhizosphere is the region of soil directly influenced by living roots.

Root activity can alter the chemical and biological conditions of this zone. Roots release a variety of compounds, commonly referred to as root exudates, into the surrounding soil.

These compounds can include:

• sugars;
• amino acids;
• organic acids;
• secondary metabolites; and
• other carbon-containing compounds.

Root exudates can influence microbial communities and contribute to interactions between plants and soil organisms.

Consequently, the root should not be viewed as an isolated structure extracting nutrients from an otherwise passive soil. The root is part of a biologically active interface between plant and soil.

Recent research increasingly emphasises the interconnected nature of plants, fungi and bacteria within this environment (Duan et al., 2024).

7. Plants and Soil

Plants influence the development and functioning of soils in several ways.

Living roots can physically penetrate soil and create channels. As roots grow, die and decompose, they contribute organic material to the soil.

Leaves, stems and roots eventually enter decomposition processes, contributing to the formation and cycling of soil organic matter.

Vegetation can also reduce soil erosion.

Plant canopies intercept rainfall before it reaches the soil surface, while stems and leaf litter can slow surface water movement. Root systems help stabilise soil particles and can contribute to the formation of channels and pores within the soil.

These processes demonstrate that the relationship between plants and soil is reciprocal.

The soil provides plants with water, nutrients, physical support and a habitat for microorganisms, while plants influence soil structure, organic matter, nutrient cycling and biological activity.

8. Plants and Soil Microorganisms

Soil contains an enormous diversity of microorganisms, including bacteria and fungi.

Many of these organisms participate in decomposition and nutrient cycling. Organic material is broken down by decomposers, releasing nutrients that can subsequently become available to plants and other organisms.

Plants can also establish specific relationships with microorganisms.

Two particularly important examples are relationships with nitrogen-fixing bacteria and mycorrhizal fungi.

These associations demonstrate that plant nutrition cannot always be understood simply in terms of a plant taking nutrients directly from soil solution.

9. Mycorrhizal Associations

A mycorrhiza is a symbiotic association between a plant root and a fungus.

Mycorrhizal fungi extend through the soil using microscopic filaments called hyphae. These can explore areas of soil beyond the immediate surface of the root.

In many mycorrhizal associations, the plant supplies the fungus with carbon compounds derived from photosynthesis. In return, the fungus can contribute to the plant’s acquisition of mineral nutrients, including phosphorus, as well as influencing water relations and other aspects of plant performance (Genre et al., 2020).

Mycorrhizal associations are extremely widespread among terrestrial plants and represent important biological interactions between plants and fungi.

However, the relationship should not be oversimplified as an automatic exchange in which fungi simply deliver nutrients in return for sugars. The exchange is influenced by the plant species, fungal species, environmental conditions and availability of resources (Walder and van der Heijden, 2015).

The relationship is therefore better understood as a complex biological symbiosis.

10. Plants and the Movement of Carbon

Photosynthesis provides a mechanism through which atmospheric carbon dioxide enters biological systems.

Some of the carbon fixed through photosynthesis remains within leaves and stems. Some is transported to roots, stored as carbohydrates or incorporated into new tissues.

A proportion can also enter the soil through root exudates and interactions with microorganisms and mycorrhizal fungi.

This creates pathways through which carbon moves between the atmosphere, plants, soil organisms and soil organic matter.

The simplified pathway can be represented as:

atmospheric CO₂ → photosynthesis → plant carbohydrates → roots and shoots → soil organisms and organic matter

This is one component of the wider global carbon cycle.

11. Plant Communication and Signalling

Plants do not possess brains or nervous systems comparable with those of animals. Nevertheless, they possess sophisticated systems for detecting and responding to environmental information.

Plants can respond to:

• light;
• gravity;
• temperature;
• water availability;
• touch;
• mechanical damage;
• herbivory;
• pathogens;
• chemical compounds; and
• signals associated with beneficial microorganisms.

Plant signalling involves chemical, electrical and physiological processes.

For example, damage caused by herbivores can activate defensive responses within a plant. Chemical compounds released into the atmosphere can also influence interactions between plants and other organisms.

This is sometimes described as plants “communicating”.

The term can be useful if it refers to the transmission and detection of biological signals. However, it should not be interpreted as evidence that plants communicate through conscious conversations.

Plant signalling is a physiological process involving receptors, chemical messengers, electrical activity and changes in gene expression.

12. Can Plants Share Resources?

Research has demonstrated that resources can move between plants under some circumstances, including through connections involving mycorrhizal fungi.

Early experiments demonstrated the possibility of carbon transfer between plants connected by mycorrhizal fungal networks (Francis and Read, 1984).

However, popular descriptions of forests as being connected by a universal underground “wood wide web” can exaggerate what the scientific evidence demonstrates.

Research has shown that common mycorrhizal networks occur and that resource transfer is possible. However, the frequency, direction, ecological significance and consequences of such transfers vary considerably. Some researchers have argued that evidence is currently insufficient to support broad claims that mature trees routinely send resources or defence signals preferentially to their offspring through such networks (Karst et al., 2023).

The scientifically useful conclusion is therefore more cautious:

Plants can interact through networks involving roots and fungi, and resources can sometimes move through these systems, but the ecological significance of these exchanges depends on the organisms and environmental conditions involved.

This distinction is important because horticulture should be informed by evidence rather than attractive but oversimplified stories.

13. Plants Cooperate and Compete

Plant relationships are not exclusively cooperative.

Plants compete for resources including:

• light;
• water;
• mineral nutrients;
• physical space; and
• reproductive opportunities.

At the same time, plants can form mutually beneficial associations with fungi, bacteria and other organisms.

This means that plant communities are shaped by a combination of:

competition, cooperation, facilitation, predation, parasitism and symbiosis.

A woodland, grassland or garden is therefore a network of interacting organisms rather than a collection of independent plants.

14. The Plant as an Integrated System

The traditional division of plants into roots, stems and leaves is useful for learning their structure, but these organs cannot be understood completely in isolation.

The plant operates as an integrated system.

Roots absorb water and nutrients.

Xylem transports water and mineral nutrients towards the shoots.

Leaves capture light and exchange gases.

Photosynthesis produces carbohydrates.

Phloem transports organic compounds between sources and sinks within the plant.

Roots receive photosynthetic products and use them to support growth and metabolism.

Signals can move between different parts of the plant, coordinating responses to environmental changes.

The plant therefore depends upon continuous communication between its tissues.

15. Water, Carbon and Nutrients: Three Connected Cycles

Plant physiology can be understood partly through three major movements:

Water

soil → roots → xylem → leaves → atmosphere

Carbon

atmosphere → leaves → photosynthesis → plant tissues → soil organisms and atmosphere

Mineral nutrients

soil → roots → plant tissues → decomposition → soil

These cycles are interconnected.

Water is required for photosynthesis.

Photosynthesis produces organic compounds.

Organic compounds support plant growth and interactions with microorganisms.

Plant residues eventually contribute to nutrient cycling.

The movement of water, carbon and nutrients therefore links individual plants to the wider ecosystem.

16. Why Plant Science Matters to Horticulture

Plant science is not simply theoretical knowledge. It has direct applications to practical horticulture.

Understanding roots helps horticulturists make decisions about:

• planting depth;
• soil preparation;
• drainage;
• irrigation;
• compaction;
• transplanting;
• root competition; and
• container cultivation.

Understanding photosynthesis helps explain the importance of:

• light intensity;
• shading;
• leaf area;
• plant spacing;
• temperature;
• carbon dioxide availability; and
• plant health.

Understanding transpiration helps explain:

• water requirements;
• drought stress;
• heat stress;
• humidity;
• ventilation;
• stomatal behaviour; and
• irrigation management.

Understanding soil biology helps horticulturists consider:

• organic matter;
• soil structure;
• microbial activity;
• nutrient cycling;
• root–fungus relationships; and
• the consequences of excessive soil disturbance.

The practical horticulturist therefore benefits from understanding not just what plants need, but why they need it.

17. The Plant as Part of an Ecosystem

A plant is not an isolated organism.

It exists within a complex system involving:

• atmosphere;
• sunlight;
• water;
• soil;
• microorganisms;
• fungi;
• insects;
• herbivores;
• other plants; and
• decomposers.

Through photosynthesis, plants connect atmospheric carbon dioxide with biological systems.

Through transpiration, they influence water movement between soil and atmosphere.

Through roots, they interact with soil structure and microorganisms.

Through decomposition, their remains return organic matter and nutrients to the soil.

Through relationships with fungi and bacteria, they participate in complex networks of nutrient exchange.

The plant is therefore both a biological organism and an important component of wider ecosystem processes.

Conclusion

Plant science reveals that the apparently static plant is an extraordinarily dynamic organism.

Photosynthesis captures energy from sunlight and converts atmospheric carbon dioxide into organic compounds. Respiration releases energy from these compounds to support cellular activity. Transpiration moves water through the plant and links plant physiology with atmospheric conditions.

Roots do much more than anchor plants. They absorb water and nutrients, explore the soil, release compounds into the rhizosphere and interact with microorganisms. Mycorrhizal fungi can form important symbiotic relationships with plant roots, contributing to nutrient acquisition and influencing plant performance.

Plants also influence the soil itself. Root growth, organic matter production, decomposition and interactions with microorganisms contribute to soil development and nutrient cycling.

Plants are capable of sophisticated signalling and can respond to chemical, electrical and environmental information. Resources can sometimes move between plants through biological networks, including mycorrhizal associations, although the ecological importance of these processes is more complex than popular descriptions often suggest.

Understanding these processes changes the way plants can be viewed.

A plant is not simply an object placed into soil.

It is a living system continuously exchanging water, gases, carbon, nutrients and biological information with its environment.

Understanding that system is fundamental to understanding horticulture.

References

Duan, S., Feng, G., Limpens, E., Bonfante, P., Xie, X., Zhang, L. et al. (2024) ‘Cross-kingdom nutrient exchange in the plant–arbuscular mycorrhizal fungus–bacterium continuum’, Nature Reviews Microbiology, 22, pp. 773–790. doi:10.1038/s41579-024-01073-7.

Francis, R. and Read, D.J. (1984) ‘Direct transfer of carbon between plants connected by vesicular–arbuscular mycorrhizal mycelium’, Nature, 307, pp. 53–56. doi:10.1038/307053a0.

Genre, A., Lanfranco, L., Perotto, S. and Bonfante, P. (2020) ‘Unique and common traits in mycorrhizal symbioses’, Nature Reviews Microbiology, 18, pp. 649–660. doi:10.1038/s41579-020-0402-3.

Karst, J., Jones, M.D. and Hoeksema, J.D. (2023) ‘Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests’, Nature Ecology & Evolution, 7, pp. 501–511. doi:10.1038/s41559-023-01986-1.

OpenStax (2018) Biology 2e. Houston, TX: OpenStax, Rice University. Available at: OpenStax Biology 2e (Accessed: 27 September 2026).

Oldroyd, G.E.D. (2013) ‘Speak, friend, and enter: signalling systems that promote beneficial symbiotic associations in plants’, Nature Reviews Microbiology, 11, pp. 252–263. doi:10.1038/nrmicro2990.

Walder, F. and van der Heijden, M.G.A. (2015) ‘Regulation of resource exchange in the arbuscular mycorrhizal symbiosis’, Nature Plants, 1, article 15159. doi:10.1038/nplants.2015.159.