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Leaf Area - How & Why Measuring Leaf Area is Vital to Plant Research

Posted by: Scott Trimble
April 16, 2019

What is Leaf Area?

It is easy to measure leaves, and they are also the parts of a plant most responsive to their environment. The combination of these two factors makes leaf area measurement extremely useful to scientists and growers. Besides, leaves are one of the main plant organs and are responsible for the productivity of a plant, and on a larger scale, of an ecosystem or a farm. Therefore, an understanding of leaf area and the different methods to measure it is important.

Why is Leaf Area Important?

Leaves are one of the most important organs that plants have. Photosynthesis, the process by which plants produce food using light, carbon dioxide (CO2), and water, takes place in leaves. The structure and makeup of leaves are designed for photosynthesis.

  • Light is captured by chloroplasts in leaves.
  • Carbon dioxide is taken in through stomata, or openings on the underside of leaves.

Many other important interactions with the environment also happen through leaves.

Evapotranspiration

Since the internal tissue of plants always has a higher water content than the air, water in the form of water vapor escapes through the stomata when they opens to let in CO2 through a process called transpiration. Plants have to regulate the opening of stomata to achieve a balance between taking in enough CO2 and restricting the loss of water vapor.

Keeping the stomata closed to conserve water, restricts CO2 uptake, resulting in less food production.

If too much water is lost through transpiration, the plant needs to absorb more water from the ground. This happens as a physical reaction to high levels of transpiration that result in negative pressure, which in turn causes the plant to being pulling more water through its roots.

This set of circumstances has significant consequences for plants:

  • In drier regions or in higher canopies, where there is abundant sunlight and relatively high temperatures, plants have smaller leaves.
  • In wetter areas and lower canopy levels with less light or lower temperatures, plants will have larger leaves.

In crop production, excessive transpiration means more irrigation and fertilizer use, as water is the medium through which the plant moves nutrients internally.

It is therefore easy to see how leaf area affects different plant dynamics in both natural ecosystems and food production. Not surprisingly, leaf area is one of the most important leaf traits studied.

Leaf Plasticity

Some plant parts are responsive and react quickly to changes in their environment. Leaves are considered to be the most plastic plant organ. This trait makes leaves ideal indicators for short-term and long-term changes in environmental stimuli, such as:

  • Light
  • Water availability
  • Temperature
  • Nutrient availability
  • Soil Type

leaf area per gram fruit

Figure 1: Average weight of Tokay grapes (g) of at harvest on leaf area per unit crop weight (cm2/g). From Kliewer, W.M. & Dokoozlian N.K. (2005). (Image credits: http://www.ajevonline.org/content/56/2/170)

Disciplines Using Leaf Area Measurements

Leaf area measurement is a reliable parameter in studying the impact of environment on plants in the disciplines of ecology, genetics, and crop management. Ecophysiologists, geneticists, botanists, ecologists, environmental scientists, and agronomists are some of the occupations that use leaf area measurements.

  • Ecology: The effect of deforestation or reforestation on plants in the understory can be studied using leaf area measurements. Leaf area measurements by handheld tools are ideal for field measurements in forests and other natural ecosystems.
  • Adaptation to the environment: Since leaf size is an adaptation and response to the environment, it can be considered an indicator of the conditions plants grow in: climate, topography, soils, etc. These relationships are interesting for geneticists, ecologists, and agronomists.
  • Crop stress: Biological and physical stress such as herbivory, grazing or drought can be tracked through leaf area. Ecophysiologists use leaf area measurements when researching crops or natural ecosystems.
  • Crop optimization: Agricultural practices aim to improve growing conditions for plants. Leaf area is one of the aspects measured by agricultural scientists, especially agronomists, to establish the best agricultural practices. Similarly, farmers can check if they are creating an ideal environment for their annual and perennial crops.

Measuring Leaf Area

There are destructive and non-destructive methods of measuring leaf area. Some of the common methods are discussed below:

Direct measurements: This involves taking the length and width of a leaf and using weighted regression equations for each species to get the leaf area. The equation used is

𝐴 = 𝑏 × 𝑙 × 𝑤

where l is the length, w is the width of the leaf at its widest point, b is the leaf shape coefficient that varies from species to species, and A is the leaf area.

Millimeter graph paper method: Here a leaf is taken and traced over graph paper, and the grids covered by the leaf are counted to give the area. This method can be both inaccurate and time consuming, and it is also impractical when many measurements are necessary.

Planimeter: This is the simplest tool that is used, but it is destructive. A leaf is plucked and its boundary traced. The planimeter measures the dimensions, and the area is calculated.

Image processing: Images of multiple leaves using a taut bounding area are taken from the top, the side, and obliquely. Average values for each view are calculated using leaf region segmentation, region filling, and area calculation. Imaging can be non-destructive and done in many ways.

Digital scanners: Digital scanners and their accompanying software use a pixel counting method to measure leaf area. This method is fast and non-destructive.

It is best to take measurements of leaves around sunrise or sunset when the leaf is under the least stress from light and heat. The leaves chosen for measurements must be from plant parts exposed to sunlight. Measure two randomly selected leaves from each plant. Take measurements from at least ten plants in a field.

CID Bio-Science offers two lightweight instruments for accurate and non-destructive measurements of leaf area in the field: the CI-202 and CI-203.

CI-202 Portable Laser Leaf Area Meter: This is a laser scanner which measures length and width to provide leaf area and perimeter measurements, and it also calculates aspect ratio and shape factor.

  • It has a resolution of 0.01 cm2 and requires no calibration.
  • The accompanying data logger, software, and USB can store up to 8000 readings and transfer it to computers.
  • The CI-202 provides instant results and covers 200mm/second.

CI-203 Handheld Laser Leaf Area Meter: This leaf meter has a laser beam and an optical motion sensor to take the length and width to calculate the leaf area and perimeter. It also measures the shape and aspect ratio of leaves.

  • A built-in GPS allows each leaf to be tagged by its location, making it possible to track the growth of a leaf or plant.
  • A Wi-Fi card and USB make data transfer easy. The CI-203 can store 15,000 data points.
  • Detached leaf measurements are possible in combination with the Conveyor Attachment (CI-203CA).


Additional Reading

To find out more about the fascinating relationship between the environment and leaves and how to measure leaves directly, check out the following articles:

The Increasing Importance of Leaf Area

Leaf area studies and measurements will become more important in the future with temperatures rising due to climate change. Instruments such as leaf area meters allow growers of crops, fruits, vegetables, and flowers to detect changes in the growing environment of plants. Leaf area meters are also vital for studying plant responses to the environment and for optimizing yields in a changing climate.

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Vijayalaxmi Kinhal
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture

Sources

Easlon, H. M., & Bloom, A. J. (2014). Easy Leaf Area: Automated digital image analysis for rapid and accurate measurement of leaf area. Applications in plant sciences, 2(7), apps.1400033. doi:10.3732/apps.1400033

F.J. Montero, F.J., de Juan, J.A., Cuesta, A., & Brasa, A. (2000). Nondestructive Methods to Estimate Leaf Area in Vitis vinifera L. HortScience 35: 696–698. https://doi.org/10.21273/HORTSCI.35.4.696

Kemp, C.D. (1960). Methods of Estimating the Leaf Area of Grasses from Linear Measurements. Annals of Botany, 24:491–499, https://doi.org/10.1093/oxfordjournals.aob.a083723

Kliewer, W.M. & Dokoozlian N.K. (2005). Leaf Area/Crop Weight Ratios of Grapevines: Influence on Fruit Composition and Wine Quality. Am J Enol Vitic. 56: 170-181. Retrieved from http://www.ajevonline.org/content/56/2/170

Kunzmann, D. Retrieved from https://uol.de/fileadmin/user_upload/biologie/ag/landeco/download/ LEDA/Standards/Leda-S3-2_leaf_traits.pdf

Leaf Shapes and Strategies. (2009, July 12). The Virtual Nature Trail at Penn State New Kensington. Retrieved by https://www.psu.edu/dept/nkbiology/naturetrail/leaves.htm

Melo Jr, J.C.F., & Boeger, M.R.T. (2016). Leaf traits and plastic potential of plant species in a light-edaphic gradient from a Restinga in southern Brazil. Acta biol. Colomb.21:51-62. doi: http://dx.doi.org/10.15446/abc.v21n1.47621.

Nyakwende, E., Paull, C. J. & Atherton, J. G. (1997) Non-destructive determination of leaf area in tomato plants using image processing, Journal of Horticultural Science, 72:2, 255-262, DOI: 10.1080/14620316.1997.11515512

Pandey, S.K., & Singh, H. (2011) .A Simple, Cost-Effective Method for Leaf Area Estimation. Journal of Botany, 2011: 6 pages. https://doi.org/10.1155/2011/658240.

The Audiopedia. (2018, July 9) What is Specific Leaf Area? Retrieved from
https://www.youtube.com/watch?reload=9&v=zIRstgKci30

What are leaves and why are they important? (2016, August 18). Retrieved from https://cid-inc.com/use-case/what-are-leaves-and-why-are-they-important/


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Scott Trimble

Marketing Director

strimble@cid-inc.com

1-360-833-8835 ext. 217