Studying Oak Response to Light Variability in Forests with a Portable Laser Leaf Area Meter

Leaf area measurements, along with other leaf dimensions, are important parameters to establish morphological plasticity in trees with a broad climatic range. In one such experiment, Iranian scientists decided to use a Leaf Area Meter to get precise data rapidly. This laser-based forestry technology helped scientists understand how trees adapt to light and could have applications in forest management.

Finding Evidence of Physical Plasticity in Oak Response to Light

Leaves are important above-ground organs of trees. They are involved in gaseous exchanges such as photosynthesis, transpiration, and respiration, which decide a plant’s growth and productivity.

Leaves are also sensitive to their environments, including light or availability of soil water and nutrients, and have to adapt in response to these factors in the short-term. They can do this if they have phenotypic plasticity.

Plasticity is defined as the ability of a single genotype to respond differently to varying environments.

Phenotypic plasticity allows a species to produce a range of leaf traits. This feature is important for trees that have a broad environmental niche, such as the common oak (Quercus castaneifolia).   

Light is a vital factor for plant development. Its availability changes in space and time, depending on the presence of an overlying canopy layer, the season, or extreme weather events. Changes in leaves in response to available solar radiation are common.

Regardless of the importance of physical plasticity, trees have been known to show greater physiological plasticity.

Hence, a group of Iranian scientists—Babei, Jalali, Sohrabi, and Shirvany—wanted to see if they could find evidence for physical or morphological plasticity. They tested five populations of oak growing along a moisture and light gradient.

They chose chestnut oaks growing from a mountain range to the coast. They wanted to see if the physical parameters of the oak leaves differed in response to changing light conditions. Also, if these leaf traits would show up in short-term responses to light.

Challenge: Finding A Non-destructive Method of Leaf Area Measurement

The scientists first collected seeds from five populations/ecotypes along a wet gradient and germinated them. Seedlings were then grown in a greenhouse.

The seedlings from each population were separated into seven groups, each of which received seven levels of light: 10, 20, 30, 50, 60, 70, and 100%. The group receiving 100% light was grown in the open, while others were shaded with plastic in the greenhouses.

Each light level had 150 seedlings, with 30 from each ecotype. Data was collected after the seedlings were nine months old.

The scientists wanted to collect data on leaf length, width, area, perimeter, length-to-width ratio, and leaf dry weight.

Their sample pool was all leaves in three sample seedlings from each of the five ecotypes grown under seven light levels. So, all leaves from 105 seedlings had to be measured for leaf traits.

The scientists needed a method to measure the physical traits that would be precise and non-destructive, yet fast, as they had many leaves to measure!

The traditional grid count and gravimetric methods are simple and do not need many tools. However, they involve tracing each cut leaf and then making measurements. These methods would cost the scientists a lot of time and would be destructive and laborious.

Methods such as image processing and regression models are also time consuming and difficult. Regression involves making manual measurements of length and width and then finding a regression model to calculate leaf area.

The scientist also wanted to measure other parameters like length-to-width ratio, leaf specific area, and total leaf area of a seedling.

Solution: The CI-202 Portable Laser Area Meter

Given the vast sample size and number of parameters needed, the scientist decided to choose an instrument that could collect all the data they wanted, non-destructively.

Keeping these requirements in mind, they chose to use the CI-202 Portable Laser Leaf Area Meter. The device collects leaf measurements with a high-resolution laser scanner.

The leaf area meter measures all the leaf traits the scientists needed: leaf length, width, area, and perimeter.

The scientists first measured crown length in two directions and the height of the lowest leaf. Then, they used the CI-202 Portable Laser Leaf Area Meter to non-destructively measure the leaf traits of all leaves on a seedling.  

They placed the leaf on the detachable palette, under the transparent protective sheath, which smoothens curled leaves, making measurements precise. Then, they slid the scanner over the palette.

Scanner movements over every millimeter are detected by a control unit and added to the length and width. The measurements are constantly updated in the preloaded formulae for the leaf area. The device also simultaneously calculated the aspect ratio (or leaf length-to-width ratio).

The laser scanner has an LCD screen, so scientists could read the leaf trait measurements immediately.

The built-in data logger stored up to 8,000 data points, allowing scientists to finish data collection of all samples in three days.

After the leaf trait measurements, the scientists harvested the leaves to estimate the leaf dry weight for each seedling by oven drying at 70oC.

Benefits of Using the CI-202 Portable Laser Area Meter

The biggest advantage the scientists had of using the CI-202 Portable Laser Leaf Area Meter was that all the leaf traits were measured by a single tool.

Moreover, the leaf area meter manufactured by CID Bio-Science Inc is a light and portable device that can be used conveniently outside a laboratory.

Regardless of the shape of leaves, the scientists were assured that the leaf area measurements were precise. Getting all the calculations simultaneously during data collection also saved the scientists a lot of time.

The tool was simple to use and did not need any calibration, and the CI-202 has a data logger and supports easy USB data transfer.

An internal rechargeable battery could take 250 scans, helping to finish the task quickly.

Since the device was non-destructive, the leaves could be harvested together after all measurements were made. Thus, the scientists were assured that dry weight tests were accurate. 

Morphological Plasticity in Trees Response to Light Gradients

The scientists found that seedlings growing under low light allotted more resources to producing leaves. These seedlings had more leaf dry mass, leaf area, leaf area ratio, and specific leaf area; see Figure 1. The seedlings were trying to increase leaf size to intercept more sunlight. They also had a wider crown size to reduce self-shading. This was seen regardless of the ecotypes they came from.

Seedlings that were grown in high light conditions had reduced leaf area, leaf length, leaf, width, total leaf area, and leaf number. The scientists reasoned that seedlings do this to reduce transpiration when rate rises due to high radiation and temperature.

The scientists found that all seedlings exposed to the same light, however, did not show the same trend in all traits. Leaf area and crown area, depth, and length increased with increasing light in seedlings from wet ecotypes than those from drier ecotypes; see Figure 1. So, in wet areas, light is more deficient and is the driving factor for growth, while in dry areas, the trees are trying to maximize water use.

Plasticity was high for all morphological traits, yet seedlings reflected their original traits characteristic of their ecotypes.

Morphological Plasticity Matters

The scientists were able to show that physical and morphological plasticity exists and can be important for trees to adjust to variations in their environment, up to a certain extent. This has important implications for forestry management, and studies like this one are all the more accessible, thanks to precise, user-friendly forestry technology like the Portable Laser Leaf Area Meter.

—

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

Feature image courtesy of Robert Couse-Baker

Sources

Babei, F., Jalali, S.G., Sohrabi, H., & Shirvany, A. (2017). Variability in leaf and crown morphology correlated with light availability in five natural populations of Quercus castaneifolia C.A. Mey. Journal of Forest Science, 63(6): 275–281. doi: 10.17221/138/2016-JFS

Blanco, F. F., & Folegatti, M. V. (2003). A new method for estimating the leaf area index of cucumber and tomato plants. Horticultura Brasileira, 21(4), 666-669. doi:10.1590/s0102-05362003000400019
Chaudhary, P., Godara, S., Cheeran, A. N., & Chaudhari, A. K. (2012). Fast and Accurate Method for Leaf Area Measurement. International Journal of Computer Applications, 49(9), 22-25. doi:10.5120/7655-0757