Ever wondered how a simple leaf manages to capture sunlight and convert it into life-giving energy? It’s not just about being green; it’s about intricate biological and optical systems working together to support photosynthesis—the process that powers plant growth. Understanding how leaves harness light can help us grow healthier crops, design better agricultural systems, and optimize plant growth, whether it’s in your backyard or in high-tech greenhouses.
Let’s dive into how plant leaves function like mini solar panels and learn about the fascinating mechanisms that allow them to thrive under various conditions.
How a Leaf Captures Light: The Basics
Leaves are the powerhouse of plants, and their main job is to capture light energy and turn it into carbohydrates through photosynthesis. But there’s more going on beneath the surface!
At the leaf level, several mechanisms control how light is absorbed and managed. The leaf adjusts its absorption both across the whole leaf and within its different layers to maximize efficiency. These clever strategies include the leaf’s orientation, mesophyll (internal leaf structure), chloroplast movement, and light-absorbing pigments. Let’s break it down:
1. Leaf Orientation and Light Absorption
Leaves aren’t static—they actually move to optimize light capture. This process, known as heliotropism, involves the leaf adjusting its angle based on the direction of light. By tracking the sun, plants maximize light absorption without taking in too much light, which could cause damage.
When light hits a leaf, not all of it gets absorbed. Some light bounces off the surface or passes through without being used. However, leaves have evolved structures like the waxy cuticle and the arrangement of cells inside to control how much light is captured or reflected.
Actionable Tip:
Consider plant spacing in fields or greenhouses. Ensure plants can move or be arranged to get maximum sunlight exposure without shading each other.
2. The Inner Workings: Mesophyll and Chloroplasts
Inside the leaf, two layers of cells—palisade and spongy mesophyll—play key roles in photosynthesis. These layers are like light filters. The palisade layer, located just beneath the surface, is densely packed with chloroplasts (the tiny structures where photosynthesis occurs). As light penetrates the leaf, it’s mostly absorbed here.
Any light that doesn’t get absorbed by the upper layer bounces around in the loosely packed spongy layer. This scattered light gives the leaf a second chance to capture photons and turn them into energy.
Chloroplasts also move within the cells depending on how much light they’re getting. In low light, they spread out to catch more rays, but when it’s too bright, they shift to avoid overexposure. This ensures plants use light efficiently.
Actionable Tip:
Monitor light intensity in greenhouses and adjust artificial light to match the natural needs of the plants. Don’t overdo it—too much light can waste energy or harm the plants.
3. Pigments: Nature’s Solar Cells
The green color we see in leaves comes from chlorophyll, the primary pigment responsible for absorbing light. However, chlorophyll doesn’t work alone. Two types of chlorophyll, Chl a and Chl b, work together to capture light, especially in the blue and red parts of the spectrum.
Other pigments, like carotenoids, absorb light in different parts of the spectrum, especially in the blue range. They act as backup systems to transfer light energy to chlorophyll or even dissipate excess energy as heat when the leaf gets too much light, preventing damage. Think of carotenoids as the leaf’s safety net.
There are also flavonoids, which absorb UV light and protect the leaf from harmful radiation. These pigments don’t contribute to photosynthesis directly but help keep the leaf healthy and functional.
Actionable Tip:
When choosing grow lights, ensure the spectrum matches the absorption needs of plants. Blue and red wavelengths are essential, while UV protection may be required for sensitive crops.
4. Photosynthesis and Beyond
Photosynthesis is more than just light absorption; it also involves the movement of carbon dioxide (CO2) and water. During photosynthesis, CO2 enters the leaf, and water vapor is released in a process called transpiration. Meanwhile, the sugars produced by photosynthesis are transported to other parts of the plant in a process known as translocation.
The balance between these processes is key to a plant’s overall health and productivity. If conditions like light, water, or CO2 levels aren’t right, the plant’s ability to perform photosynthesis is compromised.
Conclusion: Key Takeaways
To wrap it all up, a leaf’s ability to harness light and turn it into energy depends on a variety of clever biological mechanisms. By understanding these processes, you can optimize plant growth and health, whether you’re managing a small garden or a large agricultural setup.
Here’s a quick summary of what we’ve learned:
- Leaf movement (heliotropism) optimizes light capture.
- Mesophyll layers manage how light penetrates and gets absorbed.
- Chloroplasts adjust their position to balance light intake.
- Pigments like chlorophyll, carotenoids, and flavonoids absorb and protect against light.
- Transpiration and translocation support photosynthesis by balancing water, CO2, and sugar movement.
By paying attention to these factors, you can help plants perform their best, from light absorption to growth.
Infographic Summary for Canva:
- Leaf Orientation: Adjusts to light direction (Heliotropism)
- Chloroplast Movement: Shifts to balance light absorption
- Key Pigments: Chlorophyll, Carotenoids, Flavonoids
- Photosynthesis Helpers: Transpiration (water loss), Translocation (sugar movement)
- Actionable Tips: Optimize plant spacing, monitor light intensity, choose proper light spectrum
Understanding and leveraging these natural processes will help you grow healthier, more productive plants!
The section you’ve shared discusses several critical aspects of photosynthesis and plant physiology, with a focus on light absorption and its effects on photosynthesis efficiency, especially when different light wavelengths are involved.
- Green Light and Photosynthesis: While green light (GL) is less absorbed compared to blue and red light, it plays a more significant role in photosynthesis than originally assumed. Due to the scattering effect within the leaf, GL can penetrate deeper into the leaf, reaching chloroplasts that are not yet light-saturated, thus enhancing the overall photosynthetic rate. This deep penetration and scattering compensate for its lower absorbance.
- Electron Transport and Carbon Assimilation: Photosynthesis consists of two main processes:
- Electron Transport: Light energy is converted into NADPH and ATP, essential for carbohydrate synthesis.
- Carbon Assimilation: CO2 is fixed into sugars via the Calvin cycle, with the help of ATP and NADPH generated in electron transport.
- Light Scattering and Leaf Photosynthesis: Due to leaf scattering, transmitted light to lower leaves tends to be enriched in green and far-red light, which triggers light acclimation responses in plants. The scattering increases photon absorption chances, driving photosynthesis even under green light.
- Transpiration: This is essential for water movement through the plant and involves the evaporation of water from the leaf surfaces. The regulation of stomatal openings is crucial for balancing CO2 uptake with water loss. Too much or too little transpiration can affect plant growth, causing issues such as blossom-end rot or tipburn, particularly in greenhouse environments.
- Translocation: Photosynthates like sucrose are transported from source organs (e.g., mature leaves) to sink organs (e.g., fruits and growing tissues). Proper management of the source-sink balance ensures optimal photosynthesis and enhances yield quality.
This discussion is essential in understanding how light wavelengths, especially with the application of LEDs in horticulture, affect leaf photosynthesis and whole-plant growth. It highlights that green light, often considered less important, plays a unique role in reaching deeper leaf chloroplasts and supporting photosynthesis in lower leaves.
This excerpt on “Optical and Physiological Properties of a Plant Canopy” by Yasuomi Ibaraki highlights key factors in the interaction of light with plant canopies and how these interactions impact photosynthesis and plant growth.
Key Concepts:
- Canopy Definition: The canopy refers to the collective mass of leaves of multiple plants, forming a layer above the ground. The structure and spatial organization of this canopy influence light distribution, absorption, and photosynthesis.
- Photosynthetic Photon Flux Density (PPFD): PPFD measures the density of light particles (photons) within a given area that are available for photosynthesis. Its distribution within the canopy is critical because different leaves receive varying light intensities, impacting overall canopy photosynthesis and plant growth.
- Light Attenuation: As light penetrates through a canopy, it diminishes in intensity due to reflection and absorption by leaves. This process is mathematically modeled using an extinction coefficient, kkk, which factors in leaf area index (LAI) and the geometrical structure of the canopy. The attenuation of light follows an exponential decay pattern, similar to Beer’s Law in physics.
- Leaf Area Index (LAI): LAI is the ratio of the total leaf area to the ground area. It is a key factor in understanding light distribution within the canopy. The larger the LAI, the denser the canopy, and hence, the more light is absorbed and less reaches the ground.
- Extinction Coefficient kkk: This coefficient varies with species and canopy structure. It is higher when light is absorbed more rapidly within a dense canopy and lower when light penetrates deeply. The table provided in the text lists values for different plant species, showing how the structure of leaves (erect, horizontal, etc.) affects kkk.
- Light Spectral Distribution: The spectral distribution of light within a canopy differs from that outside, as leaves selectively absorb and reflect certain wavelengths. This spectral shift is important in assessing photosynthesis at different depths of the canopy.
- Artificial Lighting Considerations: The light environment in controlled plant production settings (e.g., urban agriculture, greenhouses) may differ due to the spectral qualities of artificial lights. The angle and direction of artificial lighting can also affect how light is distributed within the canopy.
Methods:
- Modeling Canopy Photosynthesis: To estimate total canopy photosynthesis, researchers sum up the individual photosynthetic rates of small leaf sections under uniform conditions. Extinction coefficients are applied to account for the gradual decrease in light intensity within different layers of the canopy.
In conclusion, understanding the light environment within a plant canopy is essential for optimizing plant growth and productivity, especially when using artificial lighting systems in agricultural settings. The extinction coefficient and LAI are key parameters for modeling light attenuation and photosynthesis across various plant species and canopy structures.
Consideration of Spectral Properties Within the Canopy
The spectral properties of light within a plant canopy are notably different from those outside due to the absorption and reflection of specific wavelengths by the leaves. Green and far-red light tend to increase within the canopy because leaves reflect and transmit light in these spectral ranges. This effect is more pronounced under artificial lighting, especially when narrowband LED lamps are used. LEDs often lack green and far-red wavelengths, leading to significant differences in light spectra compared to natural sunlight.
Green Light Penetration
Green light has a greater capacity to penetrate deeper into plant canopies, potentially reaching lower layers of leaves and thus increasing the overall photosynthesis of the canopy. This characteristic is beneficial because the lower layers of the canopy, which receive less light due to shading from upper leaves, can still contribute to photosynthesis when exposed to green light.
Far-Red Light and Morphogenesis
Far-red light, while less significant for photosynthesis, plays a role in plant morphogenesis. It influences processes like shade avoidance and elongation growth, affecting the overall structure of the plant.
Influence of Light Spectrum on Extinction Coefficient
The spectral properties of light sources can affect the extinction coefficient kkk and the distribution of photosynthetically active photon flux density (PPFD) within the canopy. Blue and red light, commonly used in LED grow lights, result in a higher extinction coefficient, meaning that light penetrates less deeply into the canopy, reducing the PPFD in lower layers.
9.5 Canopy Photosynthesis
9.5.1 Characteristics of Canopy Photosynthesis
Canopy photosynthesis, which determines plant biomass accumulation, is influenced by several factors such as the light environment, CO2 concentration, temperature, humidity, and air flow. The photosynthetic properties of a canopy differ from those of individual leaves, especially in how they respond to light. For example, in a well-developed canopy, light at the top may be saturated for photosynthesis, but lower layers can still benefit from additional light, leading to overall increased photosynthesis.
The PPFD distribution within the canopy is critical in this regard. The light-photosynthetic curve for a canopy often shows higher or no saturation points compared to a single leaf because of the contribution of lower canopy layers where photosynthesis continues even when the upper layers are saturated.
9.5.2 Simple Method for Estimating Canopy Photosynthetic Rate
A basic method for estimating the photosynthetic rate of a canopy is by summing the photosynthetic rates of smaller portions of the canopy, each assumed to experience uniform environmental conditions, especially uniform PPFD. This allows for an estimation of average photosynthetic rates across different canopy layers.
One simple approach for this is using the extinction coefficient kkk to estimate PPFD within various canopy layers. The absorbed PPFD per unit leaf area at any horizontal layer can be calculated using the following expression:I0=dIdF(1−τ)I_0 = \frac{dI}{dF}(1 – \tau)I0=dFdI(1−τ)
Where:
- I0I_0I0 is the photon flux density at the top of the layer.
- τ\tauτ is the leaf transmittance.
- dI/dFdI/dFdI/dF represents the rate of change of PPFD as a function of cumulative LAI.
In this method, Monsi and Saeki (2005) proposed that by calculating the absorbed PPFD for each layer, the overall photosynthetic rate of the entire canopy can be estimated more accurately.
Conclusion
The spectral distribution of light within a plant canopy, particularly in artificial environments, has significant implications for both light penetration and overall photosynthesis. Green and far-red light can enhance photosynthesis in lower canopy layers, and the extinction coefficient kkk is crucial for modeling how light attenuates through the canopy.
Canopy Photosynthesis Estimation (continued)
The average photon flux density I0I_0I0 at a given horizontal layer is expressed by the equation:I0=I0kekF(1−τ)I_0 = I_0 k e^{kF}(1 – \tau)I0=I0kekF(1−τ)
Here, I0I_0I0 serves as an input to models relating net photosynthetic rates to PPFD. Various functions can describe this relationship, typically showing convex curves with saturation points for photosynthesis. Monsi and Saeki (2005) proposed a rectangular hyperbolic function defined by the equation:p=aI0(1+bI0)−1−rp = aI_0 \left( 1 + bI_0 \right)^{-1} – rp=aI0(1+bI0)−1−r
where:
- ppp is the net photosynthetic rate,
- aaa and bbb are constants,
- rrr is the rate of dark respiration.
Substituting I0I_0I0 from the previous equation into this function allows us to express canopy photosynthesis PPP as:P=akbln(11−τkbI0)+1−τkbI0ekF−rFP = \frac{a}{k_b} \ln\left( \frac{1}{1 – \tau k_b I_0} \right) + \frac{1 – \tau}{k_b} I_0 e^{kF} – rFP=kbaln(1−τkbI01)+kb1−τI0ekF−rF
This equation enables the estimation of the optimal Leaf Area Index (LAI) that maximizes canopy photosynthesis, as highlighted by Hirose (2004). However, this approach assumes that the photosynthetic properties of individual leaves are uniform throughout the canopy. In reality, leaves positioned lower in the canopy, where PPFD is lower, often exhibit the characteristics of shade leaves, with high photosynthetic rates at low PPFD but lower saturation rates. Therefore, models that consider the distribution of leaf photosynthetic properties, such as those proposed by Hirose and Werger (1987), may provide more accurate estimates.
Simplified Canopy Photosynthesis Models
Jones (1992) identified two specific scenarios where simpler models can effectively estimate canopy photosynthesis:
- Acute Leaf Angle Scenario:
- If all leaves are oriented at an acute angle to direct radiation, total canopy photosynthesis correlates with light interception, expressed as: Pcanopy=ϵpI0P_{\text{canopy}} = \epsilon_p I_0Pcanopy=ϵpI0
- At high LAIs, where all radiation is intercepted, canopy photosynthesis simplifies to ϵpI0\epsilon_p I_0ϵpI0.
- Low LAI Canopies:
- For canopies with very low LAIs, the photosynthetic models for individual leaves can be applied without complex adjustments.
9.5.3 Growth Analysis
Another approach to estimate canopy photosynthesis involves growth analysis, which assesses biomass accumulation over time. The Relative Growth Rate (RGR) is a common metric used for this purpose:RGR=1WdWdtRGR = \frac{1}{W} \frac{dW}{dt}RGR=W1dtdW
Where:
- WWW is the dry weight of the plant (in grams),
- ttt is the time in days.
The Net Assimilation Rate (NAR), representing growth rate per unit leaf area, can be derived from the following equation and is directly related to the photosynthetic rate:NAR=1LdWdt(g m−2 d−1)NAR = \frac{1}{L} \frac{dW}{dt} \quad \text{(g m}^{-2} \text{ d}^{-1}\text{)}NAR=L1dtdW(g m−2 d−1)
Where LLL represents leaf area (in square meters).
Assuming a constant RGR during a specific period, it can be calculated from dry weights W1W_1W1 and W2W_2W2 and leaf areas L1L_1L1 and L2L_2L2 measured at different times t1t_1t1 and t2t_2t2:RGR=ln(W2/W1)t2−t1RGR = \frac{\ln(W_2/W_1)}{t_2 – t_1}RGR=t2−t1ln(W2/W1)
The NAR can also be expressed in relation to leaf areas:NAR=(W2−W1)(L2−L1)(t2−t1)(g m−2 d−1)NAR = \frac{(W_2 – W_1)}{(L_2 – L_1)(t_2 – t_1)} \quad \text{(g m}^{-2} \text{ d}^{-1}\text{)}NAR=(L2−L1)(t2−t1)(W2−W1)(g m−2 d−1)
The Leaf Area Ratio (LAR) connects RGR and NAR:RGR=NAR×LARRGR = NAR \times LARRGR=NAR×LAR
Where:LAR=LWLAR = \frac{L}{W}LAR=WL
Non-destructive Measurements
While growth analysis often relies on destructive sampling for measuring dry weight or leaf area over time, Relative Leaf Growth Rate (RLGR) can be estimated non-destructively through imaging:RLGR=ln(L2/L1)t2−t1RLGR = \frac{\ln(L_2/L_1)}{t_2 – t_1}RLGR=t2−t1ln(L2/L1)
For instance, RLGR was automatically estimated for Arabidopsis thaliana using image analysis (Arvidsson et al., 2011). If a linear relationship exists between the projected area from an image and the actual leaf area, RLGR can be simply estimated from image data, facilitating phenotyping and growth analysis without the need for physical sampling (Ibaraki and Dutta Gupta, 2014).
Summary
Understanding the spectral properties of light and employing models for estimating canopy photosynthesis and growth analysis are essential for optimizing plant production systems. By integrating these methods, researchers can improve growth management strategies in various agricultural contexts.
Evaluation of Spatial Light Environment and Plant Canopy Structure
Yasuomi Ibaraki
Abstract
Understanding the light environment is crucial for enhancing plant production efficiency in plant factories. The plant canopy structure significantly influences the distribution of photosynthetic photon flux density (PPFD), which in turn affects plant growth. Therefore, comprehending and managing the canopy structure is essential for effective plant production. Key indices for assessing canopy structure include the extinction coefficient, leaf area index (LAI), leaf area density (LAD) distribution, and leaf angle distribution. LAI is vital for evaluating both plant growth and the canopy’s light environment. Numerous indirect yet non-destructive methods for estimating LAI have been developed, including plant canopy analyzers (PCA), hemispherical photography, terrestrial laser scanners (TLS), spectral reflectance, and image analysis. Additionally, the canopy surface exhibits a PPFD distribution influenced by variations in leaf inclination and orientation. This chapter introduces a straightforward method for assessing PPFD distribution on the plant canopy surface using reflection images, successfully creating PPFD histograms for several plant species under various lighting conditions.
Keywords: Canopy surface, Image analysis, Leaf angle, LAI, PPFD, Quantum sensor, Reflection image
10.1 Introduction
The light environment, particularly the distribution of photosynthetic photon flux density (PPFD; μmol m² s⁻¹), is critical for biomass productivity. Properly understanding this distribution is vital for improving plant production efficiency in plant factories. Light is absorbed by leaves, leading to a vertical PPFD distribution within the plant canopy. Moreover, variations in leaf inclination and orientation result in a distinct PPFD distribution on the canopy surface. Accurately measuring the PPFD on leaf surfaces is essential for evaluating plant photosynthetic status, especially when using remotely acquired images.
This chapter discusses methods for evaluating the PPFD distribution within and on the plant canopy, along with the assessment of canopy structure and leaf area, which are crucial for determining the PPFD distribution in a canopy.
10.2 Measurement of PPFD Distribution in a Plant Canopy
In plant production, “light intensity” on leaf surfaces is often assessed as PPFD using quantum sensors. PPFD is preferred for evaluating light intensity in plant production due to its provision of direct information regarding photon availability for photosynthesis, assuming photons in the range of 400 to 700 nm can be equally utilized for this purpose. Although this assumption may not be strictly accurate, it is practical for use. The relationship between irradiance and PPFD remains constant under identical light source conditions, allowing conversion between the two metrics.
Various types of quantum sensors—point, line, and globe-type—can measure PPFD. However, determining the PPFD distribution on leaves at the canopy surface is challenging due to dynamic variations in solar radiation and significant differences in leaf angle and orientation. In plant factories using artificial lighting, dynamic PPFD variations are less common. Here, spatial distribution can be measured with a point sensor, albeit in a time-consuming and labor-intensive manner. Line sensors can estimate average PPFD over an area, while globe-type sensors are designed to measure light from all directions, making them suitable for evaluating light intensity in plant cultivation involving combined sideward and downward lighting.
10.3 Evaluation of Plant Canopy Structure
The plant canopy structure influences the PPFD distribution and thus plays a crucial role in plant growth. Understanding and managing the canopy structure is essential for effective plant production. However, evaluating canopy structure can be complex due to the spatial distribution patterns of leaves and their growth-related changes. The extinction coefficient kkk provides insights into canopy structure and can be estimated through measurements of vertical PPFD distribution and leaf area index (LAI). Yet, measuring PPFD distribution may not be practical if the primary goal is to characterize canopy structure. kkk can also be estimated under the assumption of vertical uniformity using only photosynthetically active radiation (PAR) measurements above and below the canopy, along with LAI estimation.
Leaf angle distribution is another key component of canopy structure, typically determined using a clinometer, although this method is labor-intensive and time-consuming. Canopies can exhibit various orientations, such as planophile (predominantly horizontal leaves) and erectophile (predominantly vertical leaves). The ellipsoidal leaf angle density function is often utilized to approximate real plant canopies, expressing the probability density of leaf angle based on the assumption of a similar angular distribution to that of an ellipsoid.
Other significant indices for evaluating canopy structure include LAI and leaf area density (LAD). While LAI measures the total leaf area in the canopy, it also provides insights into canopy structure. In contrast, LAD (m¹) represents total one-sided leaf surface area (m²) per unit volume (m³) within the canopy, with the integral of LAD up to canopy height yielding LAI. Understanding the vertical distribution of LAD is instrumental in analyzing PPFD distribution.
10.4 LAI Estimation
10.4.1 Direct and Indirect Estimation
LAI is defined as the total projected leaf area (one side only) per unit area of ground and is crucial for both plant growth and evaluating the canopy’s light environment. Direct measurements of LAI involve destructive methods, such as detaching leaves from a specific ground area and measuring their area. This destructive sampling method poses challenges for time-course analysis. Therefore, developing non-destructive methods is essential. Rough estimations can be made by measuring the number of leaves and the area of representative leaves.
Several indirect but non-destructive methods have been proposed, including plant canopy analyzers, hemispherical photography, terrestrial laser scanners, spectral reflectance, and image analysis.
10.4.2 Methods Using Gap Fraction
The plant canopy analyzer (LI-COR, LAI-2200) provides a non-destructive means of estimating LAI by measuring light above and below the canopy and determining canopy light interception at five angles. Canopy gap fraction—defined as the probability of light passing through the canopy without encountering leaves or other plant elements—is an important index for analyzing forest canopies. This index can be measured using hemispherical photography or laser scanners.
For hemispherical photography, images are taken with a circular fish-eye lens from below the canopy. Gap fractions are calculated by determining the fraction of exposed background within concentric rings around the image’s center. Terrestrial laser scanners (TLS) use range-finding techniques to establish 3D positions of objects within the scanner’s field of view, enabling gap fraction estimation from the recorded return of laser “shots.” Moreover, laser scanning can directly estimate vertical LAD distribution.
10.4.3 The Use of Spectral Reflectance
Methods utilizing spectral reflectance focus on the relationships between vegetation indices or reflectance in specific wavelength regions. Plant leaves absorb red light while reflecting near-infrared (NIR) light; thus, canopies with more leaves exhibit lower reflectance in the red region and higher reflectance in the NIR. By measuring reflectance in these regions, LAI can be estimated. The normalized difference vegetation index (NDVI) is widely used for evaluating plant cover in remote sensing and can serve as a proxy for estimating LAI.
10.4.4 Image Analysis
Image analysis using digital cameras allows for the non-destructive acquisition of object size information. Projected areas can be measured from images, and if a linear relationship exists between projected and actual leaf area, LAI can be estimated using image analysis. Various studies have demonstrated the effectiveness of digital photography in LAI estimation for different crops.
10.5 Estimation of PPFD Distribution on Plant Canopy Surface
10.5.1 Importance of Understanding Light Distribution on the Canopy Surface
Non-destructive methods for evaluating plant photosynthetic properties using remotely acquired images have gained popularity in environmental control. A comprehensive understanding of irradiance/photon flux density distribution on the canopy surface is essential. Parameters derived from chlorophyll fluorescence measurements, such as PSII quantum yield, depend on PPFD on leaves, highlighting the necessity for accurate PPFD evaluation. Moreover, leaf irradiance impacts leaf temperature and can limit plant stress evaluation.
10.5.2 Reflection Image-Based Estimation Method of PPFD on Canopy Surface
Reflection images of plant canopies were acquired using various cameras equipped with band-pass filters to improve correlation between PPFD and pixel values. To minimize specular reflection, images were captured from multiple angles. Prior to imaging, the linearity of the output (pixel value) and input (PPFD) should be confirmed for each camera, and if necessary, gamma correction is applied. Research has shown linear relationships between actual PPFD and pixel values across different plant canopies, under both natural and artificial lighting. However, the regression model’s slope and intercept vary by canopy type, necessitating unique regression models for each measurement.
Based on these findings, a simple method for estimating PPFD distribution on plant canopies was developed. This method involves measuring actual PPFD at a point on the canopy surface, using it to create a linear regression model for calculating PPFD from pixel values in the reflection image. This approach demonstrates potential for practical applications in greenhouse environments, enhancing the understanding of light distribution and its impact on plant growth.
This summary provides an overview of the methods and implications related to evaluating the spatial light environment and plant canopy structure, highlighting their significance in improving plant production efficiency in controlled environments.
structured summary of the content provided, focusing on the key applications and methodologies regarding PPFD (Photosynthetic Photon Flux Density) estimation, lighting efficiency in plant production, and the assessment of light energy received by plants.
Applications of PPFD Estimation
- PPFD Histogram Construction:
- Research by Ibaraki et al. (2012a):
- Constructed PPFD histograms of tomato plant canopies using reflection images.
- Implemented gamma correction on pixel values, converting them to PPFD using a linear model based on observed PPFD and pixel value relationships.
- Noted temporal changes in PPFD histograms on tomato canopies throughout the day.
- Research by Ibaraki et al. (2012a):
- Android Application Development:
- Miyoshi et al. (2016):
- Developed an Android app for real-time PPFD distribution estimation on plant canopies.
- The application uses reflection images captured by a tablet.
- It employs a thresholding method based on luminance and green channel values (G/(R+G+B)) to extract plant canopy areas.
- Histograms from three directional images are averaged for analysis.
- Example shown in Fig. 10.10 demonstrates PPFD distribution on lettuce canopies under artificial lighting.
- Miyoshi et al. (2016):
Evaluation of Lighting Efficiency in Plant Production
- Importance of Lighting Efficiency:
- As artificial lighting use in plant production rises, assessing lighting efficiency becomes critical due to energy costs.
- Key to efficiency is the amount of biomass produced per unit of energy used for plant irradiation.
- Methods for Evaluating Lighting Efficiency:
- Energy Conversion Efficiency:
- Comparing biomass production against energy used for irradiation.
- Light Use Efficiency (LUE):
- Defined as the ratio of accumulated biomass to the photosynthetically active radiation (PAR) absorbed.
- Varies with crops and is influenced by factors like nitrogen status and environmental conditions.
- Energy Conversion Efficiency:
- Utilization Factor:
- The ratio of PAR received by the plant canopy (PARP) to the total PAR emitted from the lamps (PARL).
- Changes over time depending on lamp properties and canopy structure.
- Improving this ratio reduces unnecessary irradiation, energy consumption, and production costs.
Table of Light Use Efficiency (LUE) for Various Crops
| Species | LUE Value (μg J⁻¹) | Description | Reference |
|---|---|---|---|
| Tomato | 2.8–4.0 | Light use efficiency | Dorais (2003) |
| Sweet Pepper | 2.1 | Light use efficiency | Dorais (2003) |
| Lettuce | 1.44–2.43 | Conversion efficiency of absorbed PAR | Tei et al. (1996) |
| 1.26 | Radiation conversion efficiency | Javanovic et al. (1999) | |
| Onion | 0.99–5.08 | Conversion efficiency of absorbed PAR | Tei et al. (1996) |
| 1.08 | Radiation conversion efficiency | Javanovic et al. (1999) | |
| Rice | 4.15 | Efficiency of light utilization for DM production | Sands (1999) |
| Maize | 3.4 | Efficiency of light utilization for DM production | Sands (1999) |
| Soybean | 1.29 | Efficiency of light utilization for DM production | Sands (1999) |
This summary encapsulates the advancements in estimating PPFD, methodologies for evaluating lighting efficiency in plant production, and the importance of light energy received by plants, supporting improved agricultural practices under artificial lighting conditions.
Improving Electrical Energy Use Efficiency
In crop production under artificial lighting, estimating electrical energy use efficiency (EEUE) is essential for evaluating lighting effectiveness. The estimation methods are elaborated in Chapter 29. Various approaches can enhance EEUE (Kozai, 2013):
- Improving Light Source Efficiency: Utilize light sources with high luminous efficacy (lm/W), such as advanced LEDs, which are explored in detail in Chapter 29.
- Enhancing the PARP/PARL Ratio: The ratio of Photosynthetically Active Radiation absorbed by plants (PARP) to that emitted by the light source (PARL) can be improved by minimizing unnecessary light dispersion. This can be achieved through:
- Well-Designed Reflectors: Reflectors can direct backward light forward or laterally to reduce light loss.
- Reducing Distance Between Lamps and Plants: Decreasing this distance minimizes light emitted outside the plant canopy.
- Controlling Lighting Direction: Tailoring the lighting direction according to the plant canopy structure enhances efficiency.
- Improving Light Use Efficiency (LUE): This can be achieved by optimizing light application timing and controlling irradiated areas:
- Interplant Lighting: This technique directs light to lower leaves that may not receive adequate light from overhead sources, potentially increasing LUE (Kozai, 2013; Massa et al., 2008).
- Optimizing Lighting Timing: Timing the lighting effectively, such as during nighttime or end-of-day, can stimulate growth (Fukuda et al., 2004; Yang et al., 2012).
- Controlling Leaf Area Index (LAI): Adjusting planting density affects the PARP/PARL ratio and improves energy efficiency (Kozai, 2013; Yokoi et al., 2003).
11.3 Lighting Efficiency Based on PPFD Distribution on a Canopy Surface
The Photosynthetic Photon Flux Density (PPFD) on leaf surfaces is critical for plant production. A method for evaluating the efficiency of supplemental lighting through PPFD distribution on canopy surfaces was developed by Ibaraki and Shigemoto (2013). This method involves:
- Acquiring reflection images of the plant canopy from three angles using a digital camera.
- Estimating PPFD on leaf surfaces based on pixel values through a regression model aligned with simultaneous PPFD measurements.
The PPFD distribution histogram is analyzed by calculating:
- Average PPFD
- Median PPFD
- Coefficient of Variation (CV)
An integrated measure called Integrated PPFD per Unit Power Consumption (IPPC) is proposed to evaluate lighting efficiency:IPPC=Averaged PPFD(μmol m−2 s−1)×Projected leaf area(m2)Power consumption(W)\text{IPPC} = \frac{\text{Averaged PPFD} (\mu mol \, m^{-2} \, s^{-1}) \times \text{Projected leaf area} (m^{2})}{\text{Power consumption} (W)}IPPC=Power consumption(W)Averaged PPFD(μmolm−2s−1)×Projected leaf area(m2)
This allows for comparative analysis of lighting systems based on PPFD distributions influenced by light source type and canopy structure. Similar methodologies include energy efficiency calculations for LED systems in controlled environments (Bornwaβer and Tantau, 2012).
11.4 Plant Growth Modeling for Evaluating Lighting Efficiency
11.4.1 Simple Growth Model
Modeling plant growth is pivotal for comprehending light distribution and evaluating lighting efficiency. For vegetative growth, an exponential model is typically used, reflecting constant growth rates over time:W=W0eRGRtW = W_0 e^{RGR t}W=W0eRGRt L=L0eRLGRtL = L_0 e^{RLGR t}L=L0eRLGRt
where W0W_0W0 and L0L_0L0 are initial values of weight and leaf area, respectively. Growth can decline due to competition for resources, with various models adjusting for RGR based on environmental factors and plant physiology.
11.4.2 2D and 3D Modeling for Vegetative Growth
Advancements in modeling canopy structure and leaf distribution enhance the assessment of lighting efficiency. L-systems facilitate 3D modeling of plant architecture, simulating growth patterns based on rewriting rules. This method supports the analysis of leaf arrangement and light distribution, vital for calculating the PARP/PARL ratio.
Functional-Structural Plant Models (FSPMs) integrate 3D plant structure and physiological functions, often employing L-systems. These models have been utilized to compare lamp positioning scenarios, optimizing lighting strategies in greenhouse settings for crops like tomatoes (Visser et al., 2012; 2014).
Conclusion
Improving electrical energy use efficiency in crop production under artificial lighting involves a multifaceted approach that encompasses light source optimization, spatial and temporal control of light distribution, and effective modeling of plant growth. These strategies collectively enhance the sustainability and productivity of modern agricultural systems.
Effects of Physical Environment on Photosynthesis, Respiration, and Transpiration
Ryo Matsuda
Abstract
This study outlines the responses of plants’ photosynthesis, respiration, and transpiration rates to varying levels of physical environmental factors. Water vapor movement from a leaf to the atmosphere through transpiration is quantitatively described using a gas diffusion model, which incorporates the concentration gradient of water vapor and its conductance. Environmental factor changes directly affect transpiration rates by altering the water vapor diffusion driving force or indirectly by changing stomatal aperture. Plants exhibit two types of respiration: dark respiration and photorespiration, which are fundamentally different. Dark respiration rates are sensitive to temperature, gas concentrations, and light intensity. The influx of carbon dioxide (CO₂) during photosynthesis is divided into CO₂ diffusion from the atmosphere to chloroplasts and biochemical CO₂ fixation in the chloroplasts. The former can be modeled similarly to water vapor diffusion. Net photosynthetic rates in C₃ leaves display a saturating increase in response to rising CO₂ concentrations or photosynthetic photon flux density (PPFD), characterized by multiple parameters. The net photosynthetic rate is minimal at extreme temperatures, peaking at intermediate levels.
Keywords: CO₂ diffusion, conductance, environmental factors, flux, response curves, stomata, water vapor diffusion.
12.1 Introduction
Photosynthesis, respiration, and transpiration are vital physiological processes for plant growth and development, significantly influenced by environmental factors. In return, these processes facilitate the exchange of energy and compounds like water vapor and CO₂ between plants and the atmosphere, affecting the environment. Understanding the plant-environment interaction is essential for optimizing controlled environment agriculture, including facility design and operation and plant management practices.
This chapter provides an overview of the environmental impacts on the photosynthesis, respiration, and transpiration of green plants, focusing specifically on the physical environment, which includes light, temperature, humidity, and gas conditions. The discussion will concentrate on C₃ photosynthesis, as the majority of plants cultivated in greenhouses and plant factories with artificial lighting (PFAL) are C₃ species. For details on the physiological basis of photosynthesis, transpiration, and light spectral effects, refer to Chapter 8.
12.2 Transpiration
Transpiration from leaves is crucial for driving the transpiration stream in the xylem, facilitating water and nutrient uptake by roots. Environmental control of transpiration rates in greenhouses and PFAL is essential for maintaining optimal water and nutrient status in plants. Additionally, transpiration helps dissipate energy absorbed by leaves as latent heat. This section introduces a model for water vapor diffusion from the leaf to the atmosphere, summarizing the effects of various environmental factors on transpiration rates, particularly concerning stomatal responses.
12.2.1 Water Vapor Diffusion Model
Figure 12.1 illustrates water vapor and CO₂ diffusion between a leaf and the atmosphere. Water vapor in intercellular air spaces evaporates at the mesophyll cell surface, diffusing to the atmosphere through stomatal pores, with further diffusion to the free atmosphere through the leaf boundary layer. While water vapor may also move across the cuticle layer on the leaf epidermis, this is usually negligible compared to stomatal diffusion.
Water vapor diffusion can be quantitatively described using a model analogous to Ohm’s law. According to this principle, transpiration rate per unit leaf area (T [mol H₂O m² s⁻¹]) is proportional to the difference in mole fractions of water vapor at two representative points. Conductance is the inverse of resistance, often used in the model.
At steady state, T can be expressed as:
T=gwt(Hi−Ha)T = g_{wt}(H_i – H_a)T=gwt(Hi−Ha)
Where:
- HiH_iHi and HaH_aHa are the mole fractions of water vapor in intercellular air spaces and in the atmosphere beyond the leaf boundary layer, respectively.
- gwtg_{wt}gwt represents total water vapor conductance.
The total conductance can be divided into stomatal conductance (gwsg_{ws}gws) and leaf boundary layer conductance (gwbg_{wb}gwb), leading to:
1gwt=1gws+1gwb\frac{1}{g_{wt}} = \frac{1}{g_{ws}} + \frac{1}{g_{wb}}gwt1=gws1+gwb1
Using gwsg_{ws}gws and gwbg_{wb}gwb, T at steady state can also be written as:
T=gws(Hi−Hl)(Hl−Ha)T = g_{ws}(H_i – H_l)(H_l – H_a)T=gws(Hi−Hl)(Hl−Ha)
Where HlH_lHl is the mole fraction of water vapor immediately external to the leaf surface.
Environmental factor changes influence T directly (by altering the concentration gradient of water vapor) or indirectly (through changes in gwbg_{wb}gwb and/or gwsg_{ws}gws). For instance, gwbg_{wb}gwb decreases with increasing leaf boundary layer thickness, which is influenced by wind speed and leaf morphology. A variety of environmental changes cause rapid stomatal conductance responses within seconds to minutes, which influence both T and photosynthetic CO₂ assimilation—critical for carbon gain.
12.2.2 Effects of Humidity
Humidity directly influences T. Assuming the mole fraction of water vapor in intercellular air spaces, HiH_iHi, is saturated at leaf temperature (tlt_ltl), we can express it as:
Hi=es(tl)/pH_i = e_s(t_l)/pHi=es(tl)/p
Where es(tl)e_s(t_l)es(tl) is the saturated water vapor pressure at tlt_ltl, and ppp is atmospheric pressure.
Rewriting T using atmospheric water vapor pressure (eee) gives:
T=gwt(es(tl)−e)pT = g_{wt}\frac{(e_s(t_l) – e)}{p}T=gwtp(es(tl)−e)
Here, (es(tl)−e)(e_s(t_l) – e)(es(tl)−e) is termed the leaf-to-air water vapor pressure deficit (VPD). This shows that, if gwtg_{wt}gwt and ppp are constant, T is proportional to the leaf-to-air VPD. Thus, VPD is a more accurate measure than relative humidity for evaluating humidity’s effect on T.
Humidity also affects T indirectly via stomatal conductance; stomata tend to close under high VPD conditions. This decrease in stomatal conductance counteracts high leaf-to-air VPD’s direct effect on T.
12.2.3 Effects of Rhizosphere Environment
Water stress caused by moisture deficiency and excess salt accumulation in the rhizosphere can trigger stomatal closure. The phytohormone abscisic acid is a known inducer of stomatal closure. It is produced in roots during water shortage, transported to leaves via xylem sap, and induces stomatal closure, serving as a feedforward response to prevent excessive water loss.
12.2.4 Effects of Light Intensity and Spectrum
Stomatal conductance increases with higher PPFD, promoting transpiration and facilitating CO₂ uptake for photosynthesis under high light conditions. Additionally, it aids in evaporative cooling of leaves exposed to high radiative heat. The light-driven stomatal response occurs through two mechanisms: a blue light-dependent response mediated by the photoreceptor phototropin and a photosynthesis-dependent response likely driven by the photosynthetic activity of mesophyll cells and/or guard cells.
12.2.5 Effects of CO₂ Concentration
Stomatal conductance increases at low CO₂ concentrations and decreases at high concentrations. These changes help compensate for altered photosynthetic rates directly affected by CO₂ levels. Higher CO₂ concentrations also reduce water loss relative to CO₂ uptake through stomata, resulting in increased photosynthetic water-use efficiency, defined as the ratio of net photosynthetic rate to transpiration rate.
12.2.6 Effects of Temperature
Leaf-to-air VPD, which is influenced by leaf temperature, affects T. Changes in leaf temperature also affect photosynthetic and respiratory rates, indirectly influencing T via changes in stomatal conductance. Furthermore, higher temperatures lead to a reduction in leaf temperature due to latent heat loss, creating a complex interplay between leaf temperature and T. At steady state, leaf temperature and T are determined by the energy balance of the leaf.
12.3 Respiration
12.3.1 Dark Respiration and Photorespiration
Plants exhibit two types of respiration: dark respiration and photorespiration, which involve different metabolic pathways. Dark respiration includes glycolysis and the pentose phosphate pathway in the cytosol and plastids, followed by the tricarboxylic acid (TCA) cycle. The subsequent processes lead to energy production, which is critical for plant growth and functioning.
References
- Campbell, N.A., & Norman, J.M. (1998). Principles of Environmental Science.
- Jones, H.G. (2014). Plants and Microclimate: A Quantitative Approach to Environmental Plant Physiology.
- Lambers, H., et al. (2008). Plant Physiological Ecology.
Figure 12.1: Water Vapor and CO₂ Diffusion Model
This figure illustrates the cross-sectional view of a dorsiventral leaf, showing water vapor and CO₂ diffusion between the leaf and atmosphere, including various resistances and conductances.
Figure 12.2: Stomatal Conductance and Transpiration Rate
This figure displays stomatal conductance for water vapor at different incident PPFDs and the corresponding transpiration rates for spinach leaves, indicating the relationships between light intensity and these physiological responses.
This summary presents a comprehensive overview of the effects of physical environmental factors on plant processes such as photosynthesis, respiration, and transpiration, highlighting the complex interactions that govern plant responses to their surroundings.
This passage provides an in-depth overview of dark respiration and photosynthesis in plants, highlighting their physiological processes, environmental influences, and interconnections. Below is a summary that outlines the key points:
Dark Respiration vs. Photorespiration
- Dark Respiration:
- Occurs in all plant organs.
- Provides chemical energy and reducing power by oxidizing respiratory substrates (e.g., carbohydrates).
- Involves the Krebs cycle and oxidative phosphorylation in mitochondria.
- Can proceed in the light and dark.
- Its rate is influenced by temperature, oxygen (O₂), and carbon dioxide (CO₂) concentrations.
- Photorespiration:
- Specific to photosynthetic organisms, localized in chloroplasts, peroxisomes, and mitochondria.
- Aims to minimize carbon loss due to O₂ fixation in the Calvin cycle.
- Occurs only in the presence of light.
- Plants uptake O₂ and release CO₂ through both processes.
Effects of Temperature on Dark Respiration
- The rate of dark respiration increases almost exponentially between 10°C and 40°C.
- The Q10 model is often used to express the temperature dependence, where a 10°C increase in temperature leads to a twofold increase in respiration rate (Q10 ≈ 2).
- Lower temperatures are used in storage of perishable items, but excessive suppression of dark respiration in growing plants may hinder growth.
Effects of O₂ and CO₂ Concentrations
- Lower O₂ concentrations and higher CO₂ concentrations typically suppress dark respiration.
- In controlled environments (e.g., greenhouses), O₂ concentration is stable, affecting dark respiration little.
- CO₂ enrichment occurs during the day to enhance photosynthesis but is generally not high enough to significantly reduce dark respiration.
- In postharvest storage, reduced O₂ and increased CO₂ concentrations are used to prolong storage life.
Effects of Light Intensity
- Dark respiration rates in leaves decrease as light intensity increases.
- In the presence of light, the rate of respiration is lower than that in the dark, leading to the term “day respiration” for light-activated processes.
Photosynthesis Overview
- Photosynthesis converts CO₂ into carbohydrates using light energy and occurs in the chloroplasts.
- The net photosynthetic rate (Pn) can be calculated as: Pn=Pg−RdPn = Pg – RdPn=Pg−Rd Where:
- PgPgPg = gross photosynthetic rate
- RdRdRd = dark respiration rate
- Photosynthetic CO₂ uptake involves diffusion from the atmosphere to chloroplasts, characterized by resistances similar to those for water vapor diffusion.
CO₂ Diffusion Model
- CO₂ concentration is influenced by conductance factors, including boundary layer, stomatal, and mesophyll conductance.
- These conductances can be related to water vapor diffusion conductances.
Effects of CO₂ Concentration on Photosynthesis
- The net photosynthetic rate (Pn) in C3 plants typically increases in a saturating manner with rising CO₂ concentrations until reaching a saturation point (CSP).
- The CO₂ compensation point (CCP) is where Pn equals zero.
- CO₂ enrichment in controlled environments can significantly enhance Pn and biomass production.
Effects of Light Intensity on Photosynthesis
- Photosynthesis rate (Pn) increases with photosynthetic photon flux density (PPFD).
- Light saturation point (LSP) and light compensation point (LCP) define the PPFD levels at which Pn reaches maximum and zero, respectively.
- Leaves adapted to high light conditions (“sun” leaves) show higher LSP, LCP, and photosynthetic capacity compared to those in lower light (“shade” leaves).
Conclusion
The interplay of dark respiration and photosynthesis is critical for plant growth, influenced by environmental conditions such as temperature, light intensity, and gas concentrations. Understanding these processes helps in optimizing agricultural practices and improving crop yields.
t looks like you’ve provided a detailed excerpt on photosynthesis, transpiration, and the effects of air current on plant physiology. If you need help summarizing, analyzing, or discussing specific parts of the text, let me know how I can assist you! Here are some potential focuses based on your text:
- Summary: A concise summary of the key points discussed in the text.
- Analysis: A deeper dive into the implications of air movement on photosynthesis and plant health.
- Data Interpretation: Discussion or visualization of the figures referenced (like PPFD or air current speeds) and their significance.
- Research Context: A look into how this research fits into broader agricultural practices or plant science.
Please let me know how you’d like to proceed Certainly! Here are some key points continuing from the previous text, focusing on the importance of air movement, the effects of environmental factors, and their implications for plant growth and productivity:
Effects of Air Current Speed on Photosynthesis and Transpiration
- Enhanced Gas Exchange: Air movement reduces the resistance of the boundary layer around leaves, leading to improved gas exchange. This is critical for both photosynthesis (Pn) and transpiration (Tr), which are essential processes for plant growth.
- Threshold Speeds for Optimal Performance: Studies show that photosynthesis and transpiration rates increase significantly as air current speeds rise from 0.01 to about 0.3 m/s. Beyond this point (0.4 to 1.0 m/s), the rates tend to stabilize, indicating that certain speeds are optimal for gas exchange.
- Canopy vs. Single Leaf: The impact of air movement is more pronounced in plant canopies compared to single leaves due to the greater resistance created by the dense arrangement of leaves. Forced air circulation is vital in greenhouses and controlled environments to enhance overall plant growth.
Temperature and Humidity Control
- Temperature Regulation: Increased air current speeds help lower leaf temperatures due to enhanced transpiration, which helps maintain optimal physiological conditions for plant metabolism.
- Humidity Management: Air movement aids in controlling humidity levels around plants, which is essential for preventing fungal diseases and ensuring efficient transpiration rates.
Nutrient Uptake and Stress Resistance
- Nutrient Uptake: Healthy transpiration rates driven by adequate air movement help facilitate nutrient uptake through the roots. This is particularly important for plants in semi-closed systems where water and nutrient delivery can be challenging.
- Stress Resistance: Improved air circulation can enhance plants’ resilience to environmental stresses such as heat and drought by maintaining better leaf temperatures and promoting more efficient water use.
CO2 Concentration Management
- Carbon Dioxide Levels: Maintaining higher CO2 concentrations inside plant canopies can enhance photosynthetic efficiency. Air movement helps distribute CO2 evenly, reducing pockets of low concentration that can inhibit photosynthesis.
- Environmental Control: Effective air movement allows for better control of environmental variables, which is crucial in regulated growth conditions, leading to increased yields and healthier plants.
Practical Applications in Agriculture
- Design of Growing Spaces: Understanding the effects of air movement can inform the design of greenhouses, plant factories, and urban agriculture systems. Incorporating fans or ventilation systems can optimize air circulation, improving plant growth rates.
- Tailored Strategies: Different plant species may require specific air movement strategies for optimal growth. Research can help identify the best practices for varying crops to maximize their productivity in controlled environments.
Future Research Directions
- Continued Study of Microclimates: Future research should focus on understanding how microclimates within canopies are affected by air movement and how this can be leveraged to optimize growth conditions.
- Integration of Technology: Advances in technology, such as sensors and automation, can help manage air movement and other environmental factors in real-time, leading to more efficient and productive agricultural practices.
Conclusion
Effective management of air movement is crucial for enhancing gas exchange, regulating temperature and humidity, and improving nutrient uptake. By understanding and optimizing these factors, growers can promote healthy plant growth and maximize productivity, especially in controlled environments. Continued research and technological advancements will further refine these practices, leading to sustainable agricultural systems.
Air Current Effects on Plant Processes
Key Concepts
- Gas Exchange Mechanism:
- Plants exchange carbon dioxide (CO₂) and water vapor with the atmosphere, primarily regulated by:
- Stomatal Resistance: Control over gas diffusion into and out of leaf stomata.
- Boundary Layer Resistance: Resistance at the leaf surface affecting gas exchange efficiency.
- Plants exchange carbon dioxide (CO₂) and water vapor with the atmosphere, primarily regulated by:
- Environmental Influences:
- Various environmental factors affect photosynthesis and transpiration through stomatal aperture, including:
- Air Temperature
- Humidity
- Light Intensity
- Soil Conditions
- Various environmental factors affect photosynthesis and transpiration through stomatal aperture, including:
Effects of Air Current Speed
- Air Movement Impact:
- Air current speeds below 1 m/s significantly influence net photosynthetic rates (Pn) and transpiration rates (Tr).
- As air current speed increases from 0.01 to 0.3 m/s:
- Pn and Tr rates can double.
- Above 0.4 m/s, these rates become almost constant.
- Canopy vs. Single Leaf:
- Air movement has a more pronounced effect on plant canopies compared to single leaves due to:
- Greater restrictions in air movement within the canopy.
- Forced air movement is essential for enhancing gas exchange in plant canopies.
- Air movement has a more pronounced effect on plant canopies compared to single leaves due to:
- Boundary Layer Dynamics:
- The leaf boundary layer is thinner at higher air current speeds, facilitating better gas and heat transfer.
- Increased air current speeds lead to a:
- Decrease in leaf boundary layer resistance, improving gas exchange efficiency.
Photosynthesis and Transpiration Rates
- Rate Relationships:
- Both Pn and Tr rates increase significantly with rising air current speeds:
- Tr shows a greater increase compared to Pn as speeds rise.
- At an air current speed of 0.9 m/s, Pn is 1.2 times and Tr is 1.3 times higher than at 0.1 m/s.
- Both Pn and Tr rates increase significantly with rising air current speeds:
- Influence of Plant Canopy:
- Within a plant canopy, air current speeds can drop to 30% of those above it, necessitating controlled air movement for effective gas exchange.
- Canopy height and leaf area index (LAI) significantly affect the photosynthetic rates, with higher LAIs showing enhanced gas exchange at lower air current speeds.
Temperature Dynamics
- Effect of Air Movement on Temperature:
- Higher air current speeds lead to:
- Decreased leaf temperatures due to increased transpiration and latent heat transfer.
- Specific temperature reductions noted for plant organs include:
- Leaves: 14.1°C
- Petals: 12.8°C
- Stigmas: 11.9°C
- Anthers: 13.1°C
- Higher air current speeds lead to:
- Influence of Relative Humidity:
- Lower relative humidity can lead to increased leaf temperatures due to:
- Stomatal closure, which reduces transpiration rates.
- Lower relative humidity can lead to increased leaf temperatures due to:
Environmental Variability Inside Canopies
- Spatial Variation of Environmental Factors:
- Restricted air movement within plant canopies can lead to spatial variations in:
- Air Temperature
- Water Vapor Pressure
- CO₂ Concentration
- These variations must be monitored for effective crop production.
- Restricted air movement within plant canopies can lead to spatial variations in:
Conclusion
- Importance of Air Movement:
- Effective control of air movement is vital for:
- Enhancing gas exchange between plants and the surrounding atmosphere.
- Promoting optimal plant growth and development.
- Maintaining adequate air currents helps ensure uniform environmental conditions within the plant canopy.
- Effective control of air movement is vital for:
This summary provides a structured overview of the chapter’s content, highlighting the critical relationships between air movement, photosynthesis, transpiration, and temperature dynamics within plant canopies. Let me know if you’d like more specific details or explanations!
Table 25.2 presents data on how prior knowledge about Plant Factory with Artificial Lighting (PFALs) influences consumer perceptions. It compares consumer responses based on whether they had prior knowledge of PFALs or not, and evaluates different images or attitudes regarding PFAL-grown vegetables.
Key Findings:
- Vegetables Grown Using Artificial Light:
- Consumers with prior knowledge were significantly more likely to consider these vegetables “safe and reliable” (72 vs. 25) and provided a “stable supply” (57 vs. 19).
- Those without knowledge expressed more anxiety about the nutritional value (31 vs. 37) and taste (23 vs. 15) of these vegetables, with a statistically significant difference (p < 0.05 and p < 0.01, respectively).
- Vegetables Grown Hydroponically:
- Consumers with knowledge considered them “safe and reliable” (68 vs. 15) and provided a “stable supply” (36 vs. 6). There was also a slight positive difference in perception of freshness and taste (35 vs. 22).
- However, there was no significant difference regarding anxiety about nutritional value between the two groups (p > 0.1).
- Plant Factory (General):
- The perception of “safe and reliable” was not significantly affected by prior knowledge.
- However, knowledge positively influenced views on “large-scale mass production” (38 vs. 23) and “stable supply” (44 vs. 7).
Conclusion:
Prior knowledge about PFALs positively impacts consumers’ perceptions, particularly about safety, reliability, and the stability of the supply of vegetables produced in these systems. However, concerns about nutritional value persist, especially for hydroponically grown vegetables, suggesting a need for better communication regarding these aspects.
Recommendations:
Marketers should focus on educating consumers about the safety, quality, and production methods of PFAL-grown vegetables to address any concerns, particularly about nutrition and taste. This can be achieved through mass media, product packaging, and interactive consumer experiences like seminars and tastings.
About Us
Welcome to Agriculture Novel, your go-to source for in-depth information and insights into the world of agriculture, hydroponics, and sustainable farming. Our mission is to educate, inspire, and empower a new generation of farmers, hobbyists, and eco-conscious enthusiasts. Whether you’re interested in traditional farming practices or modern innovations, we aim to provide comprehensive guides, expert tips, and the latest updates in agriculture and urban farming.
At Agriculture Novel, we believe in the power of knowledge to transform the way we grow, sustain, and nourish our world. Explore our articles on topics like Fruit Growing Guide, Hydroponics, Plant Deficiency Guide, and more.
Thank you for joining us on this journey towards a greener, more sustainable future!
About Agronique Horizon
At Agronique Horizon, we specialize in delivering comprehensive digital marketing and web development solutions tailored for the agriculture and hydroponics industries. From custom website design and app development to social media management, we provide end-to-end support for brands aiming to make a meaningful impact. Our team also offers innovative solutions for the real estate sector, bringing precision and visibility to your projects. Learn more about our services here and discover how we can elevate your digital presence
