Use the following information to answer the questions below: Below are two graph
ID: 190478 • Letter: U
Question
Use the following information to answer the questions below: Below are two graphs indicating light attenuation in water (at left), and in a forest (at right). Both indicate the amount of light available relative to the amount of light shining on the surface of the water (Light (% surface)) or forest canopy (Available Light (Ali). For the following questions you are two compare light attenuation in water as one dives downward to light attenuation in a forest as one rappels from the top of a canopy down toward the forest floor. Note that the top of the forest canopy is 26 meters above the ground, thus the data point at 24 m is two meters below the top of the canopy 3) Ground level in the forest would have same light quantity as which depth in the water? Light (% surface) 20 40 60 80 26 m 10 20 30 40 50 A 60 70 80 90 100 0.8-(Top of canopy) 0.6 24 m a 0.4 Ground level 22 m 20 m 0.2 14 m 1 2 4 Leaf area index (LAI)Explanation / Answer
Ans: Light attenuation is the total reduction in light energy with depth. sum of light scattering and absorption.
The amount of light at any depth is affected by the number of leaves above. Upon moving down through the canopy the number of leaves above increases so the amount of light decreases. However because leaves vary in size and shape, the number of leaves is not the best measurement of quantity. The quantity of leaves or foliage density is generally expressed as the leaf area. Because most leaves are flat the leaf area is the surface area of one or both sides of the lead. When the leaves are not flat, the entire surface area is sometimes measured. To quantify the changes in light environment with increasing area of leaves, we need to define the area of leaves per unit ground area (M2 leaf area/m2 ground area). This measure is the leaf area index (LAI). A lead area index of 3 (LAI=3) indicates a quantity of 3 m2 of leaf area over each 1 m2 of ground area. Leaves that are displayed at an angle rather than perpendicular to the Sun are also typical of arid tropical environments. In these hot and dry environments, angled leaves reduce light interception during midday, when temperatures and demand for water are at their highest.
The greater the leaf area index above any surface, the lower the quantity of light reaching that surface. As you move from the top of a canopy to the bottom, the cumulative leaf area and LAI increase. Correspondingly, light decreases. The general relationship between available light and lead area index is described by Beer's law. Besides the quantity of leaves the orientation of leaves on the plant influences the attenuation of light through the canopy. The angle at which a lead is oriented relative to the Sun changes the amount of light it absorbs. If a lead that is perpendicular to the Sub absorbs 1.0 unit of light energy (per unit leaf area/time), the same leaf displayed at a 60-degree angle to the Sun will absorb only 0.5 unit. The reason is that the same leaf area represents only half of the projected surface area and therefore intercepts only half as much light energy. Thus, leaf angle influences the vertical distribution of light through the canopy as well as the total amount of light absorbed and reflected. Although light decreases downward through the plant canopy, some direct sunlight does penetrate openings in the crown and reaches the ground as sunflecks. Sunflecks can account for 70-80% of solar energy reaching the ground in forest environments.
In contrast to aquatic environments where the absorption of solar radiation by the water itself is a distinct vertical gradient of light the dominant factor influencing the vertical gradient of light in terrestrial environments is the absorption and reflection of solar radiation by plants. The quantity and quality or the spectral composition of light that does penetrate the canopy of vegetation to reach the ground varies with both the quantity and orientation of the leaves. In Coastal and open water (murky vs. clear), depth, wavelength of light. Wavelengths of red light are attenuated rapidly and blue is attenuated less rapidly and can reach the greatest depth.