Study on the Relationship among the Machilus Spectral Behavior and Light Intensity and Physiological Activity
Chinsu Lin
Assistant Professor, Department of Forestry
National Chiayi University
300 University Road, Chiayi (600)
Tel: (886)-5-2717476 Fax: (886)-5-2717467
Email: Chinsu@mail.ncyu.edu.tw
TAIWAN
Key Words
Spectral Behavior, Light Intensity, Photosynthetic Rate, Machilus zuihoensis var. zuihoensis, Remote Sensing
Abstract
Spectral reflectance characteristic of plants was determined by many factors, such as leaf structure, pigment concentration, canopy structure, biomass, sunlight, atmospheric conditions, and so on. Among which plant parameters should be the most important bases for vegetative detection or monitoring senses. In this paper, one hardwood species, Machilus zuihoensis var. zuihoensis was selected to be research material. Reflected hemisphere irradiance was measured from five samples. Photosynthetic rate and light intensity were also measured in the same time of irradiance measurement. This study focuses to understand the relationship among the spectral behavior and light intensity and physiological activity, especially the photosynthesis. Spectral behavior for different wavelength was also analyzed. The results are considered to be benefit for natural resources monitoring or detecting by remote sensing.
1. Introduction
Multi-spectral data have been applied in natural resources researches for more than 20 years whereas their classification accuracy, in general cases, are not very high enough to satisfy the needs for planning the environmental and natural resources management. Especially for the cases of range area, spectral characteristics of vegetation become more sophisticated due to the terrain effect and vegetative variations, such as changeable crown density and its structure, and mixed trees in stand in a pixel, and so on. The spectral band width limitation of multi-spectral data now is overcome. Hyperspectral data that have very narrowed spectral intervals and coded as 2 bytes digital number, give us the chance for understanding the spectral behavior of targets. Vegetation, the living organism, may reflect the incident radiation according to their physical and physiological properties and hence it is more difficult to know how is the interaction between the light and vegetation in view of reflectance or reflected radiance - the major senses of remote sensing.
The process of plant uptake carbon dioxide from the air and water from the soil to produce nutrients for its growing is so call as photosynthesis and is one of the most important physiological activities of plant. This process takes place only in the existence of light. The reflected radiance of a plant is therefore related with the light intensity and photosynthetic rate and the organization of plant canopy, a group of branches and leaves. To understanding the interaction between the light and leaf physiological process, a tree named as Machilus was selected for measuring the reflected radiance from its leaf. Light intensity and photosynthetic rate are also measured in the same time of radiance measurement. In the mean while the concentration of chlorophyll is also analyzed in the laboratory.
2. Materials and Methods
2.1 Materials and Instrument Description
Both Lauraceae and Fagaceae plants are the most important and dominant vegetation for the middle elevation mountainous area in Taiwan. Machilus zuihoensis var. zuihoensis, a Lauraceae plant is one of the governmental assigned reforestation plants and hence several two-year old potted Machilus seedlings were selected as the study material. A portable spectroradiometer, LI-1800, is applied to obtain spectral radiation data of the plant. Figure 1 shows the LI-1800 optional diagram. The cosine receptor is designed to collect the radiant flux according to the cosine of the incident angle based on the Lambert's cosine law and accept radiation from all angles of a hemisphere. Therefore the LI-1800 measures the irradiance (watts.m-2.nm-1) under such consideration and is the case applied in this study. It also can be set to recording data in radiance (watts. m-2.nm-1.sr-1).
Figure 1. Operational diagram of LI-1800 spectroradiometer (adopted from
LI-COR, 1989).
