Study on the Relationship among the Machilus Spectral Behavior and Light Intensity and Physiological Activity
In briefly,
leaf pigments absorb most of the incident blue
(
l £
500 nm) and red (600 nm
£
l < 700 nm) energy that are known as the
photon flux density for photosynthesis (Kramer and
Kozlowski, 1979). Significant RI Peak in the green
is of course results from the color of leaf. The
leaf RI increases dramatically in the infrared
region (700 nm
£ l ). One noticeable phenomenon of RI curves is that there are several valley happened in the infrared region. Dips in RI curve occur at 760, 820, 900, 914, 940, and 1100 nm is not appeared in the reflectance curve of healthy vegetation (Lillesand and Kiefer, 1992).
3.3 Relationship among the Leaf Reflected Irradiance and Light Intensity and Photosynthetic Rate
Theoretically the squared correlation coefficient (r
2) of any two variables is identical to the coefficient of determination (R
2) of a simple linear regression equation fitted by those two variables (Eq. 1). This study therefore applied the correlation analysis method to examine if the leaf-reflected irradiance of a particular wavelength is correlated with light intensity and photosynthetic rate. A Student's t test is then used to examine if the correlation coefficient of these two variables is statistically significant under 5% significance level. The results also could be the evidence of what will the leaf-reflected irradiance depend on the wavelength variation.
Figure 5. Relationship of the reflected irradiance and light intensity and that of the reflected irradiance and photosynthetic rate.
The correlation coefficient and its correspondingly significant probability of the leaf-reflected irradiance and light intensity (LUXcorr and LUXprob), and that ones of the leaf-reflected irradiance and photosynthetic rate (PNcorr and PNprob) for each wavebands are shown in figure 5. An interesting trend of these two correlation coefficient curves shows that a positive correlation exists in the visible area whereas a negative correlation exists in the infrared area. But the negative relationship should not be real for both case of light intensity and photosynthetic rate. Only the reflected irradiance in the range of 690-692 and 606-636 nm is significant correlated with light intensity and their correlation coefficient is about 0.90 and 0.85 respectively. While there are much of wavelength ranges (400-444, 500-532, 606-666, and 688-690 nm) whose reflected irradiance are significant correlated with photosynthetic rate and their correlation coefficients are correspondingly greater than 0.90.
4. Discussion
The study results showed that leaf-reflected irradiance is significantly correlated with photosynthetic rate in partial wavelength intervals of blue, green, and red bands; and is also significantly correlated with light intensity in a relatively narrow bandwidth of red band. They both have showed the 690 nm band is a common position where the correlation between the leaf-reflected irradiance and light intensity and photosynthetic rate are statistically significant. Since the 690 nm band is located at the edge of visible and infrared bands, it could maybe widely used for vegetation researches with remote sensing techniques.
Another important result of this study is that the light intensity is not linearly correlated with leaf-reflected irradiance. This maybe give us a hint of that leaf-reflected irradiance is somewhat independent with light intensity but it should be well examined by additional new measurement or experiment to test if it will be same for the case of leaf radiance or reflectance. In the future we will also focus on studies to understand if there is a nonlinear relationship exist between the light intensity and leaf-reflected irradiance.
5. References
- Kramer, P. J. and T. T.
Kozlowski. 1979. Physiology of Woody Plants. NY:
Academic Press. 811pp.
- LI-COR Inc. 1989.
LI-1800 Portable Spectroradiometer Instruction
Manual. Publication No. 8210-0030. Nebraska USA.
- LI-COR Inc. 1982.
Radiation Measurements and Instrumentation.
Publication No. 8208-LM. Nebraska USA.
- Lillesand T.M. and R.W. Kiefer. 1994. Remote Sensing and Image Interpretation. NY: John Wiley & Sons, USA.
