Original paper Environ. Control in Biol. 24(1), 21-26, 1986

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1 Original paper Environ. Control in Biol. 24(1), 21-26, 1986 Remote Sensing of Chlorophyll Content of Leaf (I) Effective Spectral Reflection Characteristics of Leaf for the Evaluation of Chlorophyll Content in Leaves of Dicotyledons Masatoshi AOKI* t, Kazutoshi YABUKI*, Tsumugu ToTsuKA**, õ õ and Minoru NisrnDA*, õ õ õ *College of Agriculture, University of Osaka Prefecture, Sakai 591, Japan **Division of Environmental Biology, The National Institute for Environmental Studies, Yatabe, Ibaraki 305, Japan (Received February 25, 1986) The effective characteristics of spectral reflectivity for evaluating chlorophyll con tent on a leaf areal basis were investigated in eight species of dicotyledonous trees and in sweet potato. Using regression equation between chlorophyll content and re flectivity ratio of rni'/rg', where rnl' and rg' are the spectral reflectivity at 800 nm and 550 nm, respectively, the chlorophyll content of the leaf was estimated in May to December. The obtained value showed the standard error of about 5ƒÊg Ecm-2, which is about 10% of the mean chlorophyll content of all leaves examined (sample size: 147), irrespective of species and seasons. The correlation equation for the esti mation was different from that for monocotyledonous plants reported previously. INTRODUCTION Chlorophyll content may be an important index of physiological activity of leaf. It is known that chlorophyll content of leaf decreases when the nutrient supply from soil is not enough and when leaves are injured by air and/or soil pollutions.1-3) It is very useful and convenient if such decreases can be evaluated by remote sensing technique without destroying leaf samples.3) Aoki et al.4) reported that the chlorophyll content on a leaf areal basis in Cinnamomum camphora, Nerium indicum and Viburnum awabuki could be determined by the use of reflectivity ratios, such as rni L/rG L and rni L/rR L, where rni L, rr L and rg L were the spectral reflectivity at 800, 630 and 550 nm, respectively. They also showed that the estimation error was about 100 of the chlorophyll content of healthy leaves, which was caused mainly by the thickness of leaves, and that the variation of leaf water content brought about little error when leaf water deficit was not so severe. Inada5' also reported almost the same õ Present address: Faculty of Agriculture, Yamaguchi University, Yamaguchi 753, Japan. õ õ Present address: Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu 183, Japan. õ õ õ Present address : Atsugi Technical Developmental Center, Asia Air Survey Co., Ltd., Onsui, Atsugi, Kanagawa 243, Japan. Vol. 24, No. 1 (1986) (21) 21

2 results in rice, wheat and barley, and Omasa et a1.6) in sunflower. The aim of the present paper is to clarify the most effective characteristics of spectral reflectivity for estimating the chlorophyll content on a leaf areal basis of various dicotyledonous species in different seasons. MATERIALS AND METHODS Species of plants tested were selected from three categories, i.e., the evergreen tree, the deciduous tree and the herbaceous plant belonging to dicotyledonous plant. As evergreen trees, Cinnamomum camphora (camphor tree), Viburnum awabuki (Japanese viburnum), Nerium indicum (sweet-scented oleander), Quercus phillyraeoides (Japanese holly oak) and Ligustrum japonicum (Japanese privet) were selected. As deciduous trees, Populus nigra (black poplar), Platanus orientalis (oriental plane tree) and Zelkova serrata (sawleaf zelkova) were chosen, and sweet potato was chosen as a herbaceous plant. The spectral reflectivity of leaves was measured as the wavelengths of 450, 550, 600, 630, 680 and 800 nm using Cary 17DX Spectrophotometer (Varian Co., Ltd., U.S.A.), and the obtained spectral reflectivities in percentage were expressed as rb L, rg L, r Y L, rr L, rfr L and rni L, respectively. The procedure of measurement was the same as reported bef ore.4) Total 42 kinds of reflection characteristics including the above mentioned six kinds of spectral reflectivities, the reciprocals of them and the ratios between two reflectivities in all combinations among them were chosen as an independent variable. Immediately after measuring the reflection spectrum of a leaf, ten disks of area 1 cm2 were punched out from the leaf and homogenized. Then the chlorophyll content was measured by the method reported by Smith and Benitez.7) The content of chlorophyll (a+b) was expressed as Đ g cm-2. The measurements were repeated in late May, early July, late August and late December 1981 to investigate the seasonal changes in the reflectivity. The sample size of measurements in each month is shown in Table 1. Additional measurements were made for 25 samples of leaves in Cinnamomum, 25 samples in Viburnum and 20 samples in Nerium in August Table 1 Sample sizes of measurements in each month. 22 (22) Environ. Control in Biol.

3 RESULTS For Viburnum in August, reflection characteristics such as rnl L/rG L, rni L/r Y L, rnl L/rR L, rb L/rG L, rb L/rY L, rb L/rR L, rg L and 1/rG L showed very high correlation to chlorophyll content with correlation coefficient (r) of above 0.8, although the other 34 reflection characteristics showed only poor correlation. Figure 1 shows the relation between reflectivity ratio of rni L/rG L and chlorophyll content of leaves in seven species examined in December The relation between reflectivity ratio rni L/rG L and chlorophyll content showed the highest correlation (r=0.98) for seven species of plant (sample size, n=35) in December (Fig. 1). There was a little difference in the relation among species. Table 2 shows the list of correlation coefficient between several kinds of reflection characteristics and chlorophyll content for Cinnamomum, Nerium and Viburnum in July using leaves. The numerals in Table 2 show that the reflectivity ratios rni L/rB L and Fig. 1 Relation between reflectivity ratio rni'/rg' and chlorophyll content of leaves in 7 species examined in December Symbols in the figure show the species as follows:, Nerium;, Cinnamomum; ~, Viburnum; +, Quercus; œ Ligustrum; A, Populus:, sweet potato. Table 2 Correlation coefficients in the relation between characteristics of spectral reflectivity and chlorophyll content of leaves in dicotyledonous species. rb L, rg L, r Y L, rr L, rfr L and rni L are the spectral reflectivity at 450, 550, 600, 630, 680 and 800 nm, respectively. n is the sample size. * Cinnamomum, Viburnum, Nerium, Quercus, Populus, Platanus, Zelkova and sweet potato (see Table 1), measured in August ** The eight species above mentioned and Ligustrum were measured (see Table 1). Vol. 24, No. 1 (1986) (23) 23

4 rni L/rFR Lcorrelated poorly (r= ) with chlorophyll content, while other reflection characteristics showed high correlation (r>0.8). The correlation coefficient (r) for 1/rG Lwas also large (r= ), but the linearity was not so better as for rni L/rG Land rni L/rY L. The variation of r for rni L/rG Lamong species was less than those for rni L/r Y Land rni L/rR L(Fig. 2). This result is almost the same as that of Inada5) for leaves of rice, wheat and barley, and similar to that of Omasa et al.6) for leaves of sunflower, although the correlation equation between reflectivity ratio and chlorophyll content is different from that of Inada.5) The correlation coefficient for rni L/rG Lobtained by 40 samples in eight species in August (r=0.95) showed similar value to that obtained in each species of Ginnamomum (r=0.98), Nerium (r=0.94) and Viburnum (r=0.95). Figure 3 shows the seasonal changes of regression line between rni L/rG L and chlorophyll content examined in 7-8 species (4-5 leaves in each species; n= 32-40; see Table 1). The regression lines in August and December when the leaves matured, showed slightly steep slope than those in May and July when the leaves were still younger or unmatured. However, the calculated correlation coefficient of rni L/rG Lexamined for 147 samples including data obtained by 9 species in different months was 0.95, which was the largest among all the re- Fig. 2 Correlation coefficients between reflectivity ratio and chlorophyll content of leaf in different species. The abscissa shows the wavelength (A) in the spectral reflectivity ratio, rni'/rĎ., Nerium;, Cinnamomum; ~, Viburunum;, 8 species*;, 9 species** (*, **: see Table 2). Fig. 3 Seasonal changes in the relationship between reflectivity ratio rni L/rG Land chlorophyll content of leaves in 7-8 species. Species tested are shown in Table 1. The regression line obtained for all samples (n=147) in 9 species is also shown with addition of those in different months. Y and X are the chlorophyll content in Đg cm-2 and rni L/rG L, respectively. The correlation coefficient (r) was 0.95 and the standard estimation error (se) was 5.0 cm (24) Environ. Control in Biol.

5 flection characteristics tested (see Table 2). Therefore, the reflectivity ratio rni L/rG Lseems to be the most useful reflection characteristics for evaluating chlorophyll content of leaves in any plant species tested. The following correlation equation between chlorophyll content (Y, pg. cm-2) and rni L/rG L(X) is applicable: Y=14.3X r=0.95 n=147 (1) se=5.0Đg. cm-2 The standard estimation error (se) was 5.0 pg. cm-2 chlorophyll, and the error was equivalent to about 10% of the mean chlorophyll content of all leaves examined. Equation (1) is different considerably with the correlation equation of Inada, 5) which is Y=23.2X DISCUSSION The structures of transverse section of lamina are much different among plant species tested. However, the chlorophyll content of leaves in different species of dicotyledonous plants could be evaluated accurately by one and the same correlation equation, irrespective of maturity of leaves. The correlation equation is not the same as that of Inada5) for leaves of rice, wheat and barley, as stated above, therefore the spectral reflection characteristics of leaf for dicotyledonous plant will be different from those for monocotyledonous plant. Further research should be necessary with respect to this point. The authors thank Dr. Kiyoshi Sugahara of The National Institute for Environmental Studies for his valuable suggestion concerning measurement of leaf reflection spectrum. The research was supported financially by gthe Special Research Project on Environmental Sciences; Basic Research on Analysis and Evaluation of Environmental Information by Remote Sensing (project leader: Prof., Dr. H. Toyota of Faculty of Engineering, University of Tokyo) hsupported by Grant in Aid for Scientific Research, the Ministry of Education, Science and Culture of Japan. REFERENCES 1) KNUDSON, L. L., T. W. TIBBITTS, and G. E. EDWARDS Measurement of ozone in jury by determination of leaf chlorophyll concentration. Plant Physiol. 60: ) SAKAKI, T., and N. KONDO Destruction of photosynthetic pigments in O3-fumigated spinach leaves. Res. Rep. Natl. Inst. Environ. Stud. 28: ) OMASA, K., and I. AIGA Evaluation of growth and physiological response of plants by image processing. Iden 31: ) AOKI, M., K. YABUKI, and T. TOTSUKA Remote sensing of the physiological func tions of plants by infrared color aerial photography (I), Relation between leaf reflectivity ratio, bi-band ratio and photosynthetic function of leaves in several woody plants. Studies on the effects of air pollutants on plants and mechanisms of phytotoxicity. Res. Rep. Natl. Inst. Environ. Stud. 11: Vol. 24, No. 1 (1986) (25) 25

6 5) INADA, K Spectral ratio of reflectance of estimating chlorophyll content of leaf. Jpn. J. Crop Sci. 54: ) OMASA, K., I. ALGA, and Y. HASHIMOTO Image instrumentation for evaluating the effects of air pollutants on plants. In gtechnological and Methodological Advances in Measurement, h Vol. 3 (Ed. by Striker, G., K. Havrilla, J. Solt, and T. Kemeny) , North Holland Publishing Co., Amsterdam. 7) SMITH, J. H. C., and A. BENITEZ Chlorophylls : Analysis in plant materials. In g Moderne Methoden der Pflanzenanalyse IV, h 142, Springer, Berlin.