Chlorophyll content of leaves is an important characteristic of plant communities. It is related to the plant status, various plant and leaf developmental phases, the presence of soil fertilisers and chemicals, the climate, etc. Conventional methods to determine chlorophyll content require destructive sampling of leaves, extraction in 80% acetone or similar organic solvents and spectrophotometric measurement. A rapid and non-destructive estimate of chlorophyll content is possible using a recently marketed portable meter (SPAD-502, Minolta Corp.), based on the amount of light transmitted by the leaf in two wavelength regions (red and infra-red) in which the absorbance of chlorophyll is different. Earlier results indicated a linear and positive correlation between SPAD-502 readings and leaf chlorophyll content and showed the need for calibration for each plant species. The aim of this study is to evaluate the effect of various growing conditions on the SPAD-502 performances for Citrus leaves. The trial was carried out in 1995 on three-year-old plants of Citrus macrophylla, a Citrus rootstock. Twenty plants, grown in pots on a substrate of sand and peat (1:1 by volume), were kept in shaded conditions and watered regularly for two months. Successively plants were kept in a growing chamber and divided into two groups: one was well-watered and the other unwatered. In order to evaluate SPAD-502 characteristics and compare SPAD readings with colorimetric analysis, measurements were taken on 20 fully grown leaves of the same age from the shaded-grown plants using the chlorophyll meter and a portable colorimeter. Immediately following measurements, 20 disks per leaf (2.5 cm2 total area) were removed and macerated in 10 ml of 80% acetone. Chlorophyll suspensions were kept in the dark at 4 °C temperature. Absorbance of leaf extracts was determined on a spectrophotometer (Hitachi, mod. 100-60) at 647 and 664 nm, using the extinction coefficients proposed by Inskeep and Bloom in 1985. In the growing chamber after a month of acclimatisation, 4 homogeneous leaves per plant positioned in proximity to the tenth leaf beginning from the apex on different shoots were identified and marked for both well-watered and unwatered groups. Non-destructive colorimetric and chlorophyll meter measurements were taken daily on these samples for two weeks. In addition, xylematic pressure potential, chlorophyll concentration via spectrophotometer, colorimetric co-ordinates ans SPAD values were taken daily on another groups of leaves. For each experiment, area concentrations of total chlorophyll extracted (TCHL) were plotted against the respective values of SPAD-502 readings. From these correlations, the regression equations were developed. The results obtained from the experiment conducted over shaded-grown plants showed a good relationship between SPAD readings and TCHL concentrations. The slope and the intercept of the model were similar to previous results and R2 and the standard error of estimate (SEE) values were 0.92 and 4.6 microg cm-2 respectively. A significant correlation was also found between chromaticity co-ordinates and extractable chlorophyll with R2 ranged from 0.92 to 0.95 and SEE values were never greater than 5 microg cm-2. The growing chamber experiment results showed that the difference between the models developed for well-watered and unwatered plants were weakly significant (P<0.10). In both cases, the linear relationship was less good (R2 equal to 0.70 and 0.53 respectevely) in comparison with the results obtained from the experiment conducted over shaded-grown plants. A comparison between results from over shaded-grown and growing chamber experiments showed clear differences in regression models. Differences in instrument performance may be attributed to differences in leaf thickness, light scattering, leaf surface reflectivity and pigment distribution in the leaf. A combination of these morphological factors probably explains the reason why the relationship between SPAD and chlorophyll content values obtained for shaded grown Citrus plants is not valid for growing chamber plants. In conclusion, the portable chlorophyll meter is a useful instrument for non-destructive determination of TCHL in experiments where chlorophyll content has to be monitored over time. Our results indicate that growing conditions must be considered in model development. Because growing conditions show to influence the relationship between SPAD readings and TCHL, regression models must be determined for each experiment.
Sono state valutate le prestazioni di uno strumento (SPAD-502, Minolta Corp.) per la misura non distruttiva del contenuto in clorofilla di piante di agrumi sottoposte a diverse condizioni di allevamento e di rifornimento idrico. Per ciascuna prova sono stati analizzati i modelli di correlazione tra le indicazioni dello SPAD-502 e il contenuto in clorofilla totale per unità di superficie, determinato per via spettrofotometrica. In tutte le prove è stata riscontrata una correlazione significativa e positiva tra i valori dello SPAD-502 e il contenuto in clorofilla totale delle foglie. Le diverse condizioni di allevamento (ombraio e camera di crescita) hanno determinato variazioni significative, a parità di contenuto in clorofilla, dei valori indicati dallo SPAD-502. La differenza nella risposta dello strumento per diverse condizioni di rifornimento idrico è risultata debolmente significativa (P<0.10). Lo strumento ha mostrato di richiedere una calibrazione ad hoc non solo per le diverse specie e varietà ma anche per ciascuna condizione sperimentale che determini variazioni delle caratteristiche strutturali e morfologiche delle foglie, e quindi della loro densità ottica.
Uno strumento per la misura non distruttiva del contenuto in clorofilla: applicabilità degllo strumento agli agrumi
Duce P;Arca B;Ventura A;
1997
Abstract
Chlorophyll content of leaves is an important characteristic of plant communities. It is related to the plant status, various plant and leaf developmental phases, the presence of soil fertilisers and chemicals, the climate, etc. Conventional methods to determine chlorophyll content require destructive sampling of leaves, extraction in 80% acetone or similar organic solvents and spectrophotometric measurement. A rapid and non-destructive estimate of chlorophyll content is possible using a recently marketed portable meter (SPAD-502, Minolta Corp.), based on the amount of light transmitted by the leaf in two wavelength regions (red and infra-red) in which the absorbance of chlorophyll is different. Earlier results indicated a linear and positive correlation between SPAD-502 readings and leaf chlorophyll content and showed the need for calibration for each plant species. The aim of this study is to evaluate the effect of various growing conditions on the SPAD-502 performances for Citrus leaves. The trial was carried out in 1995 on three-year-old plants of Citrus macrophylla, a Citrus rootstock. Twenty plants, grown in pots on a substrate of sand and peat (1:1 by volume), were kept in shaded conditions and watered regularly for two months. Successively plants were kept in a growing chamber and divided into two groups: one was well-watered and the other unwatered. In order to evaluate SPAD-502 characteristics and compare SPAD readings with colorimetric analysis, measurements were taken on 20 fully grown leaves of the same age from the shaded-grown plants using the chlorophyll meter and a portable colorimeter. Immediately following measurements, 20 disks per leaf (2.5 cm2 total area) were removed and macerated in 10 ml of 80% acetone. Chlorophyll suspensions were kept in the dark at 4 °C temperature. Absorbance of leaf extracts was determined on a spectrophotometer (Hitachi, mod. 100-60) at 647 and 664 nm, using the extinction coefficients proposed by Inskeep and Bloom in 1985. In the growing chamber after a month of acclimatisation, 4 homogeneous leaves per plant positioned in proximity to the tenth leaf beginning from the apex on different shoots were identified and marked for both well-watered and unwatered groups. Non-destructive colorimetric and chlorophyll meter measurements were taken daily on these samples for two weeks. In addition, xylematic pressure potential, chlorophyll concentration via spectrophotometer, colorimetric co-ordinates ans SPAD values were taken daily on another groups of leaves. For each experiment, area concentrations of total chlorophyll extracted (TCHL) were plotted against the respective values of SPAD-502 readings. From these correlations, the regression equations were developed. The results obtained from the experiment conducted over shaded-grown plants showed a good relationship between SPAD readings and TCHL concentrations. The slope and the intercept of the model were similar to previous results and R2 and the standard error of estimate (SEE) values were 0.92 and 4.6 microg cm-2 respectively. A significant correlation was also found between chromaticity co-ordinates and extractable chlorophyll with R2 ranged from 0.92 to 0.95 and SEE values were never greater than 5 microg cm-2. The growing chamber experiment results showed that the difference between the models developed for well-watered and unwatered plants were weakly significant (P<0.10). In both cases, the linear relationship was less good (R2 equal to 0.70 and 0.53 respectevely) in comparison with the results obtained from the experiment conducted over shaded-grown plants. A comparison between results from over shaded-grown and growing chamber experiments showed clear differences in regression models. Differences in instrument performance may be attributed to differences in leaf thickness, light scattering, leaf surface reflectivity and pigment distribution in the leaf. A combination of these morphological factors probably explains the reason why the relationship between SPAD and chlorophyll content values obtained for shaded grown Citrus plants is not valid for growing chamber plants. In conclusion, the portable chlorophyll meter is a useful instrument for non-destructive determination of TCHL in experiments where chlorophyll content has to be monitored over time. Our results indicate that growing conditions must be considered in model development. Because growing conditions show to influence the relationship between SPAD readings and TCHL, regression models must be determined for each experiment.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
