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| Home > Publications database > Monitoring the evolution of plant photosynthetic performances using ground sun-induced fluorescence measurements |
| Conference Presentation (After Call) | FZJ-2015-03092 |
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2015
Abstract: Plants subjected to biotic or abiotic stress factors can respond with adjustments in their biochemical and physiological processes. These adjustments are often accompanied by changes in reflectance, transmittance, and absorbance at leaf and canopy level.This contribution aims to understand how optical signals linked to plant physiology changes after the application of two different chemical agents: an herbicide blocking the electron-transfer mechanisms in the photosynthetic apparatus (Chlortoluron) and an anti-transpirant chemical known to reduce plant transpiration (Vapor Gard) by sealing the stomata. The chemicals have been applied on 9 grass plots with different concentrations. Three plots have been kept not-treated and used as control. Canopy high resolution spectral measurements and CO2 fluxes have been collected daily on the same sampling area in each plot for the entire duration of the experiment to monitor the temporal evolution of the stress effects.Spectral measurements have been used to estimate the sun-induced chlorophyll fluorescence in both the red (SIF687) and far-red region (SIF760), the Photochemical Reflectance Index (PRI) linked to the xanthophyll-related heat dissipation and several traditional vegetation indices related to canopy greenness and chlorophyll concentration. SIF687 and SIF760 were estimated with spectral fitting methods spectrally modeling the radiance collected with very high resolution spectrometers in the oxygen absorption O2-A and O2-B bands.The applied treatments induced a variation of plant photosynthetic functioning modulated according to the level of herbicide concentration. Both SIF687 and SIF760 measured in Chlortoluron-treated grass plots were significantly higher than in the control plots. The highest dose caused fluorescence values to double in less than 3 hours while the reflectance signal at the same time was not affected confirming that the increase in fluorescence emission was only related to variations in the plant functional status not associated to changes in pigment content and composition. F687 and F760 values of treated plots decreased steeply in the following days. Fluorescence decline was accompanied by a decrease in chlorophyll content. Grass photosynthesis began to decline immediately after the herbicide application and continued in the following days. This result implies that fluorescence was negatively correlated to plant photosynthesis in an early phase of stress reaction and then the relation became positive in the following days. Thus the translation of fluorescence values to photosynthesis is not straightforward in this experiment. Lower doses affected fluorescence signal similarly but with a different temporal dynamic in both the initial rise and the recovery. Chlortoluron also caused an initial increase of PRI values followed by a gradual decline associated to the degradation of the pigment pool. The application of the anti-transpirant agent only slightly affected fluorescence emission and PRI probably because the photosynthetic system was not directly compromised.Sun-induced chlorophyll fluorescence allowed to monitor the temporal dynamics of plants’ functioning and recovery after the application of temporarily blocking photosynthesis agents. Further studies are ongoing to better understand the effects of stress on the fluorescence signal and the link to heat dissipation and photosynthesis.
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