RSL at Scientifica'11
The Remote Sensing Laboratories participated in the Scientifica’11 exhibition, which was held from August 26th to 28th in Zurich, Switzerland. The exhibition itself was the first of its kind, having been jointly organised by the University of Zurich (UZH) and the 'Eidgenössische Technische Hochschule' (ETH) in Zurich. The dominant theme of Scientifica’11 was “energy”.
RSL’s contribution consisted of an exhibit and experiments devoted to the question “Do plants waste energy?”. Several approaches in remote sensing which exploit the electromagnetic spectrum, including optical and thermal wavelengths, permit a detailed monitoring of plant status (biochemistry) and functioning (photosynthesis).
Plants are occasionally exposed to harsh environmental conditions, e.g. high temperature, intensive illumination, or a deficit of water and nutrients. Since plants cannot move, they had to evolve complex mechanisms to adapt to such conditions allowing them to maintain their vital functions. Research has shown that plant photosynthesis is often rendered inefficient by the partial closure of leaf stomata, itself a protective reaction to environmental stressors such as limited water availability. Remote sensing approaches permit investigations of this dynamic component of plant photosynthesis at different scales (e.g. canopy or ecosystem); see Damm et al. 2010 or Joiner et al. 2011; Frankenberg et al. 2011.
RSL staff presented two experiments demonstrating photosynthesis in action. Good knowledge of plant photosynthetic activity is essential for understanding how they utilise the available resources required to grow (e.g. light or water) and how matter fluxes (e.g. carbon uptake or transpiration) are affected by plant photosynthesis:
• For the first experiment, leaves from a well irrigated (healthy) and a dry (stressed) basil plant were exposed to a heat source. A thermal camera recorded the experiment over a time frame of 4 hours. By measuring the thermal emission it was clear that the well-irrigated plant was able to maintain its initial temperature, while the temperature of the stressed plant steadily increased. This effect is related to the transpiration rate of the plant, which is, in turn, driven by stomata opening/closure. Since photosynthesis depends on gas exchange (CO2, H2O) between the leaf internal air spaces and the ambient air, stomatal conductance can be used as proxy for photosynthetic rates. Consequently, the higher temperature of the stressed basil plant indicates a lower photosynthetic rate compared with the well-irrigated plant. The experiment was shown to the public as one-minute long time-lapse video.
Upper values show the current average temperature in each rectangle,
lower values show the temperature difference from the beginning.
In addition to the time-lapse video, the thermal camera was also used in the exhibition to monitor a set of different plants in real time, indicating their unique thermal signatures under ambient conditions.
• The second experiment showed the leaf water and chlorophyll content of a parsley plant using an ASD Fieldspec field spectrometer, which captures the reflected electromagnetic radiation in the wavelength range of 350 to 2500nm. In this case, there was no live demonstration, because it was not feasible to cause the plant to lose water quickly enough for demonstration purposes. Instead, a pre-recorded video was shown of a plant submitted to dehydration stress in the laboratory: The plant's spectral signature changed its properties in the near-infrared range (indicating decreasing leaf water content), while its spectral features in the visible part of the light spectrum (indicating chlorophyll content) remained unchanged.
Thus, part of the complex process of plant photosynthesis was shown in a tangible way to the visitor: A plant may look perfectly healthy to the human eye (it appears green) but may in fact be partially dehydrated, which manifests itself through reduced plant photosynthesis.
Scientifica's goal of making science tangible to the broad public was certainly met: Over 15,000 visitors attended the entire exhibition and were encouraged to plunge feet-first into the fascinating world of science.