Institute of Physical Biology

Lemna test (ISO/DIS 20079, ASTM 1992, OECD d.g.221/2002)

The duckweed species Lemna minor is used as a model organism for higher aquatic plants. Duckweed can be damaged by water or soil constituents and effluents. Inhibition of growth is calculated after 7 days from the observation parameters (frond number, frond area, chlorophyll, dry weight) by a number of defined calculation methods.

Acute test with bioluminescent bacteria Vibrio fischeri (ISO 11348, DIN 38412)
Water, sediment and soil samples are tested for toxicity using bioluminescent bacteria Vibrio fischeri. Marine bioluminescent bacteria like V. fischeri emit light naturally when they are in optimal environment. If harmful substances are present, their light emission is inhibited due to the influence on cellular metabolism. The degree of light inhibition is proportional to sample toxicity. The test consists of a geometric series of at least seven concentrations and toxicity is measured 30 minutes after exposure.

Monitoring of photosynthetic activity and plant stress

Photosynthetic activity and plant stress are measured with the pulse-modulated chlorophyll fluorescence method (OS5-FL Modulated Fluorometer, OptiSciences). The portable fluorometer enables measurement of chlorophyll fluorescence in daylight, regardless of light intensity and spectrum. The device can be used in field measurements for stress determination (photoinhibition, cold, heat, nutrients deprivation, etc.) and tolerance of plants to pollutants in soil, air and water. Additionally, bioavailability and specific action of herbicides can be measured.

Reflectometry in plants, chlorophyll concentration and spectrophotometric measurements of environmental samples is performed using a portable spectrophotometer (USB2000 Miniature Fiber Optic Spectrometer in USB-ISS-VIS snap-on cuvette holder and visible light source, Ocean Optics).

Mapping of vegetation indices in ecoremediation systems

Vegetation indices are spectral transformations of two or more bandwidths of reflected light spectrum from vegetation surface. They provide space-time information on photosynthetic activity, type and morphology of plant ecosystem, which enables seasonal, annual or longer-period monitoring of physiological, structural, phenological and biophysical parameters. Plants strongly absorb red wavelengths (photosynthesis) and strongly disperse near-infrared light due to scattering on water-air boundary in cell walls of spongy mesophyll tissue. Higher reflectivity in red spectrum is a consequence of lower photosynthetic activity, while lower reflectivity in near-infrared indicates water stress. Vegetation indices are normalised quotients of both reflectivities and represent overall plant stress.

The figure represents vegetation index mapping of a constructed wetland. Higher index values (green) represent better condition of vegetation, brown and blue are mineral surface.