Plant stress measurement

Plant stress measurement is the quantification of environmental effects on plant health. When plants are subjected to less than ideal growing conditions, they are considered to be under stress. Stress factors can affect growth, survival and crop yields. Plant stress research looks at the response of plants to limitations and excesses of the main abiotic factors (light, temperature, water and nutrients), and of other stress factors that are important in particular situations (e.g. pests, pathogens, or pollutants). Plant stress measurement usually focuses on taking measurements from living plants. It can involve visual assessments of plant vitality, however, more recently the focus has moved to the use of instruments and protocols that reveal the response of particular processes within the plant (especially, photosynthesis, plant cell signalling and plant secondary metabolism)

Measurements can be made from living plants using specialised equipment. Among the most commonly used instruments are those that measure parameters related to photosynthesis (chlorophyll content, chlorophyll fluorescence, gas exchange) or water use (porometer, pressure bomb). In addition to these general purpose instruments, researchers often design or adapt other instruments tailored to the specific stress response they are studying.

Photosynthesis systems use infrared gas analyzers (IRGAS) for measuring photosynthesis. CO₂ concentration changes in leaf chambers are measured to provide carbon assimilation values for leaves or whole plants. Research has shown that the rate of photosynthesis is directly related to the amount of carbon assimilated by the plant. Measuring CO₂ in the air, before it enters the leaf chamber, and comparing it to air measured for CO₂ after it leaves the leaf chamber, provides this value using proven equations. These systems also use IRGAs, or solid state humidity sensors, for measuring H₂O changes in leaf chambers. This is done to measure leaf transpiration, and to correct CO₂ measurements. The light absorption spectrum for CO₂ and H₂O overlap somewhat, therefore, a correction is necessary for reliable CO₂ measuring results. The critical measurement for most plant stress measurements is designated by “A” or carbon assimilation rate. When a plant is under stress, less carbon is assimilated. CO₂ IRGAs are capable of measuring to approximately +/- 1 µmol or 1ppm of CO₂.

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