While gas-exchange photosynthesis systems are the gold standard for plant stress measurement, they also have limitations. While they can measure all types of plant stress in C3 and C4 plants, the cost of these systems is significantly higher than that of other instruments used for plant stress measurement. Furthermore, each sample must acclimate to the measuring chamber for about two minutes before measurement. However, field portable gas exchange systems can now operate for long periods, under battery power, and are light enough for field use. So, if you want the most sensitive instruments available, want to measure all types of plant stress, and have the budget available, gas exchange is the best choice. Prices for gas-exchange photosynthesis systems start above $20,000.00 and go up to more than $50,000.00
However, if measuring larger, more statistically significant plant populations is part of your experimental design, or a more affordable measuring solution makes more sense, other options are available. Measurements using a chlorophyll fluorometer or a chlorophyll content meter only take a few seconds per plant, and these instruments cost a small fraction of the cost of gas-exchange instruments. In addition, porometers, used in drought stress measurement, can take 30 to 90 seconds to make a measurement and are also more affordable.
These less expensive instruments also provide great results if used correctly and for the right plant stress type. Since chlorophyll fluorescence has been shown to correlate linearly to gas-exchange measurements in C4 plants and curvilinearly in C3 plants, and plant stress can generally be measured before the stress is visible in the plant, chlorophyll fluorescence is often the first choice.
However, there are limitations, and choosing the best chlorophyll fluorescence measuring protocol for the type of plant stress of interest is critically important. For example, Y(II), the light-adapted fast chlorophyll fluorescence protocol, is the best choice for measuring heat stress in C3 plants, but is often an inferior choice for most other types of plant stress. The reason is that it will detect heat stress in C3 plants at 35 °C or above, but results vary with actinic light intensity. So, one must compare results to samples illuminated at the same light level. Therefore, FV/FM is usually the preferred chlorophyll fluorescence measuring protocol because of its correlation to gas exchange, and it allows one to compare all samples at the same known dark-adapted state.
FV/FM works well with most types of plant stress in C4 plants and is the preferred protocol in C3 plants except for heat stress. Affordable, lightweight dark clips allow for measuring more statistically valid plant population sizes, and prices range from the low thousands to more than $10,000.00.
No chlorophyll fluorescence protocol works with nitrogen or sulfur plant stress, at usable levels, in either C4 or C3 plants. A chlorophyll content meter is the best choice for these stressors. Measurements take a few seconds, instruments are relatively inexpensive, and they measure visible changes in leaves. Protocols for nitrogen management, for many types of crops, are available in the literature.
For drought stress, porometers are a reliable, relatively inexpensive solution for most C3 plants. FV/FM will measure early drought stress in C4 plants, not C3 plants.
So, if you want to measure all types of plant stress at an affordable price, we suggest a combination of instruments, including our PSK system, which measures FV/FM and Y(II). It has affordable, lightweight dark clips for large plant populations and a Y(II) meter for heat stress measurements. For nitrogen and sulfur stress, we recommend our CCM-200plus system or MPM-100 system for broadleaf plants, and our CCM-300 for grasses or conifers. For drought stress, in C3 plants, we recommend a porometer.
<strong>Recommendations for plant stress measurement </strong>
<strong>FV/FM –</strong>
<strong>C4 plants:</strong>
Drought stress, Heat stress, Cold stress, Light stress, Waterlogging or Flooding Stress, Microplastic toxicity, Some types of Nutrient Stress, Over-Wintering Stress, CO2 Stress, Air Pollution Stress, Herbicide Stress, Pesticide Stress, Chemical Stress, pH Stress, Biotic Stress, Herbivory (Animal) Stress, Weed Stress, Radiation Stress, Wind Stress.
<strong>C3 plants</strong>
Cold stress, Light stress, Waterlogging or Flooding Stress, Microplastic toxicity, Some types of Nutrient Stress, Over-Wintering Stress, CO2 Stress, Air Pollution Stress, Herbicide Stress, Pesticide Stress, Chemical Stress, pH Stress, Biotic Stress, Herbivory (Animal) Stress, Weed Stress, Radiation Stress, Wind Stress.
<strong>Y(II) –</strong>
<strong>C4 plants</strong>
It will work with most types of plant stress, but values are light level dependent. Does not work with nitrogen and sulfur plant stress
<strong>C3 plants</strong>
Recommended for heat stress
It will work on the same types of plant stress as FV/FM, but is much better for heat stress. However, values are light level dependent. Does not work with nitrogen and sulfur plant stress
<strong>Chlorophyll content meters -</strong>
These systems are recommended for nutrient plant stress in both C3 and C4 plants, especially nitrogen and sulfur plant stress. They will only detect plant stress when it becomes visible on the leaf.
To measure all types of plant stress as quickly as possible, at the most affordable price, we recommend a <strong>chlorophyll fluorometer system</strong> that will measure FV/FM, and Y(II), a <strong>chlorophyll meter</strong>, and an inexpensive porometer.
The <strong>PSK</strong> is our most affordable system that measures both FV/FM and Y(II). The <strong>CCM-200</strong> chlorophyll meter and <strong>MPM-100</strong> are designed for broadleaf plants, and our <strong>CCM-300</strong> works for small and difficult samples.
<strong>Porometer -</strong>
Meter “TM” makes a very affordable porometer.
References come from our Desktop Plant Stress Guide, which is available on our website. It contains worldwide references on measuring almost every type of plant stress.”