An important potential use of the new PhotosynQ MultispeQ is for farmers to measure photosynthesis on crop plants and base management decisions on the results. We did a couple of mini studies at iFARM to demonstrate this potential. Dorn planted a new cover crop mix last fall with winter rye and Austrian winter pea. We measured some aspects of photosynthesis on individual Austrian winter pea leaves in three different fields with different densities of rye and pea.
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I am holding the MultispeQ with a single leaflet of Austrian winter pea in the measurement chamber and with my hands shielding the opening from the sun.
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Upper or leftmost: Chlorophyll content of Austrian winter pea leaflets in three fields. Lower or rightmost: Photosynthetic efficiency (Phi2) of Austrian winter pea leaflets in three fields. Each bar is the mean of nine measurements (3 leaflets on each of 3 plants). The error bars are probably +/- 1 standard error.
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It took less than 15 minutes to make the measurements in each field. As expected, there is not much difference among fields in winter pea photosynthesis. All of the pea plants looked very healthy.
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The case of the wilty red clover. A patch of stressed hay field surrounded by healthy vegetation where some new soil had been delivered earlier.
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We also focused our photosynthesis sleuthing on a mysterious patch of wilting hay field. We took measurements on individual leaflets of red clover inside of and surrounding the patch of stressed vegetation.
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Closeup view of the boundary between stressed and healthy hay field. Upper: RGB photo. Lower: NDVI image from Wratten 25A infrared plant health camera.
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Normal photos and NDVI images suggest that there is a dramatic difference in plant health between the grayish patch and the surrounding green hay field. We collected MultispeQ measurements on nine leaflets of red clover (Trifolium pratense) inside and outside the stressed patch. The first set of measurements was confusing, so we repeated the sampling. The second data set made a little more sense and revealed an interesting phenomenon.
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MultispeQ field measurements go much faster if one person drives the Android app on a mobile device (left) and another clamps the leaf into the MultispeQ chamber (right).
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Photosynthetic efficiency (Phi2) of red clover leaflets differed between plants inside and outside the stressed patch of hay field. There was much more variability within the stressed patch.
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As we were collecting measurements, we remarked that the sun had been behind a cloud for all of the samples of clover in the healthy vegetation, but when we started to measure the first stressed plant, the sun came out strongly. After four measurements of stressed clover leaflets, a cloud moved in front of the sun again.
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Light intensity (PAR) during each measurement and time of measurement of clover leaflets in healthy (green dots) and stressed (orange dots) hay field. The sun was shining brightly only for four measurements in the stressed vegetation.
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Photosynthetic efficiency (Phi2) and time of measurement for nine healthy (green dots) and 10 stressed (orange dots) red clover leaflets. The lowest photosynthetic efficiency measurements are the four measurements taken when the sun was shining.
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The changing sunlight seemed to add a variable that makes it difficult to conclude much about the relative photosynthetic health of these clover plants. For the measurements taken when the sun was behind a cloud, there is not very much difference between stressed and healthy clover plants, although that small difference could be important. A different sampling strategy and bigger sample sizes would have helped reveal the underlying pattern. Maybe some of the other measurements made by the MultispeQ (chlorophyll content, non-photochemical quenching, linear electron flow, proton motive force) could help solve the case. I need to learn more about what each of these measurements tells us about plant health. It would also be good to know which ones are more sensitive to changing ambient light conditions. I assume the wilting clover are drought stressed (probably due to thin soil over bedrock and lack of rain). Which MultispeQ measurements tell us the most about drought stress? There is much to learn.

Thanks to Mike, Dorn, and Ned for field assistance and photos.