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Prickly Pear Cactus - DesertUSA

In 1881, he observed the movement of bacteria towards the chloroplasts in a strand of “” algae. Engelmann hypothesized that the bacteria were moving in response to oxygen generated by the photosynthetically active chloroplasts in the algae. This was one of the first documented observations of positive aerotaxis in bacteria. In 1882, he performed his famous action spectrum experiment using a device designed and built by . The modified microscope had a prism which could produce a microscopic spectrum on a microscope slide. The device could also distinguish and measure different wavelengths of light making it a “micro-spectroscope.” Engelmann used this device to illuminate a strand of (not Spirogyra) with light from the , exposing different sections to different wavelengths (or colors of light). He added the oxygen seeking bacteria B. termo to this setup and noted where they accumulated (Note: Four years later, Hauser concluded that B. termo had been mislabeled and was not one, but three species of bacteria of the genus Proteus ). Their clumping allowed him to see which regions had the highest concentration of oxygen. He concluded that the most photosynthetically active regions will have the highest concentrations of bacteria. The bacteria accumulated in the regions of red and blue light, showing that these wavelengths of light generated the most photosynthetic activity. However, his experiment was somewhat flawed because he used the sun as his lightsource. He failed to account for the fact that the sun does not emit all visible wavelengths of light at the same intensity. However, further analysis of plant pigments proved that his results were valid. A year later Engelmann discovered that utilise light in the same way.

Engelmann performed three significant experiments involving photosynthesis:

Picea engelmannii was studied over its natural elevational range in SE Wyoming. Low photosynthetic rates measured at constant temperature, irradiance and vapor pressure deficit were highly correlated with low minimum (night) air and soil temperature, but at different times during the early summer growth period. Substantial and irreversible reductions in photosynthesis occurred after exposure to night air temperatures of -4 and -5oC that occurred through mid-June. After middle to late June, decreased photosynthetic rates were correlated with low soil temperature. Subfreezing air temperature followed by an extended period of low soil temperature were the primary limitations to photosynthesis in early summer. -from Authors

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N2 - Picea engelmannii was studied over its natural elevational range in SE Wyoming. Low photosynthetic rates measured at constant temperature, irradiance and vapor pressure deficit were highly correlated with low minimum (night) air and soil temperature, but at different times during the early summer growth period. Substantial and irreversible reductions in photosynthesis occurred after exposure to night air temperatures of -4 and -5oC that occurred through mid-June. After middle to late June, decreased photosynthetic rates were correlated with low soil temperature. Subfreezing air temperature followed by an extended period of low soil temperature were the primary limitations to photosynthesis in early summer. -from Authors

AB - Picea engelmannii was studied over its natural elevational range in SE Wyoming. Low photosynthetic rates measured at constant temperature, irradiance and vapor pressure deficit were highly correlated with low minimum (night) air and soil temperature, but at different times during the early summer growth period. Substantial and irreversible reductions in photosynthesis occurred after exposure to night air temperatures of -4 and -5oC that occurred through mid-June. After middle to late June, decreased photosynthetic rates were correlated with low soil temperature. Subfreezing air temperature followed by an extended period of low soil temperature were the primary limitations to photosynthesis in early summer. -from Authors

Theodor Wilhelm Engelmann - The Full Wiki

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