Botany lab twelve photosynthesis

Vabira CO2 sensors module 

A test run of the rig with a plastic photosynthesis chamber yielded ever increasing levels of carbon dioxide on both the Neulog and the Vabira CO2 sensors. This was baffling as CO2 was climbing through 700 to 800 ppm. CO2 levels were rising inside the plastic photosynthesis chamber.

With both sensors in the glass photosynthesis chamber, a chamber which didn't arrive in time for the spring 2024 lab, and Alternanthera sessilis in a plastic (not peat) pot, CO2 levels fell as expected. 

I cannot fathom why the plastic chamber would make a difference. Or is the issue something about the peat pot. Thus far the Neulog sensor has not collapsed to 350 ppm as the sensor did last year. The Vabira, however is recording a greater drop in CO2.

The layout with power being supplied by the Wifi unit. The USB unit was feeding data to a laptop, but that data matched the data on the data logger screen. Manually recording data remains the easiest way to get the data into a table and graph. Google sheets is perfectly functional, although the botany class will be unfamiliar with this approach.

Datalogger screen 

In the laboratory an attempt will be made to get all of the sensors into place, but that may be challenging if the oxygen sensor is included. Still, that behaved well enough last year to be worth including. Perhaps the second chamber could be set up with the Vabira sensors only. 

Carbon dioxide data gathered using the glass chamber at the house three days ahead of the laboratory.

Plant transport was in an improvised box on Monday morning, 28 hours ahead of the. 

All equipment, plus the ethnobotany fruit salad supplies, also came up Monday morning. 

The Alternanthera sessilis was tucked into the germination trays.

Including the mini-pots used in the glass chamber.

To ensure all gear would be at ambient temperature, everything was put in a cabinet in A101. 

I went ahead with using both of the glass photosynthesis chambers, rigging the Vabira monitor on the south table. Both sensors are rigged through the smaller hole. One set of rubber corks didn't make it back into their chamber. They are in the Neulog box.

The Vabira was set up first to allow standardization to 428 ppm of CO2.

The other chamber was set up on the north table by the sink. The sink provided a place to rest the sensor panel.The students noted the order in the picture on the box and decided that was right order. The oxygen sensor was set up with the DO solution which is probably deionized water. An oxygen sensor that doesn't need DO would be useful going forward.

The layout canbe seen above. This image was captured at 13:03

As can be seen above, data gathering started at 11:52 for the Neulog rig, 11:59 for the Vabira (the Vabira takes time to standardize ).

Inside the classroom the Vabira rig experienced increasing CO2. The chamber was at 30 Celsius with a relative humidity of 79% and a vapor pressure differential of 0.89.

An extension cord was used to move the rig outside and CO2 fell precipitously while temperatures in the chamber soared.

Msyoleen and Marstella photo- record data outside.

The outdoor photosynthesis chamber. By 12:37 the chamber would reach 39 Celsius, well above the RuBisCo oxygenization temperature. The relative humidity inside was 81% with a vapor pressure differential of 1.33. The VPD would rise to around 1.58 and the chamber temperature would peak at 41 Celsius before being brought inside. 

Days collection on the Neulog oxygen sensor continued to 14:23. The CO2 sensor fell steadily until 400 ppm and then the sensor crashed to 350 ppm. The Vabira behaved in a similar way: falling to 400 and then remaining at 400 ppm.

The Neulog sensor data fell linearily for 42 minutes and then at 400 ppm the sensor jumped to 350 ppm, the same behavior as seen a year ago, behavior that led to the acquisition of the Vabira sensor. 

While the Neulog oxygen sensor data looked linear for the first 42 minutes, further data collection suggested a logarithmic relationship.

The Vabira sensor had behaved well at home, but at home the plant was lit by a 200 Watt LED lamp. That lamp was on the north table this term. For the first 36 minutes the chamber was in the classroom and CO2 levels rose. The plant was respiring but not photosynthesizing. At 36 minutes an extension cord was obtained and the chamber was moved into the sun. Over the next ten minutes the CO2 fell steadily to 400 ppm and then froze at that value. The inside of the chamber was climbing through 40 Celsius and that my have had an impact. An indoor LED lamp is clearly needed. Alternanthera sessilis is a sun-loving plant. Inside the classroom the plant was essentially in deep shade, not an environment in which this plant thrives. Outside in the sun the CO2 levels fell, at least up to a point. Why the value remained at 400 is unclear, but sensor had displayed the same behavior at the house. Perhaps the sensor range minimum is 400 ppm, but that seems to be a high bottom given that in a chamber plants can drop the carbon dioxide significantly. 

If this is run in 2026 the recommendation is to have two desk lamps with 200W daylight balanced bulbs to drive photosynthesis. Whether the plant should be Centella asiatica or Alternanthera sessilis is a tough call. The spinach will be used again during the chromatography lab which is a plus for the Alternanthera sessilis.