Hi, dear all: Measuring photosynthesis of plants in natural environments means make measurements under sometimes rapidly changing CO2 concentrations. As more plant you have to measure, as more changes in CO2 concentrations and also temperature and light intensity during the day occur. However you need a certain big number of plants, e.g. in field experiments with several variants and repetitions. How do you solve this problem?
First one, use several tools to measure at the same time many plants, no cheap solution.
Two, measure many plants at different times and correct or adjust each photo measurement using PAR, temperature, maybe leaf angle and possibly others as covariates; that adjust, let you compare treatments as if you were measured all the plants at the same time.
Dear Petra,
It will be easier to answer your question if you tell which type of instrumentation you have for measuring photosynthesis and the aim of your measurments. However, here are some thgoughts: If your use a differential or open gas exchange system, it is important to aviod rapid changes in the CO2 concentration as this will distrube your measurements. There are basically three ways of handling this: 1) Taking air into the instrument some meter above the vegation will decrease some of the most rapid variations in CO2 concentration; 2) Having a tank on the air inlet to stabilise the CO2 concentration over time; 3) Use bottled air or scrubb the air free from CO2 and thereafter add CO2 to the concentration you want, like in some commercial photosynthesis system (e.g. Licor 6400).
In summary, I recommend you first to stabilise your measurment conditions by different means as suggested above (could also be made for other variables) and if you would like to stude the effect of the variability in different environmental conditions, you can systematically manupulate these conditions in a step wise manner and one by one variable. It is time consuming but will give you much better results and understanding.
Thank you very much, dear Göran, for your helpful answer! We hope to by a Licor-6800 F this year. Nearly 20 years ago, I worked with a Licor-6200. However, I measured only wheat or barley plants (healthy or diseased with snow mold disease, net blotch disease or mildew) grown in Mitscherlich vessels in greenhouse or in climate chambers. The time span for from the first to the last plant was not as large, only 1 h for all measurements. We started (after calibration and scrub, of course) with the first vessel of variant A, than the first vessel of Variant B and so on. Thus we have no any troubles with diurnal changes of several physiological parameters. Now, we want to measure photosynthesis and so on in our field experiments BS4 and BS1 in our experimentation station Dahnsdorf (https://www.julius-kuehn.de/en/strategies-and-technology-assessment/fields-of-activity/long-term-field-trials/; https://www.julius-kuehn.de/en/field-and-greenhouse-services/experimental-sites-of-dahnsdorfkleinmachnow/). (BS 4 WG= winter barley, WR= winter rye, WW= winter wheat, Maize, Lupine each plot 25 m * 14m), the whole BS 4 nearly 150 m * 100m) another one is BS 1 with 400 * 150 m). This means it needs some time for all the measurements and I think it will be influenced by changes during the course of the day. I’m afraid that it will be even so, if I’ll measure only one culture, e. g. wheat. May be the expansive solution of Bernado “use several tools...” will be the best answer . However it isn’t a realistic one for us. We have been waiting two years get the money for the Licor 6800 F.
Hello again,
Your experiment looks very ambitious and exciting. Compared to the Licor 6200, both the Licor 6400 and Licor 6800 instruments have much better capacities to control the enviroment around the leaf during the measurements. The condition can be set both to track the ambient, or to a fixed levels independent on the ambient conditions. When doing many replicated measurements I recommend a standard protocol when all conditions are set to fixed level, e.g. light 1200 umol m-2 s-1, CO2 400 ppm, temperature 20 degree Celcius, humidity 60%. It works well in Licor 6400 and I sure it will work also in the Licor 6800 machine. There may still be some variation dure to diurnal influence of eg. stomatal openings, so avoid making all replicates of one species in the morining and another in the afternoon.
Good luck
Thanks for your useful recommendations and good wishes, best regards Petra
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