I want to calculate the Redfield ratio for growth medium. I measured NO3 and PO4 content, if I divide the concentrations, will I get the Redfield ratio?
Deas Simrat,
The redfield ratio is the average stoichiometry of phytoplankton. Therefore it sets average relative requirements of these elements (C:N:P), the "fixed" values of 106:16:1. If you divide the nitrate and phosphate concentrations you will get the ratio of these compounds in your growth media. If calculated before the cultivation, it can tell you about effects of different supply ratios on your experiment, and after (assuming stationary conditons) it will tell you about the requirements of the cultivated species or assemblage under the experimental conditions. But be aware of other nitrogen forms that are preferentially used by some species or under certain conditions, as amonia and nitrite. So your NO3:PO4 may not reflect the actual comsumption or supply. Also, to evaluate gross consumption the right way is to use radiotracers as N15.
Hi Alexandre,
I am trying to get this ratio after cultivation. As any alteration in this ratio affect the species composition in natural environment and in my case it is a problem of contaminants that grow when N:P is below 10. So i need to measure N:P in cultivation medium to avoid growth of contaminants.
Would you recommend NO3/PO4 as a proxy for redfield ratio?
The ratio should be calculated molarity when comparing Redfield ratio! Redfield ratio is the global mean value of phytoplankton but the value deviate considerably depending on the species composition and nutritional status of living phytoplankton, and ambient nutrient concentration/ratio. Therefore, just comparison of the ratio measured in the culture and Redfield ratio tells almost nothing. What the important is the factors altering stoichiometry of phytoplankton and the relationship between nutrient supply and community composition. Make sense? P.S. Ammonia should be measured in addition to NO3+NO2.
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