Refer these two papers, you may get some ideas

Dinghui Zou and Kunshan Gao (2009) Effects of elevated CO2 on the red seaweed Gracilaria lemaneiformis (Gigartinales, Rhodophyta) grown at different irradiance levels. Phycologia: November 2009, Vol. 48, No. 6, pp. 510-517.

TEMPERATURE RESPONSE OF PHOTOSYNTHETIC LIGHT- AND CARBON-USE

CHARACTERISTICS IN THE RED SEAWEED GRACILARIOPSIS LEMANEIFORMIS

(GRACILARIALES, RHODOPHYTA)

Dear Dungle.

in my opinion.it is good to measure DO. I wanna know  what kind of instrument was used for detecting DO in the culture. if you do you exp in the closed system (in bottle), it should not be difficult to check the absorption rate of NO3 and PO4. You can measure the different of nutrients concentrations between beginning and the end. it is the uptake by algae.   you can search many papers about this. I attached a paper by my classmate. hope it is help you.

Hi Dung,

First, to estimate CO2 assimilation from O2 evolution rates you might use Photosynthetic Quotients (PQ) values for Sargassum sp. or similar species from the bibliography. However, you should also take into account the environmental differences between these studies and yours. For example Rosenberg et al (1995)  gives a PQ value for Sargassum cymosum.

Secondly, in relation to nutrient uptake experiments, you can follow the nutrient concentration in your bottles by taking samples at fixed time intervals by the depletion method. I recently published an article where you can find many references about this subject (Sánchez de Pedro et al 2013, Phycologia).

I recommend you the review by Harrison and Hurd (2001) about the "nutrient physiology of seaweeds" and also the article by Pedersen (1994) where different methods of nutrient uptake experiments are compared.

I hope this can help you out

Kind regards

References

Harrison P.J. & Hurd C.L. 2001. Nutrient physiology of seaweeds: application of concepts to aquaculture. Cahiers De Biologie Marine 42: 71–82.

Pedersen M.F. 1994. Transient ammonium uptake in the macroalga Ulva lactuca (Chlorophyta): nature, regulation, and the consequences for choice of measuring technique. Journal of Phycology 30: 980–986.

Article Differential nutrient uptake by two segregated red algae in ...

Article Primary Production and Photosynthetic Quotients of Seaweeds ...

One of the problems (besides which PQ to use) you will face in designing such experiments with large, differentiated algae like Sargassum Sp. is the selection of the sample of tissue you incubate.  Different segments of the thalli will produce different patterns of specific productivity. If your intent is to characterize productivity at the level of the whole plant or sward, then you should incubate intact, whole plants. I tried this with a large Laminarian kelp and it worked well. Whatever the size of plant you incubate, you want to keep the ratio of tissue weight to water volume less than 0.4g fresh weight per litre of incubation volume, and the incubation period to less than 4h if you are to avoid serious experimental artifacts.

Hatcher BG 1977 An apparatus for measuring the photosynthesis and respiration of intact large marine algae and comparison of results with those from experiments with tissue segments. Marine Biology 43:381-385.

I would agree with everything Bruce has said. I would also add that you will need to know the PQ value if you want an accurate estimation. If you don't know the PQ, try searching in the literature for another Sargassum species, but the results will be slightly off. You could also try simultaneous measurements of pH and take bottle samples from before and after for total alkalinity or dissolved inorganic carbon. If you don't have the facilities to measure total alkalinity or DIC, then at least pH will give you an estimate of how much pH has changed relative to the oxygen consumption.

It is necessary to do c-fixation and nutrient absorption experiments separately. If you measure the  oxygen concentrations accurately, you will get reliable results for carbon fixation by conversion of oxygen produced into carbon fixed. Better to measure the chlorophyll-a also per unit biomass of algae.  Then you will be able to calculate carbon fixed per unit biomass. Conduct the experiment separately but in parallel, under same conditions with similar algal biomass measure the nutrient concentration  initially and after particular incubation period similar to carbon fixation.

Thank you all very much for recommended papers and suggestions. Those all information are helpful for my works alot. Thank you 

Dear Bruce Gordon Hatcher and Raquel Sánchez de Pedro

Actually, I found and read carefully the paper of Rosenberg et al (1995), I found that he recommend to use PQ value as 1, though there are some papers published that PQ value with wide range depend on the spatial distribution of seaweed species and different species. So, I would like to calculate the PQ value from my own experiments, but I could not, because when I referred some papers I found that the authors often describe briefly how to calculate to value and showed the final results in their papers. So, please give me information or related paper to calculate the PQ. Thank you and sorry for silly question because I've just started working in this topic.   

Dear Christopher Edward Cornwall

Thank you for suggestions. I've searched information of this topic for month but I just found some papers related to the topic. I agree PQ value is the value I have to get before I can calculate the amount of c fixation by seaweed. Now I am searching how to calculate PQ based on my experiments    

Dear Wanchun Guan

Thank you, I used the closed system and of course I have to measure nutrient in water of initial and final experiment, the period time is 1 and 2 h to measure simultaneously water samples at the light and dark bottles. I got some data to show that nutrients were depleted in light bottles and were produced in dark bottles. And in my experiment, I did to measure DO and nutrient in parallel, of course I have to avoid contamination of the water samples when measuring different parameters.  

Dear Dung,

my team also checked the uptake rate of nutrients of Sargassum horneri in the closed system. the uptake rate is dependented with light condition. the irradiance used in my experiment is decided by the incubated light condition.

Simply by the Winkler's method of titration or measure O2 content using polarography (Oxygen Electrode)

Dear Dung, I dont know whether my answer  now is relevant to you as it is already one year late.  Incubation of tissue bits/ entire thallus  in seawater see the following publications. Use the PQ of 1.25 to convert the oxygen to carbon equivalents.  For seagrasses I have used thick polythene bags  while I was working  at Minicoy Island of Laccadives.  

1. Kaladharan, P. & I.Davidraj , 1989.  Primary production of seagrass    Cymodocea serulata and its contribution to the productivity of Amini Atoll of Lakshadweep Islands.Indian J. mar. Sci.,18:215-216.

2. Kaladharan, P. & S.Kandan, 1997.  Primary productivity of seaweeds  in the lagoon of Minicoy atoll of   Laccadive Archipelago. Seaweed Res. Util.,19 (1 & 2): 25-28.

 3. Kaladharan, P., K.A. Navas &  S. Kandan. 1998.   Seagrass production in Minicoy   atoll of Lakshadweep archipelago.   Indian J. Fish., 45(1): 79-83.

 Wish you good luck.

Thank you so much for your answer and references. Best regards

To calculate CO2 sequestration from O2 liberation using the Gaarner&Gran "dark and light" bottles method, you will need to know the PQ value: PQ = +O2/ -CO2 and the best method to determine PQ is using the Warburg indirect manometric method. I recommend you to read my 1980 paper on this subject published in "Photosynthetica" 14(3)3370342

Thanks Rene

My pleasure. Did you read my paper? If you do not have access to it, send me your e-mail and I will send you a copy.

René

Thank you, I read this paper already and referred to my work.

Best

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https://fau.digital.flvc.org › fau:33673 › OBJ › view

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Radioactive tracers can also be used