Hi Dung, usually we use expensive instruments such as LiCor, Ciras or ADC devices to measure the leaf gas exchange. If you can not find these instrument around you you can not measure directly photosynthesis... You may focus

(i) at the leaf level by measuring chlorophyll content in order to have an index of photosynthesis efficiency (see Lichtenhaler 1987), but chlorophyll content and carbon assimilation may be weakly correlated... you can also have an index through chlorophyll meter such as SPAD that is a quicker measure but necessitate to be calibrated for your species. Specific Leaf Area is also a trait often measured (see Wright 2004), dry mass is quite easy to obtain, for leaf area you can find very consistent relationship between length, width and area of som mangrove tree species leaves...

(ii) at the stand level by monitoring diameter increment with dendrometers band (UMS). In this last case, be carefull because sometimes variation in diameter may be caused by air humidity (see Stahl 2010)

Good luck for your research, do not hesitate to ask me some more questions and to communicate about your results. Carbon uptake by mangroves is an important topic in our context of climate change...

Article Seasonal variation in atmospheric relative humidity contribu...

Dear Dung,

Felix' answer addressed the most relevante aspects of you question. Let me just add that the Canadian manufacturer Qubit Systems sells basic infra-red gas analysers at significantly lower prices than the reference brands cited by Felix. Although there are designed primarily for teaching purposes they may provide a solution to your problem.

Best

I have a masters student starting to do some work on PS in mangroves. We are mainly using PAM machines. You can get a very basic PAM (they work just as well as the expensive ones) for about $2000. However, PAMs are black box machines and you need considerable expertise to use them properly. I have published several papers on PAM including PS studies on orchid, pineapples and water lilies.

Trying to measure PS by gas exchange in mangroves is particularly difficult because of the gas exchange of the mud they live in and the aerenchyma. Trying to measure PS using O2 electrodes using mangroves is very difficult and a special "leaf" O2 electrode is required.

There is a very old method of measuring photosynthesis using a thing called the Petterkoffer method which is based on CO2 absorption by NaOH. It can be made to work.

Hi Dung,

I would use a portable PAM fluorometer as Raymond Ritchie recommended below. It is relatively easy to use, nonintrusive and provide very good estimation of photosynthetic rates in plants. I have noticed that many institutions have one or more of them in their equipment.

Cheers.

My dear colleagues and friends

Thank you so so much for your very helpful answers, suggestions and comments. Hopefully I will find the best method among these. Thank you.

I guess you need to quantify net photosynthesis at stand scale. This is basically a growth analysis and once you collected the microclimate variables including radiation rainfall and salinity you can calibrate leaf area and shoot or trunk mass using a photocopier a pan an oven and a ribbon with a metric scale. Some 50 to 80 shoot with a variable number of leaves would provide leaf copies and dried stem mass. cut the copies along laf shapes and weight. Keep the copies in files. For every season measure trunk and shoot radial growth at labelled marks and estimate above mass and area by the previous calibration. RGR is the slope of log mass against time, and it is made by the ratio of net phosynthesis to mass area density. At last take aerial pictures and label the observation places. Probably there will be a gradient from seaashore to soft water.

No way to obtain it without IRGA´s or similar methods. LAI as such does not help, neither chlorophyll contents nor chlorophyll fluorescence studies (problem of dynamic photosynthesis in light-flecks). One could determine it indirectly as NET ASSIMILATION RATE = NAR from studies into biomass increment over time, but, since you most likely do not know the root/shoot ratios of the mangroves will face a large source of error here.

Well Dr Kuppers suggests to use irgas for mangrove 'forest' photosynthesis, but Dung put in evidence the lack of equipment. I will check again but there are 2 possible meanings of irgas: leaf chambers and microclimate profiling. Even in the case of both would like to know how to integrate them in situ. As far differences between NAR and photosynthesis I did follow humid forest protocols with minimal equipement and the is no reason to believe in differential night respiration rates unless it is the case.

I can add a cheap substitute for a leaf area machine. You take the leaves and scan them using a simple office scanner. You then print out the scans and weight the paper (A4) which has known area. You then cut out the images of the leaves and then weigh them. Do a regression of L x W of leaves vs Area so you can simply do length and width in field and calculate areas. Mangrove leaves of each species have a very standard shape and so it will work well. You can then work out the area of the leaves from simple field measurements.

I think trying to do IRGA in a mangrove swamp is severely impractical. PAM can be done using a Junior PAM and a tablet computer.

Dung wishes to obtain PHOTOSYNTHESIS RATES (=A), but does not give necessary background information such as "per leaf area" or per total "crown area", or "per day" or per "vegetation period" since this helps to modify experimental approaches. There is no way around to obtain A either by C-acquisition studies (drymatter increment) or via the help of IRGA-based gas exchange equipment (working in the atmosphere). Knowing (total canopy) leaf area is very important (as suggested by Ritchie via geometry approaches easily obtained, works always!)), but this itself does not provide any information on photosynthesis rates at all, but is an important scaling factor when scaling up from leaf to canopy.

Sorry, reliable information on A nowadays depends on gas exchange equipment. "Eddy correlation" faces many other problems....

Yes the idea is scaling mass and area as in several Brian Enquist lab issues. This would not deprecate Lange (and Ball at Canberra) gas exchange approach, but then there were quantum yield, basic leaf physiology and stomatal response questions left open in secretive plants. RGR is a compound expression of net photosynthesis fraction left by night respiration divided by carbon surface density. The portion going to different parts like trunks, shoots new leaves roots and reproduction is a matter of photocopier, ribbon, oven and scale and it is reasearch. Printer paper is stable for years. Eddy correlation in tidal boundaries could be a matter of large scale experimental stations. Chla fluorescence can easily find stress periods in daily courses as leaf chambers do but with less investements. I am much more interested now in erosion control under saline condition.

A common miss-understanding: Chlorophyll-fluorescence measurements (PAM) yield photosynthesis RATES only when the whole photosynthetic apparatus is in the (quasi-) steady state. As soon as light induction processes occur in the Calvin cycle (as is always the case in fluctuating light (lightflecks) in the half-shade canopy9 this method does not give the answer; but it may support it.....

PAM and IRGA both give PS as mol m^2 s^2 and so you need the leaf area to calculate PS. if you try and calculate PS on a Chl basis you need Chl a per unit area to do it.

Do induction experiments and you can make sense of PAM in unstable light.

Sorry, chlorophyll fluorescence is directly affected by energy dissipation into the electron transport chain - but this is to far away from the site of CO2 fixation, so it won´t work in highly dynamic light environments to yield a CO2 fixation rate, what Dung appears to be interested in....

I would like to take off Mr Dung from this interesting discussion. He said quite a long time ago that he aims to measure photosynthesis of a mangrove forest and neither A or qNP or lightflecks (?). If Dr Kuppers likes he can open a specific question for the 'miss-understading(s)'. John Andrews before Rubisco and later Marylin Ball gave contrbutions to this issue. It was around 1982-84 even if the major citation on Mangrove is Scholaders one about root aerenchima. Today we do not know RGR components of mangroves. I drop this question anyway, cheers.

Thank you so so for the interesting discussion. I gathered much more information than I expected. There are some methods I can't try but others are useful. I found the simple method to do such study. Is English (1997). Although the method is not perfect but basicly I can apply in my lab facility. Again thank you so much for contributing the topic interesting. Cheers