Talk:Photosynthetic efficiency

Efficiency undefined

This article does not define the term 'Photosynthetic efficiency'. Which photons are counted? Those which are absorbed by the leaf? Those which excite a chlorophyll molecule?

Note that a green photon has energy roughly 400 pN nm. It can allow the synthesis of two ATP molecules which under physiological conditions store an energy of 100 pN nm each. That's an efficiency of 50%. Wow! It really depends on how you count. [I used picoNewton times nano meter as energy unit; note4 pN nm = 10^-21 Joule].

Unsigned comment from User:193.174.246.180, 22 January 2009.

The abstract from Photosynthesis in Sugarcane Varieties Under Field Conditions1 -- Irvine 7 (4): 297 -- Crop Science uses rates of photosynthesis per unit of leaf area, presumably assuming some model of standard solar illumination (noon, equatorial, clear sky, mean humidity?) Full text is behind a coin-op. Maybe someone from inside the palace walls can dig into this. Other sources discuss yield per acre over a growing season, which is quite a different thing. It doesn't make much sense in the context of biology to talk about excited molecules; that's more interesting from the perspective of a solar chemist. Plants seem not to want to get too excited, and go to some lengths to avoid spectrum they can't handle. MaxEnt (talk) 20:50, 1 November 2009 (UTC)

"Efficiency" is defined as energy out divided by energy in.

With that said, there are a number of possible ways to chose what energy out is being considered (including energy used by the plant? Just energy stored in the form of carbohydrates?), and for that matter, several ways to define energy in (Correctly, this should be total energy incident on the leaf, but some people may chose to only consider the energy absorbed by the plant, and molecular chemists may sometimes only consider the energy absorbed by the chlorophyl molecule. So this does need to be clearly stated.) Geoffrey.landis (talk) 18:43, 31 March 2019 (UTC)

Photosynthesis Efficiency of other popular Bioenergy crops

I would suggest to at least list the efficiency of rape (canola), palm oil and algae (due to current popularity) as well. I cannot find values, though.Anyone? --Asdirk (talk) 08:36, 11 September 2009 (UTC)

The "Efficiencies of Various Energy Crops" is horribly written and has half-assed references. —Preceding unsigned comment added by 131.215.52.116 (talk) 07:50, 8 January 2010 (UTC)

Possible miscalculation in "Worldwide Figures" section

In the section titled "Worldwide figures", the current (as of 22 SEP 2010) article reads:

"According to the cyanobacteria study above, by simple math, this means the total photosynthetic productivity of earth is between ~1500-2250 TW, or 47,300-71,000 exawatts per year...."

Unless I am mistaken, I think that there are at least two numeracy problems with this statement: 1) The "per year" value is stated in units of power (exaWatts) when it should be units of energy (e.g. exaWatt-hours). 2) The conversion from the instantaneous power production (~1500-2250 TW) to annual energy production (47,300-71,000 exawatt[-hours?] per year) seems to be WAY off in order of magnitude. An exaWatt is 10^6 (one million) times larger than a terraWatt. If one assumes that the instantaneous production of photosynthetic power only occurs during daylight hours, there would be ~12 hrs/day (~4380 hrs/year) of photosynthetic power production. Which would result in ~6570-9855 petaWatt-hours per year (vice the values listed for exaWatts, off by ~8000x).

I did not correct this in the article because: a) The error appears so gross that I think I might be completely missing something b) I'm not sure which value is correct (the initial claim of ~1500-2250 TW of power, or the value of per annum "power" (which, again, I think means energy).

Assuming the latter is incorrect, and needs to be corrected, I suspect all the remaining figures in the paragraph might need to be corrected as well (but I'm not sure of the source of those claims or the math used there). —Preceding unsigned comment added by 138.162.0.43 (talk) 14:49, 22 September 2010 (UTC)

Sugarcane efficiency way off

measuring

Efficiency

Double mention

Clearer Citation Needed

In the sentence "From a 2010 study by the University of Maryland, photosynthesizing Cyanobacteria have been shown to be a significant species in the global carbon cycle, accounting for 20–30% of Earth's photosynthetic productivity and convert solar energy into biomass-stored chemical energy at the rate of ~450 TW.[7]", Reference 7 is not the actual source of the quoted figure, but references it as coming from the following source:

Waterbury JB, Watson SW, Guillard RRL, Brand LE. Widespread occurrence of a unicellular, marine, planktonic, cyanobacterium. Nature. 1979;277:293–294

I don't have access to this; can anybody check this reference and give the correct source? Other sources give much lower values for the total photosynthesis productivity, e.g., https://bioticregulation.ru/common/pdf/energy08.pdf lists 100 TW. Geoffrey.landis (talk) 18:43, 31 March 2019 (UTC)

I looked up the Waterbury article in Nature and it contains no statements at all about global photosynthetic productivity or global energy storage rates. As its title suggests, it's just a report on finding a certain type of cyanobacteria, in certain quantities at various depths, in two different parts of the world. This makes Reference 7 (Pisciotta et al.) highly suspect and as you say, 450 TW seems way out of line compared to other estimates. 65.130.7.225 (talk) 06:39, 3 November 2023 (UTC)

And I am deleting the following sentence: "According to the electron yield of 0.05% to 0.3% mentioned in the cyanobacteria study above[7], this means that a gross upper-bound estimate for the total photosynthetic productivity of earth is between ~90–530 TW (see also Earth's energy budget), if all of earth's surface was photosynthetically active."

This is not actually what the source says, but rather a back-calculation, and one I can't make sense of: the figures are inconsistent. 450 TW can't possibly be "20-30%" of a total of 90-530 TW.

The electron yield is not a useful number; it's the number of electrons per photon, not the energy out/energy in. Since the photons in range from very low energy infrared (which aren't absorbed at all, but still have to be counted) through visible and up to near-UV, you need more data to turn this into something useful here. Geoffrey.landis (talk) 18:55, 31 March 2019 (UTC)

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