is available under creative commons and it has a wonderful picture of the fluxes in a tree. Here is the picture text:

“Overview of processes and factors determining the isotope signature of C pools and fluxes in space and time in the plant-soil-atmosphere continuum. White boxes represent pools, gray boxes show fractionation or other processes determining the C isotope composition of the involved compounds”

My plan was to add this to the Isotope geochemistry page .But maybe we could mention this in ths blog or an upcoming on earth biomass part of the carbon cycle?

Nitrogen is indeed the really interesting element in this game: my own remarks dodged it and focused on C, H, and O!

But when they say 90% of the biomass comes from the atmosphere, I’m a bit suspicious: does ‘the atmosphere’ include water? Trees are mostly lignin, cellulose and other carbohydrates; the carbon and oxygen can come from air, but the hydrogen has to come from water (and probably a bunch of the oxygen does too).

Of course most water used by trees comes from rain—which comes from the atmosphere. So, they could still be correct in a technical sense.

At the end of the 19th Century, the argument shifted to where do plants get their nitrogen? Crop rotation and legumes provided some, but guano was imported in vast amounts from South America for use as fertiliser. Using sewage on the land, as proposed by Liebig, provided only low levels of nitrogen and Crookes gave a famous British Association lecture warning of a food crisis ahead. The Times carried a spirited correspondence by Liebig and others on the merits of using sewage from London outfalls on the land. In reality sewage has less value than might be expected. The outbreak of the European War (WW1) in 1914 led to a blockade of sea routes which hastened German industrial production of ammonia in by the Haber-Bosch process.

Today 40-60 per cent of the nitrogen in the human body has its origin in synthetic ammonia from the Haber-Bosch process. (I’d confirm the Nature 2004 reference but it’s paywalled). I like to tell my more green friends they are in part a product of high-pressure chemical engineering :)

Apologies Staffan, a bit off-topic from Box Models …

I don’t think you can infer much from the need for nutrients or fertilizers. They be necessary to participate in some critical reactions, but that doesn’t mean that they’re a large fraction of the mass.

The fact that fertilizers are needed and that eroded soil has a reduced crop yield seem to imply that a considerable amount of mass does transition from the soil to the plants.