C content in Humic & fulvic acids

Question: Was just confused about the carbon content in humic acid. On lecture 8, there is picture that says that humic acid has a higher carbon content compared to fulvic acid but on the next slide it says that humic acid has a lower number of carboxyl groups per unit mass than fulvic acid. I am a little confused about this. The important concequence of this is that humic acids will be more difficult to decompose by soil microorganisms, and that release of plant available forms of nutrients (eg N, S, P) will be slower.

Answer: In organic compounds, C can be present in some (but not all) functional groups (eg COOH group), but C is also present in open chains and cyclical rings. Hence, statement that humic acids have higher C content than fulvic acid is in agreement that humic acid molecules are larger and of larger molecular weight (and also more complex) than molecules of fulvic acids.
In addition, one needs to keep in mind that humic acid has lower number of COOH groups (and other functionsl groups) per unit mass.