Hydrogenenic Photosynthesis: Strategies for animals

Hydrogenic photosynthesis reduces methane and water to build biomass ($\text{CH}_2\text{O}$) and releases hydrogen:

$$\text{CH}_4 + \text{H}_2\text{O} + \text{photons} \to \text{CH}_2\text{O} + 2\text{H}_2$$

For reference, oxygenic photosynthesis is:

$$n \text{ CO}_2 + n \text{ H}_2\text{O} + \text{photons} \to (\text{CH}_2\text{O})n + n \text{O}_2$$

According to this excellent paper by Bains et al, the hydrogenic process is some four times as efficient as the oxygenic version, allowing four times the amount of biomass to be constructed for the same quantity of light (see note *1).

The linked paper describes how large planets could hold onto a hydrogen atmosphere, but this question is not about that.

My question is about strategies for animal evolution, since the flip side of it being 4 times as easy for autotrophs to build mass, is that heterotrophic consumers get 4 times less energy from breaking down one gram of this hydrogenic biomass. Here are the authors words:

"From a purely human point of view, the evolution of hydrogenic photosynthesis might be a disappointing discovery on another world, for reasons implicit in Figure 1. Just as making biomass in an oxidized environment requires more energy, breaking down biomass in an oxidized environment releases more energy. In particular, oxidizing biomass using molecular oxygen releases substantially more energy than reducing it using molecular hydrogen. A commonly-held explanation for the rise of complex animals in the late Pre-Cambrian and Cambrian periods was the rise in atmospheric oxygen that allowed their energy-intensive lifestyles "

My question is; how does the change in 'balance of power' between autotrophs and heterotrophs affect the evolution of both and what is the appropriate animal metabolism to allow animals to display the types of abilities (which rely on storing concentrated energy see note *2) that earth animals display?

Please note - any answer that addresses the fourfold animal vs plant imbalance is valid - PhD level biochemistry answers will be much appreciated but I am not expecting to get many of them!

End of question: what follows is supporting material from the paper that you can treat as **TL;DR.

Note *1

Here is the passage from the paper that makes the claim about reduced biomass generation requirements.

"Comparison of Gibbs energies of formation of CO2 (gas ~ −394 kJ/mol, aq ~−385 kJ/mol) and CH4 (gas ~ −50 kJ/mol, aq ~ −35 kJ/mol) [65] shows that any reaction involving CO2 as the C-bearing reactant will almost always have a more positive Gibbs energy of reaction than a similar reaction with CH4 as the reactant. The quantitative difference between the reactions will depend on the products of the reaction, as illustrated in Figure 1. On average, for the set of chemicals in Figure 1, making the chemical from CH4 takes ~20% the energy needed to make it from CO2. This suggests that building biomass in a CH4/H2-dominated environment would require only ~20% of the energy needed in our CO2-dominated environment."

Note *2

The linked paper mentions that maybe these animals could make use of dimethylsulfonium proprionate (DMSP) to store energy rather than carbohydrate but I don't really understand this process or what its implications are...

posted over 8 years ago

rumguff‭

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