Let’s try to make this conversation more concrete so that we have a better understanding of just how to deal with internal part upgrades.
I think the question is how to introduce sulfate and nitrate in a way that makes it a bit more interesting than just adding another compound into the game, because we honestly would have enough parallels with other metabolic strategies to make things a little repetitive.
Let’s first focus on nitrate to make a more defined concept and figure out where there is gridlock.
Nitrate
Nitrate - specifically, denitrification - is an essential part of the Nitrogen Cycle. Nitrate is broken down by nitrate reductase to create atmospheric nitrogen, which is then converted into ammonia via either nitrogen fixation (converts atmospheric nitrogen to ammonia) or ammonification (converts organic nitrogen to ammonia). Ammonia is then converted into nitrite/nitrate via nitrification, and then the process starts again, with nitrate reductase breaking down nitrate into atmospheric nitrogen. It is important to note that there are non-biological processes which facilitate parts of the cycle as well; lightning can split nitrogen, allowing it to bond to oxygen to result in the formation of nitrate.
So at a very broad level, this is the ABC’s of the nitrogen cycle…
- Nitrogen gets turned into ammonia (nitrogen fixation or ammonification).
- Ammonia gets turned into nitrite/nitrate (nitrification).
- Nitrate/nitrite gets turned into nitrogen (denitrification).
- Repeat.
In Thrive
The fundamental idea is…
Adding Nitrate: A new atmospheric compound.
Adding Nitrogen Reductase/Denitrification: Breaks down glucose via utilizing nitrate as an electron acceptor. Rate scales with atmospheric nitrate. Results in nitrogen. Essentially metabolosome but utilizing nitrate instead of oxygen to burn glucose.
This will allow Thrive to have a solid anaerobic option for breaking down glucose while also adding more flesh to a very important ecological process. Fleshing out this system can result in an interesting dynamic where ammonia, nitrate, and nitrogen interact to create shifting “supplies” and “demands”. For example, an environment filled with nitrogen-fixating organisms would probably benefit from organisms who denitrify nitrate, as nitrogen-fixation depends on a supply of accessible atmospheric nitrogen. Not having denitrification could result in a reduction of the viability of nitrogenase and related parts as nitrogen reduces in supply.
Problem
The bad news is that the step before denitrification - nitrification, which results in the creation of nitrate - is largely a biological phenomena. This would mean that the nitrogen-cycle wouldn’t be a completely closed loop It would be quite a scientific gloss-over to have nitrogen-fixation directly feed into the supply of nitrates.
Nitrification itself essentially involves the breakdown of ammonia with oxygen to create energy. So implementing nitrifying bacteria would allow those cells to use ammonia as a food source instead of solely as growth compound. This sounds like it might be a lot for the game to handle and could result in a mess related to the growth mechanics, so I’m pretty iffy on this.
Potential Alternatives
Perhaps we can treat nitrate as a compound with a rather limited supply that gets introduced via environmental factors. While nitrification itself is largely a biological process, there are some abiotic processes which can result in the creation of nitrate/nitrite. For example, atmospheric chemical reactions or thunderstorms can create nitrate.
Maybe we can treat nitrate as a compound that gets introduced at random points due to environmental factors, which gets eaten up the more nitrate-respiring organisms are present? That would definitely be a unique mechanic which could make living as part of the nitrogen cycle a bit of a different gameplay experience.
It would also kind of make ammonia act as a limiting nutrient, which is a very important ecological concept which would be very cool to implement in Thrive. Since nitrogen-fixation reduces nitrogen supply, and since nitrate respiration increases nitrogen supply, there could be moments in Thrive where a saturated nitrogen-fixation niche within a compound reduces the amount of nitrogen available in the environment to reduce the total presence of free-floating ammonia. Less nitrogen available does mean less powerful ammonia production after all. Then, the environment would really benefit from a potential nitrate shock, where denitrifying bacteria reintroduce a good amount of nitrogen to the environment, thus driving ammonia supply back up.
The only issue is that, once again, nitrification is heavily dependent on biological processes, so it might be a bit too far from reality to make nitrate seem like a compound that relies heavily on non-biological processes.
Good News
Some good news I have for you guys is the fact that implementing a very simple representation of the sulfur cycle is possible in a relatively non-convoluted implementation…
Implement Atmospheric Sulfur - Would be present as a gaseous, atmospheric compound similar to nitrogen and oxygen.
Implement Sulfur Reduction - Uses sulfur instead of oxygen as an electron acceptor to oxidize glucose, resulting in the creation of hydrogen sulfide and energy. Essentially metabolosomes, but using sulfur instead of oxygen to burn glucose and releasing hydrogen sulfide instead of carbon dioxide as a by-product.
Since sulfide chemosynthesis results in the release of sulfur, and sulfur reduction results in the creation of hydrogen sulfide, we can have a very simple sulfur cycle. Attaching certain environmental effects to sulfur would reinforce the impact of the sulfur cycle on biogeochemical processes.
If nothing else, we can rely on the sulfur cycle as an answer to the pre-oxygenic glucose problem. If we want to, we can implement the nitrogen cycle in ways other than using it as a significant metabolic option, since that opens up various issues. Sulfur respiration is apparently a very ancient form of metabolism anyways.