Leave it be :)
Who knows what caused that...
If you do not feed it fertilizer, you rely on the life in your potting mix to provide the nutrients. That life is going through its own cicles and stuff and even though it's all natural and organic and all, there might not be the right nutrients available at the right time, especially if the pot is small - just sayin ...
Organic processes in the soil might cause nutrient spikes or shortages that are totally out of your control.
Do you know about mykorrhiza?
I know a fair bit about it, yes. Is there a particular aspect of mycorrhizal fungi and their relationship with plant nutrition I should understand?
I was just wondering where those should come from and what they would feed on in worm castings and moss :P
In general, I have a feeling that a pot is not big enough to kick off and maintain all processes that would be ideal for a plant.
But if you know a fair bit you are probably ahead of me, anyways :)
Some people buy fungi to add to soil directly, but all dirt has some in it, and it spreads well in most conditions. With some moisture it can grow in most soils, and forms a relationship with plant roots, helping each other absorb and move nutrients. Sometimes I add a little soil from my previous plants to my new pots, to ensure some live bacteria and fungi for the new plants.
You are right, I will have to worry about depleted nutrients toward the end of the plants lives. Thank you for the warning!