Source traits are an ensemble of traits that define how sources behave. This affects things like the amount they can hold or the speed it takes for them to recover. You can see source traits by using a source analysis glass.
Capacity: The element capacity of the source, the bigger the capacity the longer it will take to exhaust and replenish the source.
Diurnal: Increased recovery speed during the day, decreased recovery speed during the night.
Nocturnal: Increased recovery speed during the night, decreased recovery speed during the day.
Generous: Increased extraction speed from the source.
Selfish: Decreased extraction speed from the source.
Thrifty: Decreased element loss when extracting from the source.
Wasteful: Increased element loss when extracting from the source.
Fertile: Reduced element cost of source seeds.