All plants, unless they lack roots, can and will take up nutrients from both locations.
This is true for terrestrial plants also, they use fertigation and use sand and bark for nursery production. So they spray and irrigation with KNO3/KH2PO4 etc, it's a 8 Billion $ per year industry here in CA.
Aquatic plants are opportunistic, they can take nutrients from either location, however, K+ is virtually always taken up mostly through the leaves.............rarely through the roots, however, they can do some K+ root uptake also.
So the fact of the matter, in nature and in aquariums, they do both.
If you want to get the bets dosing routine, you'd add nutrients in both locations. Then you have plenty for any situation, and you have more flexibility for the water column should you forget to dose and the sediment will last longer as a source if you dose the water column.
Folks should stop thinking "either.... or", black or white, with or against.
The world and plants are simply not that way. Sometimes folks get caught up in things, and forget their common sense.
Regards,
Tom Barr
