First, on the macroalgaes - yes. NH4, NO3, Aminos is the order of preference, and fast growing algae can really ramp up their NH4 uptake if the opportunity presents itself.
This paper:
"Uptake of urea and amino acids by the macroalgae Ulva lactuca (Chlorophyta) and Gracilaria vermiculophylla (Rhodophyta)"
has some really interesting stuff. One takeaway is that Amino acids get uptaken faster (generally) if they have a smaller side-chain. (see fig 3)
The paper talks about the algae having to break down the amino for absorption to get the ammonia part it wants. makes sense.
That makes sense. The dino part is kinda mindblowing though.
From the "putting the N in dinos" paper
"Generally, when growing in presence of various different N compounds, dinoflagellates (as well as plants and algae) prefer to take up NH+4. However, there is a concentration threshold above which NH+4becomes toxic to the cells, and this threshold seems to be species-specific. For example, in
A. minutum, NH+4 concentrations of 25 μM and higher lead to growth inhibition while for
A. tamarense and
Cochlodinium polykrikoides, this threshold was not observed until 50 μM"
That's like 0.5 ppm ammonia, weirdly low. anyway... on to good stuff.
"Another tendency in dinoflagellates is inhibition of NO−3 uptake when in the presence of NH+4. In
A. minutum, this inhibition was found to be greater when the cells were in N-sufficient compared to N-deprived conditions. This suggests that when N is limiting, uptake of different forms will be favored over strict assimilation of NH+4 which has a reduced energy cost.
Curiously, different blooming populations of dinoflagellates were found to have high uptake rates for urea and/or amino acids, and these rates were always higher than the rates for NO−3 uptake. In L. polyedrum, the urea uptake rate was also about 2 times more than that of NH+4, even if environmental urea concentrations were less than NH+4. Taken together, these observations suggest that dinoflagellates possess a full suite of transporters for inorganic N and organic N forms, that they have the biochemical means to assimilate these N forms, and that they show a great physiological plasticity in response to external N types and concentrations.
Dinos better at taking up big organic N forms than straight ammonia? Super weird.
So Algae preference: Ammonia, Nitrate, Aminos
Dino preference: Aminos, Ammonia (as long as it's tiny), Nitrate