Table 1. Overview of axenic culture experiments testing the effects of N forms and concentrations on plant growth. Experiment 1 consisted of a concentration series with 1.67 to 45 μM protein (BSA, 66 kDa, 15% N) added to nutrient-replete half-strength MS medium (20 mM IN-N). Experiment 2 provided N as low or replete IN (4 or 20 mM IN-N) or as low IN + protein (4 mM IN + 16.1 mM protein-N).

mg BSA per ml growth medium	BSA (μM)	BSA-N (mM N)	IN (mM N)	total N (mM N)	total N (mg N perplate)
Experiment 1
-	-	-	20	20	8.4
0.11	1.67	1.2	20	21.2	8.9
0.33	5.0	3.6	20	23.6	9.9
1.0	15	10.7	20	30.7	12.9
1.5	23	16.1	20	36.1	15
3.0	45	32.1	20	52.1	21.9
Experiment 2
-	-	-	20	20	8.4
-	-	-	4	4	1.7
1.5	23	16.1	4	20	8.4