Growth cost in Nostoc 7120; growth dynamics of resistant substrains of Nostoc 7120 and their susceptible controls in nitrogen replete (A) and in nitrogen deplete conditions; (B) the growth of the resistant substrains in nitrogen-rich medium was significantly lower than that of the susceptible wild type for RD1, RD2, and RE1 (P < .001); the resistant substrains RD2, RE1, and RE2 had a significantly greater cost under nitrogen starvation than in nitrogen replete medium (P < .001); data shown are average +/− standard deviation of five biological replicates; relative cell density is estimated by chlorophyll a autofluorescence; A.U: arbitrary units.