We studied the effects of N on submersed macrophytes represented by Vallisneria natans (Lour.) Hara in pots positioned at three depths (0.4 m, 0.8 m, and 1.2 m to form a gradient of underwater light conditions) in 10 large ponds having moderate concentrations of P (TP 0.03 ± 0.04 mg L_1) and five targeted concentrations of total nitrogen (TN) (0.5, 2, 10, 20, and 100 mg L_1), there were two ponds for each treatment