Initial Chl a concentrations and maximum response in the different treatments (control, + N, + P, and + NP) of the nutrient limitation experiment in Lake Wuli. N is nitrogen addition, P phosphorus addition, and NP nitrogen and phosphorus co-addition. Error bars indicate ±1 SD of four replicates. Differences between treatments are based on ANOVA post hoc tests (a > b > c > d; P < 0.05).