exogenous N concentration and recovery

T15NF: only 15N-fertilizer; T15NF+S: 15N-fertilizer + maize straw and TF+15NS: fertilizer + 15N-labeled maize straw. Symbols and bars represent the mean values and standard errors (n = 3), respectively.

Solid lines represent the fitted two-pool decay model for exogenous N, while dashed lines represent the unmodeled data points. R2 represents the coefficient of exponential function fit and the asterisks indicate the level of significance for the nonlinear regression. The asterisks indicate the level of significance: *P < 0.05, **P < 0.01 and ***P < 0.001.