Quantifying the effects of leaf nitrogen concentration on the maximum leaf gross photosynthesis rate of greenhouse cucumber under different radiation and temperature conditions after flowering

Leaf photosynthesis rate, as one of the most important physiological processes affecting crop yield and product quality, is strongly affected by leaf nitrogen concentration．Experiments with four nitrogen treatments and sowing dates were conducted in greenhouses in Shanghai during 2003 to 2005. The seasonal time course of the optimal leaf nitrogen concentration(N%opt) for photosynthesis was found to be an exponential function of the physiological development time after transplanting(PDT). The relationship between the ratio of the maximum leaf gross photosynthesis rate with nitrogen deficiency (Pgmaxi) to that without nitrogen deficiency(Pgmax0) (PR= Pgmaxi / Pgmax0) and the ratio of the actual leaf nitrogen concentration(N%) to the optimal leaf nitrogen concentration(N%opt) (NR= N%/ N%opt) was also found to be an exponential function. Based on these quantitative relationships, a general model was developed to estimate the effects of leaf nitrogen concentration on the maximum leaf gross photosynthesis rate of greenhouse cucumber under different radiation and temperature conditions. Independent experimental data were used to validate the model. The coefficient of determination(R2) and the root mean squared error(RMSE) between the estimated and the measured maximum leaf gross photosynthesis rate based on the 1︰1 line were 0.83 and 1.56 μmol CO2?m-2?s-1, respectively. The model developed in this study gives satisfactory estimation of the maximum leaf gross photosynthesis rate of greenhouse cucumber growing during different seasons, hence it can be used to optimize nitrogen management for greenhouse cucumber production under different PAR and temperature conditions.