Abstract: Under field conditions, the spring wheat(Yongliang-4)growing at different nitrogen levels was used to determine diurnal changes of flag leaf photosynthetic rate(P_n)and its major affecting factors. The relationship between photosynthetic rate and its factors were analyzed with correlation analysis and path analysis. The results indicated that the Pn of both nitrogen levels showed midday depression phenomenon. The Pn at low nitrogen level(60 kg ·hm^-2)varied as a two peaked curve: at 10∶00 and 14∶00. But high nitrogen level(225 kg ·hm^-2)varied as a single peaked curve at 10∶00. Statistical analysis results showed that the photosynthetic depression of flag leaf growing at low nitrogen level was mainly controlled by the stomatal factor.But at high nitrogen level, it was mutually controlled by stomatal and non-stomatal factors. High nitrogen enhances adaptation of spring wheat to strong radiation and high temperature at early filling stage.

Key words: Chinese fir, Continuous planting, Soil microbes, PCR-DGGE, Biodiversity