Abstract: With pot culture, the physiological responses of cotton plant to fertilizer nitrogen at flowering and boll-forming stages were studied under soil drought and after re-watering. The results showed that under soil drought, the net photosynthetic rate (P_n) and transpiration rate (T_r) declined rapidly with decreasing soil relative water content (SRWC). At the early stage of soil drought, owing to the declining degree of T_r was greater than that of P_n, the WUE had an increasing trend; but after then, the WUE decreased with declining SRWC and P_n. Soil drought altered the diurnal patters of P_n and T_r, i.e., decreased continuously from 8:00 to 16:00, while in CK, their peak values appeared at 10:00-11:00 and 12:00, respectively. The diurnal patterns of WUE in drought treatment and CK were the same, i.e., decreased first and increased then, with the bottom appeared at 12:00. Under soil drought, the P_n and T_r decreased with increasing fertilizer nitrogen level, while WUE was in adverse. After re-watering, the diurnal patterns of P_n, T_r and WUE were similar to CK, but their values were smaller than CK, especially under nitrogen application. It was suggested that under soil drought, nitrogen fertilization could be helpful to the increase of water use efficiency, but decreased the photosynthesis of cotton plant at its flowering and boll-forming stages.

Key words: Poncirus trifoliata, root hair, hydroponics, growth and development, nutrient.