Temporal and spatial variations in transpiration of sunflower leaves in blooming period and its correlation with environmental factors

The studied results of the transpiration characteristics of sunflower leaves in blooming period showed that the transpiration at different leaf positions of sunflower was obviously distinct, and the peak appeared in the leaves from the middle to up at 12∶30 in a day, with the highest value of 23.44μE(H2O)·m-2·s-1 at the 12th leaf, and daily changes of transpiration rate at different leaves appeared single peak curves. The influences of environmental factors on transpiration were comprehensive and the impact of each factor on transpiration was obviously different in daily change. Both photons flux density and leaf temperature had significant positive correlation with transpiration at 8∶30 am, but relative humidity had significant positive correlation with transpiration at 8∶30 am or at 10∶30 am, and at any other time they were not significantly correlated. Photons flux density were negatively correlated with transpiration at 10∶30 am or at 14∶30 pm, but at 12∶30 pm or 18∶30 pm, there was no significant correlation except that leaf temperature was negatively correlated with transpiration at 10∶30 am, they were not significantly correlated at any other time.