In order to reveal the water consumption characteristics of dominant species-Populus beijing ensis in the arid area of north-west Hebei

the stem flow characteristics of different health grades were studied by thermal diffusion stalk instrument. Meanwhile

meteorological factors

water factors and individual growth status were referred to analyses the driving forces. The results show that there were obvious diurnal changes both in the sunny and cloudy days

the stem flow started early and stopped late in the sunny. The contribution rate of nighttime water consumption of healthy Populus beijing ensis was 2.5%～5.6%

while the contribution rate of unhealthy nighttime water consumption was 8.37%～21.20%. The water consumption of Populus beijing ensis in different health grades were significant different (P＜0.01). The daily average water consumption of unhealthy plants was 22.95±5.99 L

which was only 27.9% of healthy plants. It was positively correlated with solar radiation

air temperature

saturated vapor pressure

and negatively correlated with relative humidity specific

air temperature and relative humidity were the most important. There were timelags between the sap flow in stems and the meteorological factors

the stems flow of health and sub-health individual occurred behind the solar radiation 0.5 h

while ahead of the air temperature

humidity

saturated vapor pressure difference 1 h. For Unhealthy individual

it kept pace withair temperature

humidity and saturation vapor pressure

while behind the solar radiation 1 h. Water consumption of healthy

sub-health and unhealthy individuals of of Populus beijing ensis were 11 636.1

7 254.8 and 425.4 L

respectively. The precipitation of 232.2 mm could not meet the water consumption. It has a stress effect and influences on the grow of Populus beijing ensis because of the lack of water.