The differences in the transpiration of non-irrigated Haloxylon ammodendron in hinterland of Gurbantunggut desert based on diameter

The stem sap flow exhibited a bi-peaked or multi-peaked curve, with lower values at night than during the day. The ambiguous noon-depression phenomenon usually occurs during 14:00~16:00 from mid-May to the early September. Under the same environmental conditions, the larger the stem diameter, the larger the stem sap flow, and the more obvious the ambiguous noon-depression phenomenon. The daily changes of the sap flow were highest in June and lowest in September. There were differences in the monthly mean value in different plants, which may result from the differences in the crown and the number of assimilation organ. The daily accumulation showed a “S” trend between May and the end of August, and showed a straight line with the same slope in September and October. The larger the stem diameter, the larger the daily water use and the accumulative rate were. The sap flow was influenced by meterological factors, it was positively correlated with solar radiation, air temperature and wind speed, and negatively correlated with the air relative humidity, in which the solar radiation had the greatest impact on the sap flow. Under the same environmental condition, the larger the stem diameter, the better the correlation was. The correlation was the largest water use in July, and least in May and October. The larger the stem diameter, the more the water consumption was.