Abstract: Aims Quantifying the responses of eco-hydrological processes of desert plants to rainfall pulses is the key to understand the impact of climate change in dryland ecosystem. Our objective was to ex-plore the responses of stem sap flow of Haloxylon ammodendron to rainfall pulses in a H. ammodendron plantation in the Ulan Buh Desert. Methods From June to October 2020, the stem sap flow of H. ammodendron, micrometeorological factors and soil moisture in the plantation were continuously observed by thermal diffusion probes as well as the hydrometeorological methods, to analyze the characteristics of stem sap flux density (SFD) of H. ammodendron and its response to rainfall. Important findings (1) The average daily SFD was 0.044 g·cm-2·min-1 after the rain, which was 1.16 times of that before the rain among the selected 17 rainfall events during the study period. The diurnal variation of SFD were changed from “bimodal pattern” before rain to “unimodal pattern” after rain for 9 of the all events. The characteristic value of daily SFD fluctuation were obviously changed after the other 8 rains. For example, the initiation time of SFD after rain were earlier from 8:00 before rain to 7:00 in the morning. And its peak values of daily SFD were also increased from 0.067 g·cm-2·min-1 before rain to 0.085 g·cm-2·min-1, and the duration of the peak interval was significantly extended. (2) The impacts of rainfall pulses on the sap flow of H. ammodendron could be well described with the threshold delay model (T-D model). And the lowest rainfall threshold and the lag time of SFD responded to rain were 0.8 mm and 1.71 d, respectively, indicating that the sap flow of this shrub species was sensitive to rainfall pulses and had a certain lag. (3) The SFD of H. ammodendron was significantly positive correlated with atmospheric temperature, vapor pressure deficit, solar radiation, wind speed and soil volumetric water content, and significantly negative correlated with the relative humidity, but no significant correlated with rainfall, suggesting that SFD of H. ammodendron would be indirectly affected by rainfall pulses by changing the physiological characteristics of the species as well as soil water condition. Our results are helpful to further understand the water use characteristics of desert plants and their response to climate change, and are of great significance for the sustainable management of artificial sand-fixation forests in future.

Key words: rainfall pulses, Haloxylon ammodendron, sap flow, soil moisture, threshold-delay model