Dynamics of sap flow of Populus euphratica and responses to environment variables in the southeast of the Kumtag Desert

In this study, the PS-TDP8 tree stem sap flow monitoring system was used to study the sap flow of Populus euphratica (the Euphrates or desert poplar) in the southeast of the Kumtag Desert from April to October in 2018 (spring April, summer July, autumn September). Correlation analysis and stepwise regression method were used to analyze the influence of meteorological factors (total solar radiation, air temperature, wind speed, relative air humidity) on the sap flow of P. euphratica. The results showed that the diurnal sap flow variation trend of P. euphratica displayed a "broad peak type". Sap flow in summer had the earliest start time, and the sap flow started at 06:00 in the morning, while the sap flow started at the latest in autumn. There was high sap flow velocity in all seasons at night. The trunk sap flow velocity was positively correlated with solar radiation, air temperature, wind speed, and saturated water pressure difference, while negatively correlated with air humidity. The main meteorological factors that affected the flow velocity of P. euphratica in spring and autumn were total solar radiation and air temperature, while those in summer were total solar radiation and relative air humidity. The response of P. euphratica sap flow velocity to air temperature, air relative humidity, wind speed, and saturated water pressure difference was clockwise in different seasons, and the asymmetry of the response to solar radiation was counterclockwise. The response of P. euphratica sap flow velocity to meteorological factors difference is different in different seasons, indicating that P. euphratica has different strategies to cope with water deficit to maintain water balance, and reduce water loss through stoma regulation under certain conditions (e.g., extreme drought in summer). The current results are of great significance for clarifying the water transpiration response of P. euphratica to environmental factors in arid desert environments and for a deeper understanding of the water use strategy of P. euphratica to adapt to arid environments.