Climatic controls on sap flow dynamics and used water sources of Salix psammophila in a semi-arid environment in northwest China

Abstract

Systematic field measurements were conducted to investigate the relationships between the sap flow of Salix bushes (Salix psammophila) and climatic variables and the sources of water use in the semi-arid Hailiutu River catchment in northwest China. The statistical analyses identified the controls of climatic factors on sap flow and the water use strategy of Salix bushes in periods characterized by different wetness conditions. Correlation analyses indicate strong positive correlations between diurnal sap flow, net radiation, air temperature and wind speed but a negative correlation with relative humidity. The peak values of sap flow occured at the same time as the peak values of net radiation but a few hours ahead of the peak values of temperature and the relative humidity minimum. Multiple regression equations between diurnal sap flow and climatic factors (i.e., net radiation, temperature, relative humidity and wind speed) can account for more than 80 % of the variations in sap flow. Correlation and multiple linear regression analyses between sap flow, soil water contents and groundwater level were used to quantify the water sources of S. psammophila. The results indicate that Salix bushes can use both soil water and groundwater for transpiration. In the dry periods, the cumulative transpiration of Salix caused a continuous decline of soil water contents and shallow groundwater levels. During rain events, sap flow was very low, but immediately after the rain, the peak value of sap flow increased significantly due to better soil water availability. The correlation and regression analysis identified a strong relationship between sap flow and groundwater levels that fluctuated at depths of 145.5-180.7 cm. Therefore, Salix bushes can be considered as groundwater-dependent plants in the Hailiutu River catchment.

Simulation of Water Use Dynamics by Salix Bush in a Semiarid Shallow Groundwater Area of the Chinese Erdos Plateau

“…In contrast, after the rainfall, the soil becomes wet and the ET mainly comes from the soil water. This result confirmed the previous research results using the soil water balance approach at the same site [23]. However, during the simulation with heat flow, the cumulative amount of soil water and groundwater contribution to ET are 32.0 cm and 11.8 cm, which account for 73.1% and 26.9%, respectively, of the total ET (43.8 cm).…”

“…The average annual precipitation is 340 mm, approximately 70% of which occurs between July and September. The average annual potential evaporation is estimated to be 2180 mm [23]. The area's main crop is maize, which is sown in mid-April and harvested in mid-October, with slight variation depending on seasonal weather conditions.…”

“…The area's main crop is maize, which is sown in mid-April and harvested in mid-October, with slight variation depending on seasonal weather conditions. Irrigation depends on local rainfall [23].…”

“…The instruments used in the study are listed in Table 1. Detailed information regarding river catchment and groundwater level measurements can be found in a previous study [23]. Here, the results of a root survey and measurements of soil water content and soil temperature are described.…”

The Relationship between Sap Flow Density and Environmental Factors in the Yangtze River Delta Region of China

“…In China, there has been an increasing research focus on the sap flow characteristics in arid and semi-arid regions, where soil water is limited [39][40][41][42]. Many people think that water shortage problems only exist in arid or semi-arid regions.…”