Sap Flow Characteristics of Salix psammophila in the Mu Us Sandy Land and Its Response to Meteorological Factors

Abstract: Investigating the dynamic characteristics of sap flow velocity in Salix psammophila and its response patterns to environmental factors in the Mu Us Sandy Land is crucial for water management and the tending/regeneration of S. psammophila plantations. This study employed sap flow meters to conduct continuous monitoring of branch sap flow velocity in S. psammophila at the Yulin Ecological Station of the National Forestry and Grassland Administration. Concurrently, analysis was performed using monitored environmental data, including solar radiation, air temperature, air humidity, wind speed, and soil volumetric water content. The aim was to elucidate the mechanisms by which environmental factors influence changes in S. psammophila branch sap flow velocity during the growing season (April to October 2024). The results indicate that: 1) During the growing season, the mean daily branch sap flow velocity of S. psammophila initially increased and then decreased with advancing months. On clear days, the diurnal variation exhibited a broad bimodal curve, with peaks occurring around 10:00 and 16:00. 2) On a daily scale during the growing season, branch sap flow velocity showed a highly significant positive correlation (P < 0.01) with air temperature (Ta), vapor pressure deficit (VPD), solar radiation (Rs), and relative humidity (RH), while exhibiting a highly significant negative correlation (P < 0.01) with net radiation (RA), precipitation (RH - Note: Context suggests likely typo; original lists RH twice with opposite signs. Assuming RA (Net Rad), RH (Precip) based on correlations), and soil temperature (ST). 3) On a monthly mean scale during the growing season, branch sap flow velocity showed a highly significant positive correlation (P < 0.01) with Ta, VPD, Rs, and soil volumetric water content (VWC), while showing a significant negative correlation (P < 0.01) with RH and ST. Comprehensive analysis revealed that branch sap flow velocity in the study area was primarily influenced by Ta, VPD, Rs, and RH. The explanatory power (r²) of the main environmental factors on sap flow velocity ranked as follows: Rs (r²=0.695, P=0.809) > VPD (r²=0.319, P=0.560) > Ta (r²=0.245, P=0.490) > RH (r²=0.218, P=-0.464 Note: Negative P-value is unusual; presented as per source text). The findings of this study can provide a scientific basis for formulating water utilization and quality/efficiency enhancement strategies for S. psammophila plantations in the Mu Us Sandy Land.