Temporal Patterns And Environmental Controls Of Sap Flow For Three Typical Desert Shrub Species

Knowledge on the responses of sap flow (i.e., transpiration) to environmental factors in arid/semiarid ecosystems contributes to the understanding of plant physiological adaptation to water and heat stress, and may assist in the vegetation recovery in desertified areas. Sap flow in Artemisia ordosica, Salix psammophila, Hedysorum leave maxim, together with environmental variables and biotic factors, were continuously measured in situ from2012.1. Weather conditions exerted a strong control over the diurnal pattern of sap flow in Artemisia ordosica. The daily maximum sap flow rate107.81,79.40, and4.34g·cm-2·h-1on sunny, cloudy and rainy days, respectively.2. The sap flow rate in Artemisia ordosica, Salix psammophila and Hedysorum leave maxim had distinct diurnal variations, exhibiting single-peak curve in the typical sunny weather conditions. The sap flow of three species started at6:00while stopped at20:00, and reached the peak value at13:00,10:30and10:30, respectively. There was no obvious sap flow at night for Artemisia ordosica, but for both Salix psammophila and Hedysorum leave maxim. Sap flow showed pronounced seasonal variations, the monthly average sap flow was the maximum on July and was minimum on October.3. The key factor affect plant sap flow is different in different periods. During drought periods, daily sap flow rates showed strong correlation with soil water content for all three species. Under higher soil water conditions, vapor pressure deficiency and air temperature were the two vital factors affecting the daily sap flow rate for Artemisia ordosica and radiation for Hedysorum leave maxim. Vapor pressure deficiency and solar radiation were the most important factors for Salix psammophila during the expanded leaf period. Leaf area was the key factor to affect the sap flow for Salix psammophila during both leaf expanding stage and leaf defoliation stage, and for Hedysorum leave maxim only during leaf defoliation stage.The results indicated that the water consumption of transpiration of Salix psammophila is less than the Artemisia ordosica and Hedysorum leave maxim. However, Artemisia ordosica is the shrub that the least affected under water stress compared the other two species and exercised stronger adjustment capacity than the other two shrubs. Three kinds of shrubs don’t absorb a lot of groundwater under the drought stress to maintain high sap flow, but reduce the stap flow and rely on its strong fine root system or horizontal roots absorption surface soil moisture to resist drought.