The response of sap flow in shrubs to rainfall pulses in the desert region of China

Rainfall pulses can significantly drive the evolution of the structure and function of desert ecosystems, and understanding the mechanisms that underlie the response of desert plants to rainfall is the key to understanding the responses of desert ecosystems to global climatic change. The present study was carried out at the desert-oasis ecotone in the middle of China's Heihe River Basin. We measured sap flow in the branches and stems of desert shrubs (Nitraria sphaerocarpa and Elaeagnus angustifolia) using sap flow gauges, and studied the response of sap velocity to rainfall pulses using the “threshold-delay” model. The results showed that the response of sap flow began about 1 h earlier after rainfall, and that sap velocity increased two to threefold, compared to its pre-rainfall value. The sap velocity increased significantly, then decreased gradually, with increasing rainfall. The response of sap flow differed significantly between rainfall, species, position within species during pulse duration, and the interactive effects also differed significantly (P < 0.0001). The response pattern followed the threshold-delay model, with lower thresholds of ≤5.2 and 1 mm of rainfall for the stems and branches, respectively, demonstrating the importance of small rainfall events (<5 mm) for plant growth and survival in desert regions.