Interannual variation in sap flow response in three xeric shrub species to periodic drought

Extreme seasonal droughts frequently occur in semiarid and arid areas of the world. They can exert a profound influence on the physiological state of desert plants. Short-term rainfall and long-term water shortages in the Mu Us Desert have differentiated the role of individual species with their distinct ability to resist and recover from drought. This study explores how the scale of rainfall events affects interannual variation in sap flow in three dominant desert-shrub species [i.e., Salbc psammophila (SP), Artemisia ordosica (AO), and Hedysarum mongolicum (HM)], and whether the associated changes in soil-water dynamics helped to modify sap flow. As a result, interannual variation in sap flow (J(s)) was mostly driven by precipitation (PPT), Volumetric soil water content (VWC), and leaf area index (LAI), with their individual influences varying as a function of plant phenophases. The species acclimated to long-term summer drought (> 30 days, i.e., no rain over a 30-day period or longer) by reducing stomatal conductance in the three species by 66.5, 59.5, and 43.5%, respectively, suggesting a physiological adjustment in water conservation in response to drought. Average summer drought (June-July) reduced J(s) in the three species by 55.5 (in SP), 42 (AO), and 28.5% (HM), more than spring drought (May-June) at 28% in SP and 9.5% in AO. Among those species, HM exhibited the least sensitivity and the highest overall resistance and resilience to drought. The relationship between J(s) and VWC was modulated by the effect of PPT. Our findings provide compelling evidence that HM is seen to be better suited to future climatic warming, as the species may be capable of accessing deep groundwater reserves replenished by large PPT pulses (5-10 mm), in sustaining its physiological activity over longer periods. These results could help formulate a selection process in determining which shrub species to plant in the sustainable management of desert ecosystems.

Automated summary

Extreme seasonal droughts have a profound influence on the physiological state of desert plants, with different species exhibiting varying abilities to resist and recover from drought. In the Mu Us Desert, long-term water shortages and short-term rainfall events impact the sap flow of dominant desert-shrub species, with precipitation, soil water content, and leaf area index being key factors in driving interannual variation in sap flow. The study shows that different plant species acclimate to drought by reducing stomatal conductance, with Hedysarum mongolicum demonstrating the highest overall resistance and resilience to drought. Additionally, the relationship between sap flow and soil water content is influenced by precipitation, suggesting that certain species may be better suited to future climatic warming in sustaining their physiological activity over longer periods.