Responses of Soil Water Potential and Plant Physiological Status to Pulsed Rainfall Events in Arid Northwestern China: Implications to Disclose the Water-use Strategies of Desert Plants

Abstract

Abstract Soil water potential (SWP) is vital for plant productivity and ecosystem functioning. This is especially true in arid regions, where rainfall typically falls in brief pulses of variable size. This work aims to improve understanding of the response of SWP to varied rainfall pulses, and of the water-use strategies of a typical desert plant (Haloxylon ammodendron, HA) in arid northwestern China. Rainfall manipulation experiments and field measurements were conducted on HA to explore the response features of SWP and plant physiological status to pulsed rainfall events of varied magnitudes and durations. Multivariate Adaptive Regression Splines (MARS) was used to rank the factors influencing the response patterns of these variables. The response rate and amplitude of SWP increased with rainfall magnitude, and was most affected by three vital factors (antecedent SWP, rainfall amplitude, and rainfall intensity). Very small rainfall (< 2 mm) can increase SWP in the 20-cm layer by nearly 30%, and thus is likely to contribute to the drought relief of HA under low antecedent SWP (< -3.5 MPa), while large rainfall events (> 15 mm) influence deep SWP (60 cm) and enhance the positive correlation between SWP and soil temperature. Very small events play a vital role in maintaining SWP and promoting water use of desert plants. With longer intervals between future rainfall events, HA will tend to improve its water utilization efficiency. Given the nature of plants' utilization of small rainfall events, re-examining ecologically valid SWP thresholds of HA and other similar desert plants is critical.