Hydraulic strategies of desert shrubs responding to morphological adjustment under persistent drought

Abstract

Desertification is one of the most important environmental problems in the world. In arid and semi-arid regions, desert shrub reconstruction is one of the most effective ways to prevent desertification and promote ecological restoration. Recently, many studies have reported the hydraulic trade-off, coordination, and hydraulic segmentation of woody plants, however, the mechanism of how the hydraulic segmentation drives morphological adjustment of desert shrub to response to drought is still largely unclear. Here, the two-year-old seedlings of Caragana korshinskii and Artemisia ordosica as materials were subjected to continuous drought treatment. The aim is to explore hydraulic strategies and quantify the hydraulic threshold when morphological adjustments drive occurs. The results showed that tissues water content of C. korshinskii and A. ordosica under persistent drought showed an exponential decrease with the decrease of soil water content, but it is with a certain lag effect. Meanwhile, the leaf water potential, xylem specific hydraulic conductivity, degree of natural embolism and photosynthetic rate, etc. showed decrease trend with persistent drought. Above results suggested that hydraulic functional traits were drove by changes of soil water, but the tissue hydraulic capacitance acts as a buffer against decline of above traits. Moreover, the water potential thresholds of 88% stomatal closure and hydraulic safety margin in C. korshinskii was significant high than A. ordosica’s, which indicated that C. korshinskii are more vulnerable to drought. Then, the morphological adjustments such as leaf wilting and lateral branches wilting further occurred with the continued drought, however, the lateral branches of C.korshinskii could germinate again after soil water recovery, but A.ordosica could not. Overall, the water potential and hydraulic conductivity threshold for morphological adjustment of desert shrub such as leaves wilting and lateral branches wilting under continuous drought were quantified and the hydraulic strategies were elucidated that was regulated by hydraulic segmentation.