Xylem anatomical structure as a determinant of hydraulic trait variation in C3 plant Reaumuria soongorica and C4 plant Salsola passerina

Abstract

Moisture variation significantly impacts hydraulic traits and xylem anatomical structure in woody plants, thereby influencing water transport and embolism resistance. However, the precise relationship between these factors within desert shrubs remains unclear, and it may be related to plant functional types. We conducted a water manipulation experiment involving seedlings of the C₃ plant Reaumuria soongorica and the C₄ plant Salsola passerina within a rain shelter. We applied three water treatments: control, chronic drought, and flash drought. After a period of drought treatment, seedlings were rewatered to control level for 15 days, after which hydraulic traits and anatomical structures were measured. We found that: (1) vessel density was positively correlated with sapwood specific conductivity for R. soongorica, while hydraulic weighted vessel diameter positively correlated with embolism resistance; both hydraulic weighted vessel diameter and vessel internal diameter span was positively correlated with sapwood specific conductivity for S. passerina; (2) R. soongorica had lower edge density yet higher modularity compared to S. passerina; (3) sapwood and leaf specific conductivity emerged as hub traits in R. soongorica, while vessel internal diameter span was identified as a hub trait in S. passerina, thus serving as important predictors of hydraulic function and related attributes. Our study demonstrates distinct hydraulic strategies in the two species. R. soongorica employs a highly modular trait combination to adapt to water fluctuations, maintaining both high hydraulic efficiency and embolism resistance under drought stress. Conversely, S. passerina integrates traits for efficient resource access, ensuring hydraulic efficiency but compromising embolism resistance under drought stress. Integrating hydraulic traits with anatomical structures significantly enhances predictions of desert shrub resilience to drought within the context of global climate change.