Phenotypic, physiological and transcriptomic dynamics of Caragana liouana in a chronosequence of revegetated areas in Ningxia, Northwest China.

Caragana liouana, a xerophytic shrub endemic to the arid and semi-arid ecotones of northwest China, exhibits remarkable ecological resilience and restoration potential. As a pioneer species in vegetation rehabilitation chronosequences, its multi-decadal afforestation history provides an ideal chrono-biological system for investigating eco-physiological adaptations under environmental stochasticity. Through integrative analysis of phenotypic plasticity, physiological homeostasis and transcriptomic reprogramming across four plantation age gradients (chronosequence approach), we elucidated the species' adaptive strategies to long-term drought acclimation and thermal stress. The results showed that height, crown, relative water content (RWC), specific leaf area (SLA) and chlorophyll content significantly decreased, while diameter, stem/leaf (S/L) ratio and lignin content significantly increased with plantation age (p < 0.05), with particularly pronounced changes between 25a C. liouana plantation and 46a C. liouana plantation. These allometric adjustments reflect an age-dependent shift in resource allocation. Our principal finding reveals that 46a C. liouana plantations exhibit diminished drought resistance and photosynthetic capacity, whereas 25a C. liouana plantations demonstrate optimal drought adaptation and photosynthetic performance with minimal lignification. Collectively, C. liouana employs age-specific strategies, prioritizing structural reinforcement over photosynthetic acquisition and coordinating leaf functional trait trade-offs to enhance fitness in arid environments. Simultaneously, transcriptomic analysis revealed 20,065 differentially expressed genes. Three gene modules, highly correlated (|correlation coefficient| ≥ 0.60) with height, SLA, S/L ratio, and lignin content, were primarily enriched in biosynthesis of secondary metabolites, plant hormone signal transduction, and MAPK signaling pathways. Importantly, gene interaction network analysis revealed 13 hub genes that play pivotal roles in modulating the physiological and developmental processes underlying these age-dependent adaptations. In conclusion, the study shows that plantation age significantly correlated with the drought adaptation of C. liouana, with 25a plantation displaying optimal physiological performance, driven by distinct transcriptomic reprogramming involving key signaling pathways and hub genes. These findings not only provide a theoretical basis for plantation management and conservation, but also provide novel insights into current plant adaptations to future climate change.