Intraspecific variability of ecophysiological traits of four Magnoliaceae species growing in two climatic regions in China

Plants may change their ecophysiological traits to adapt to new environments, but the responses strongly depend on species and environmental conditions. Magnoliaceae species are of great scientific importance but are extremely endangered, therefore, it is crucial to study their ecophysiological adaptations for ex situ conservation. Here, we chose four common Magnoliaceae species growing in two botanical gardens located in south and north subtropical monsoon regions, and measured hydraulic and photosynthetic traits in both wet and dry seasons. We found that plants growing in north region showed significant lower leaf water potential at predawn and midday than those in south region, indicating that species suffered more severe drought stress in north region. As a result, species in north region had lower stomatal conductance and photosynthetic rates, as well as smaller stomatal pore index. In addition, significantly lower stem hydraulic conductivity of the two deciduous species in north region were observed compared with species in south region, while the two evergreen species at both regions showed similar values of stem hydraulic conductivity. Non-significant differences in leaf turgor loss points, leaf conductance, specific leaf area, and wood density were found when comparing species from the north and south regions. Our results suggested that the adjustment of plant hydraulics to local climatic conditions of Magnoliaceae species occurs primarily through changes in stomatal morphology and function, whereas the contribution of intraspecific variation in leaf hydraulic traits appears to be limited.