Asian Journal of Research in Botany

Stomatal characteristics and xylem anatomy play a central role in regulating plant water relations and gas exchange, particularly under water-limited environments. The present study examined interspecific variation and coordination between leaf stomatal traits, Potential Conductance Index (PCI), and wood anatomical characteristics in Citrus reticulata and Citrus sinensis grown under the semi-arid conditions of Mubi, Adamawa State, Nigeria. Stomatal size, stomatal density, epidermal cell density, stomatal index, and PCI were quantified from leaf epidermal impressions, while vessel and fibre dimensions were measured from stem wood samples. Data were analysed using independent sample t-tests. Significant interspecific differences were observed in most stomatal parameters. C. reticulata exhibited significantly higher stomatal length, width, density, and PCI, indicating a greater anatomical potential for gas exchange. In contrast, C. sinensis showed a significantly higher stomatal index but lower PCI. Wood anatomical analysis revealed that vessel length and vessel width were significantly greater in C. sinensis, whereas fibre length did not differ significantly between the two species. Several traits, including stomatal pore dimensions, also showed no significant interspecific variation. The contrasting patterns of higher PCI in C. reticulata and larger vessel dimensions in C. sinensis suggest species-specific coordination between leaf-level gas exchange potential and stem hydraulic architecture under semi-arid conditions. These findings highlight differing adaptive strategies in Citrus species and underscore the importance of integrating stomatal and xylem traits to better understand plant responses to water-limited environments.