A comparative study of vessel length measurements in branches of eight subtropical woody species based on three methods

Vessel length in xylem of woody species is a key functional trait for understanding water transport mechanisms, directly influencing xylem hydraulic efficiency and safety. However, the accurate measurements of vessel length are susceptible to methodological variations. This study employed silicone injection, air injection and pneumatic method on eight subtropical woody branches to compare their applicability, accuracy and limitations for measuring vessel length and its distribution pattern. The results demonstrated that the vessel length distribution curves in three methods all showed an asymmetric unimodal right-skewed distribution. Both mean and mode vessel lengths of eight species obtained from the pneumatic and air injection methods showed no significant differences and were all higher than that from the silicone injection method. Besides, across all vessel diameter ranges in eight species, both mean and mode vessel lengths showed significant positive correlations among the three methods. However, the correlations became weakened in wide vessel species, especially for the silicone injection data. Moreover, vessel lengths were significantly positively related to the vessel diameter in eight species. This study provides empirical evidence for selecting appropriate methods to measure vessel length, which has a crucial role in determining water transport functions in the xylem of plants.