Abstract: Hydraulic anatomical structure plays an important role in the adaptation of plants in arid and semiarid areas. In this study, we used paraffin section method to obtain the anatomical traits of root vessels of four Astragalus herb species (Astragalus adsurgens, Astragalus membranaceus, Astragalus galactites, and Astragalus melilotoides) in arid and semiarid regions of China. Pearson correlation was used to analyze the responses of vessel anatomical features to environmental factors (temperature and precipitation). The results showed that there was great variability in the vessel anatomical traits (vessel number, vessel fraction, mean vessel area, mean hydraulic conductivity, and hydraulic diameter) of Astragalus herbs. With the increases of precipitation and temperature, the vessel number of Astragalus herbs significantly decreased, while the traits related to hydraulic conductivity (hydraulic diameter, mean vessel area and mean hydraulic conductivity) significantly increased, which suggested that Astragalus  herbs from areas with low precipitation and temperature have higher hydraulic safety (more and smaller vessel), while those from areas with high precipitation and temperature have higher hydraulic efficiency (fewer and larger vessel). The correlation coefficients between root anatomical traits and temperature were higher than those with precipitation, which suggested that temperature may be the main climatic factor limiting the anatomical structures of Astragalus herbs in arid and semiarid areas of China.

Key words: hydraulic structure, hydraulic strategy, arid and semiarid areas, Astragalus.