Concentration of phenolic compounds of Populus euphratica and soil water contents in Ejina oasis, Inner Mongolia, China

With colorimetric methods, the concentrations of total phenolics, flavonoids and condensed tannins were analyzed in 9 categories of organs in Populus euphratica, including lanceolate leaves, ovate leaves, green branches, branches (D < 5 mm in diameter), branches (5–10 mm in diameter), barks, roots (D < 2 mm in diameter), roots (2–5 mm in diameter) and roots (5–10 mm in diameter). The results showed that phenolic compounds were present throughout the collected organs with the higher total phenolics concentrations in barks (27.93 mg/g), and the mean total phenolics concentrations in two categories of leaves, three classes of roots and three classes of branches were 17.64, 16.72 and 12.19 mg/g, respectively. The higher flavonoids were present in barks (51.30 mg/g), and the mean flavonoid contents in two categories of leaves, three classes of roots and three classes of branches were 28.45, 39.99 and 23.67 mg/g, respectively. The higher condensed tannin contents were found in roots (mean = 22.10 mg/g for three categories of roots), and the average condensed tannin contents in barks, leaves in two categories and branches in three classes were 8.41, 4.03 and 4.47 mg/g, respectively. There was no significant difference between the phenolic compounds of lanceolate leaves and ovate leaves (P > 0.05). Phenolic compounds in branches decreased with the branches maturing, resulting in the following orders: green branches > branches (D < 5 mm) > branches (5–10 mm). Condensed tannins in roots increased with the root diameter decreasing, and the highest condensed tannin contents were found in small roots (D < 2 mm) (25.95 mg/g). By analyzing correlation between phenolic compounds in all collected organs and soil water contents, it was indicated that the phenolic compounds in ovate leaves had negative relation with soil water contents (P < 0.05), and the r values for total phenolics, flavonoids and condensed tannins were –0.949, –0.923 and –0.944, respectively. Data reported here revealed the variation of phenolic compounds in different organs of P. euphratica, and their relationships with the environmental factors in extremely arid areas were discussed.