Table 1. The total lignin content of stem xylem and stipular spines in four varieties of Robinia pseudoacacia trees. Sx: Stem xylem; Ss: Stipular spine.

Sample	Klason lignin (%)	Acid-soluble lignin (%)	Total lignin (%)	Significance (Sx vs Ss)
Statistical analysis was performed using paired t-test to compare lignin content between stem xylem (Sx) and stipular spine (Ss) of the same variety. AGT and LC179 are the varieties with large stipular spines, and LC and LC110 are the varieties with small stipular spines. Total lignin contents are presented as mean values ± SD, and the error bars represent standard deviation derived from three independent measurements. Different lowercase letters (a, b) in the 'Significance (Sx vs Ss)' column indicate highly significant differences at the p ≤ 0.001 level (consistent with the obvious numerical gap between Sx and Ss in each variety).
AGT-Sx	22.43	5.56	27.99 ± 0.35	a
AGT-Ss	43.36	5.21	48.57 ± 0.55	b
LC-Sx	19.31	5.26	24.57 ± 0.26	a
LC-Ss	58.45	5.26	63.71 ± 0.33	b
LC110-Sx	20.78	5.74	26.52 ± 0.51	a
LC110-Ss	48.42	5.39	53.81 ± 0.44	b
LC179-Sx	19.87	5.22	25.09 ± 0.28	a
LC179-Ss	48.81	5.20	54.01 ± 0.41	b