Analysis on floral nectar characteristics among the selected black locust (Robinia spp.) individuals

Abstract

This study aimed to determine the value of honey source on Robinia by analyzing flower morphology and nectar characteristics in floral nectar of eight selected individuals. The mean nectar volume secreted by genus Robinia was 1.7 ± 1.0 µL. Among the samples, PR (R. margaretta) and HR (R. pseudoacacia) secreted the highest and lowest nectar volumes—3.0 ± 1.1 and 1.1 ± 0.7 µL, respectively. The mean sugar concentration was 44.8 ± 6.1% (range, 40.1–51.4%). The ANOVA results revealed a statistically significant difference in nectar volume and sugar concentration among the eight individuals (p < 0.05). The free sugar content ranged from 0.39 (HR) to 0.78 (KR) mg/μL, and nectar sugar contents ranged from 0.31 (HR) to 1.53 (PR) mg per flower. The sucrose/hexose ratio ranged from 0.5 to 3.6, and sucrose was high in all samples. The results of the Kruskal-Wallis H test revealed significant differences in free sugar content (mg/µL), nectar sugar content per flower and sucrose/hexose ratio (p < 0.05). There were close correlations between nectar characteristics and flower morphology as followed; 1) nectar volume and nectar sugar content per flower (r = 0.976), 2) nectar volume and calyx length (r = 0.952), 3) sugar concentration in nectar and length of inflorescence (r = 0.952). Asparagine was the most abundant (average; 60.2%) amino acid, followed in decreasing order by alanine (6.9%), glutamine (5.2%), and serine (4.7%). The results of Kruskal-Wallis H tests showed that the rate of amino acids of alanine, glutamine, glutamic acid, and arginine significantly differed among the samples (p < 0.05).