Abstract
Reforestation of native Acacia confusa Merr. on landslide areas in Taiwan is important for agroforestry and soil conservation. To ensure high survival and growth vigor, A. confusa seedlings must develop a strong root system. Inoculating of acacia with symbiotic nitrogen-fixing bacteria (NFB) may ameliorate the problems associated with soil nutrient deficiency on landslide sites. In this study, under plastic house condition, a NFB was isolated from the root nodules of native A. confusa and identified as Bradyrhizobium elkanii, and its effects on growth, root system morphology and pullout resistance of acacia seedlings were investigated. Our results revealed that the growth of inoculated seedlings is significantly more vigor than that of the noninoculated controls. The enhancements in height, tap root length, shoot biomass and root biomass were 40, 100, 140 and 130%, respectively. Also, inoculated seedlings had significantly longer total root length (150%), larger external root surface area (130%), larger root volume (70%), and more root tip number (60%) than the controls. Moreover, the inoculated seedlings developed significantly stronger root functional traits, that is, root density (130%), root length density (60%) and specific root length (60%), than the controls. Consistently, the root pullout resistance of inoculated seedlings was significantly higher than that of the noninoculated ones. These results demonstrate that B. elkanii is an effective nitrogen-fixing bacterium capable of enhancing growth, root development and pullout resistance of A. confusa. Key words: Fabaceae, inoculation, nodules, pullout resistance, root morphology.
Highlights
Acacia confusa (Acacia confusa Merr.), belonging to the family of Fabaceae, subfamily Mimosoideae, is an endemic nitrogen-fixing hardwood tree, widespread throughout the island of Taiwan (Huang and Ohashi, 1977)
Wang et al (2008) indicated that rhizobia isolated from A. mangium in Fujian and Guangdong, China belongs to Mesorhizobium, whereas the strain isolated from A. confusa in Guangdong belonged to Bradyrhizobium
A local rhizobial strain isolated from root nodules of A. confusa was identified as B. elkanii
Summary
Acacia confusa (Acacia confusa Merr.), belonging to the family of Fabaceae, subfamily Mimosoideae, is an endemic nitrogen-fixing hardwood tree, widespread throughout the island of Taiwan (Huang and Ohashi, 1977). Acacia confusa has high potential for agroforestry, lumber production and landslide prevention, and reforestation. Bradyrhizobium spp., Azorhizobium spp., and Mesorhizobium sp.) and form nitrogen-fixing nodules, which can fix nitrogen from air and supply nitrogen nutrient to trees for growth and development (Ferro et al, 2000; Zerhari et al, 2000; Dumroese et al, 2009; Ceccon et al, 2011; Diouf et al, 2015; Pereyra et al, 2015). Several studies have demonstrated that inoculation of seedlings (Oryza sativa, Glycine max and Zea mays) with rhizobial strains results in the change of root morphology, that is, increases in nodules, lateral roots, root hairs, root surface area, and total root length (Huang and Ladha, 1997; Ikeda, 1999; Souleimanov et al, 2002)
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