Liu, B; Liu, X; Huo, S; Chen, Xin; Wu, Lin; Chen, M; Zhou, K; Li, Q; Peng, L; ,
Purpose The rhizosphere plays an important role in promoting the biodegradation and phytoremediation processes of organic pollutants in mangrove sediments; however, the mechanisms behind this interaction remain little understood. We analyzed the properties of root exudates and rhizosphere sediment of Bruguiera gymnorrhiza (L.) to provide basic information about the rhizosphere effects of mangroves.Materials and methods We analyzed the organic components and the low-molecular-weight organic acids in root exudates extracted from hydroponic culture solution, and the rhizosphere and non-rhizosphere sediments using gas chromatography-mass spectrometer and high-performance liquid chromatography. A 16S rDNA gene analysis was performed to investigate the bacterial community and diversity of sediments. The sediment organic carbon structures were analyzed using solid-state C-13 nuclear magnetic resonance. A stable carbon isotopic analysis was conducted to assess the contribution of root exudates and litter (root, stem, and leaf) to sediment organic matter.Results and discussion The organic components in the mangrove root exudates were collected from the hydroponic culture solution sediments and included hydrocarbons, esters, phenols, and aromas in both the rhizosphere and non-rhizosphere sediments. However, the content of each component and the dominant components were different between the rhizosphere and non-rhizosphere sediments. The rhizosphere sediment showed a higher level of organic carbon, nutrient elements, cation exchange capacity, microorganism density, enzyme activities, and bacterial diversity than the non-rhizosphere sediment. Litter is the main organic matter resource of the rhizosphere sediment; however, the rhizosphere sediment also received more labile organic matters from root exudates. In the rhizosphere sediment, the percentage of macroaggregates (> 1 mm) and the stability of the physical structure were higher than those of the non-rhizosphere sediment. In addition, the microorganism density and bacterial diversity of macroaggregates was higher than those of mesoaggregates (0.25-1 mm) and microaggregates (< 0.25 mm).Conclusions As a result of the input of root exudates, the rhizosphere sediment had different chemical, physical, and microbial properties from the non-rhizosphere sediment. The predominant properties of the rhizosphere sediment were high content of organic matters, stable physical structure, and high microbial activity. This comprehensive understanding of the rhizosphere effects of mangroves is crucial for further studying of the promoted biodegradation and phytoremediation of organic pollutants in this special system.