Microbial fertilizer and organic manure combined fertilization changes the rhizosphere bacterial community and carotenoids of Citrus reticulata Blanco ‘Orah’

Abstract

Background Citrus reticulata Blanco ‘Orah’ is one of the most widely grown citrus varieties in southern China. It has been proven that microbial fertilizer and organic manure combined fertilization could improve the yields and appearances of ‘Orah’ fruits. However, details regarding the mechanisms underlying the effects of combined fertilization on the agronomic traits and rhizosphere bacterial community of plants still need to be elucidated. Results This study compared the rhizosphere bacterial community and carotenoids of ‘Orah’ with (WYT group) and without (WYCK group) combined fertilization. The WYT group was sprayed with 50 ml Strongreen and 250 g of Yumeiren five times while WYCK group did not sprayed. Combined fertilization increased fruit weight and the Citrus color index (CCI) significantly (P < 0.05). By 16s rRNA sequencing, 7,126 operational taxonomic units (OTU) were obtained. A higher Shannon index was observed in the WYT group compared to that in the WYCK group. Comparison between the two groups showed that Pseudomonas was enriched in the WTY group, and Cyanobacteria was enriched in the WYCK group. At the family level, Phyllobacteriaceae was significantly abundant in the WTY group, whereas Thermosporothrix and Sphingobium were significantly abundant in the WYCK group. A total of 51 carotenoid components were tested using UPLC-MS/MS. In the pulp tissues, 37 carotenoid components were decreased in the WTY group compared to those in the WYCK group. In fruit skin, 24 significantly different components (7 downregulated and 17 upregulated) were identified in WTY compared to those in WYCK. Correlation analysis revealed that the network between OTUs and carotenoids contained seven carotenoid components and four OTUs. Four OTUs, strain TRA3-20 (a eubacterium), Roseiflexus, OPB35, and Fictibacillus contributed to carotenoid accumulation regulation in fruit skin. Conclusions By exploring the complex interactions between soil microbiota and fruit traits, our research has illuminated potential pathways through which these microbial communities influence the biosynthesis and accumulation of carotenoids. In conclusion, this study provides valuable information regarding soil bacterial communities related to carotenoid accumulation in ‘Orah’.