Fig. 4

In-depth profile of genes related to nitrogen cycling processes in mangrove sediments. a–c The shifts in functional gene abundance in surficial vs. middle sediments (a), middle vs. deep sediments (b), and surficial vs. deep sediments (c). Arrows indicate the directions of reaction. Red arrows indicate that the gene abundance increased from the surficial sediment to middle/deep sediments, and blue arrows indicate a decreasing trend. The genes adjacent to arrows are representative functional genes for each process, and the numbers in the brackets mean the increased or decreased percentages of gene abundance. *p < 0.05; **p < 0.01; ***p < 0.001