Litter decomposition in mangrove ecosystems is a key process regulating carbon and nutrient cycling, yet long-term dynamics across tidal gradients and associated microbial succession remain poorly understood, particularly in arid systems. We investigated standardized tea litter decomposition and the associated prokaryotic and eukaryotic microbial communities in sediments and decaying litter over a three-year period across a tidal gradient in a natural arid mangrove ecosystem in Qatar. Using green and red tea as model substrates, we assessed organic mass loss alongside 16S and 18S rRNA gene-based microbial diversity and community composition.
Tea litter decomposition was significantly influenced by interactions between tea type and incubation time, as well as tidal level and incubation time. Green tea decomposed faster than red tea across all tidal zones. In the upper and middle tidal zones, both tea types reached minimum organic mass after 3–9 months, followed by a subsequent increase, whereas in the near-sea zone the lowest mass occurred after three years. Overall, three-year incubation resulted in significantly lower organic mass compared with shorter incubation periods. Organic mass loss differed significantly between upper and middle tidal zones, while the near-sea zone did not differ from either.
Prokaryotic (16S) OTU richness in teabag samples was significantly lower at the seaward site compared with landward sites, although Shannon and Simpson indices showed no consistent tidal pattern. Beta diversity analyses revealed no significant effect of tidal level on prokaryotic community composition in either sediment or teabag samples. Eukaryotic (18S) OTU richness varied with tidal level in both substrates, but post hoc comparisons indicated no significant pairwise differences among sites, and diversity indices again showed no consistent tidal trends. Community composition of eukaryotes was likewise unaffected by tidal level.
Microbial succession during decomposition showed clear taxonomic shifts. In green tea, Thermotogae decreased while Chloroflexi increased over time; in red tea, Proteobacteria declined and Chloroflexi increased. Firmicutes displayed contrasting trajectories between tea types. For eukaryotes, Chlorophyta declined and Bacillariophyta increased over time in green tea, whereas no clear temporal pattern was observed in red tea. Over time, microbial communities associated with tea litter converged toward those in surrounding sediments.
Our findings emphasize the importance of long-term incubation experiments to capture non-linear decomposition dynamics and microbial succession in mangrove ecosystems.