Sediment Carbon Sequestration and Driving Factors in Seagrass Beds from Hainan Island and the Xisha Islands

Abstract

Seagrass beds are considered to be substantial sinks of “blue carbon”. However, differentiation in the carbon sink capacities of seagrass beds in different regions with distinct nutrient conditions remains unclear. In this study, sediment carbon stocks, seagrass biomass, and microbial community structures and potential functions of seagrass beds in eutrophic seawater adjacent to Hainan Island and oligotrophic seawater around the Xisha Islands were compared. Our results showed that sediment mineralizable organic carbon and dry bulk density were substantially higher on Hainan Island than on the Xisha Islands (t-test, p < 0.05), while sediment carbon stocks and the total organic carbon were comparable between the two regions (p > 0.05). Similarly, seagrass biomass was much higher on Hainan Island (p < 0.05). Sediment carbon stocks positively correlated with sediment nitrogen and negatively correlated to sediment pH and grain size (p < 0.05). Bacterial diversities were similar in the two regions, while fungi were more diverse on Hainan Island (p < 0.05). Proteobacteria, Desulfobacterota, Ascomycota and Basidiomycota could account for degrading organic carbon on Hainan Island. Proteobacteria and Bacteroidota may contribute primarily to carbon loss in the seagrass beds of the Xisha Islands. This study strengthens our understanding of the effects of human activities on carbon sequestration in seagrass bed ecosystems.

Taxonomic and functional β-diversity patterns reveal stochastic assembly rules in microbial communities of seagrass beds

“…For instance, alterations in rhizosphere microbial communities play a pivotal role in the successful transplantation of seagrasses ( Christiaen et al., 2013 ). Undoubtedly, the ecosystem services provided by seagrass beds, such as high productivity and a robust carbon sequestration capacity ( Fourqurean et al., 2012 ; Han et al., 2023 ), predominantly rely on seagrasses. Therefore, delving into community assembly mechanisms is crucial for understanding of the intricate relationship between microbial communities and seagrasses.…”

“…Due to their short life cycles, rapid community turnover, and sensitivity to the environment, they are excellent subjects for investigating community assemblage ( Vogel et al., 2021a , Vogel et al., 2021b ). Seagrass bed ecosystems are known for their highly diverse habitats and host abundant microbial communities, providing habitats for various marine organisms and numerous ecosystem services ( Yarnall et al., 2022 ; Han et al., 2023 ). These characteristics make seagrass beds an ideal environment for studying microbial community assembly mechanisms ( Santos et al., 2016 ; Du et al., 2020 ).…”

Effects of Aquaculture and Thalassia testudinum on Sediment Organic Carbon in Xincun Bay, Hainan Island

“…Thus, changes in microbial activity and community structure can affect the stability of blue carbon and increase microbial respiration and activity, which could increase the organic carbon mineralization, thereby accelerating carbon loss [39][40][41]. However, to date, there has been limited research conducted on the impact of microorganisms on the carbon cycle in seagrass beds (but see [42]). Studies on how microorganisms respond to nutrient enrichment and, thus, influence organic carbon transformation processes in seagrass beds still need to be strengthened.…”

Seasonality strongly affects short‐term C‐storage in coastal macrophyte communities

“…Overlooking the strong seasonal variability in belowground plant C, for example, could potentially add uncertainty to scaled‐up sediment C stocks from once‐off sampling. Although short‐term C pools (i.e., biomass‐bound C stocks) are increasingly quantified in the marine environment, studies on short‐term C pools have mainly focused on structural elements of plant tissue (e.g., C bound to above and belowground structural tissue; Han et al 2023; Wasserman et al 2023), whereas non‐structural elements (e.g., non‐structural carbohydrates) are rarely considered due to their very short turnover time (Govers et al 2015; Soissons et al 2018). However, plants have evolved a variety of strategies to store short‐term energy reserves in the form of non‐structural carbohydrates (Govers et al 2015; Soissons et al 2018).…”