134 / 2023-08-16 23:07:01

Blue carbon sink capacity of mangroves determined by leaves and their associated microbiome

Coastal ecosystem,metagenome sequencing,microbial biomass,functional potential,FT-ICR-MS,mangrove restoration,blue carbon,biogeochemistry,carbon cycling,microbiome

Mangroves play a globally-significant role in carbon capture and storage and are known as blue carbon ecosystems. Yet, there are fundamental biogeochemical processes of mangrove blue carbon formation that are inadequately understood, such as the mechanism by which mangrove afforestation regulates the microbial-driven transfer of carbon from leaf to below-ground blue carbon pool. In this study, we addressed this knowledge gap by investigating: (1) the mangrove leaf characteristics using state-of-the-art FT-ICR-MS; (2) the microbial biomass and their transformation patterns of assimilated plant-carbon; and (3) the degradation potentials of plant-derived carbon in soils of an introduced (Sonneratia apetala) and a native mangrove (Kandelia obovata). We found that biogeochemical cycling took entirely different pathways for S. apetala and K. obovata. Blue carbon accumulation and its contribution of plant-carbon for native mangroves were high, with microbes (dominated by K-strategists) allocating the assimilated-carbon to starch and sucrose metabolism. Conversely, microbes with S. apetala adopted an r-strategy and increased protein- and nucleotide-biosynthetic potentials. These divergent biogeochemical pathways were related to leaf characteristics, with S. apetala leaves characterized by lower molecular-weight, C:N ratio, and lignin content than K. obovata. Moreover, anaerobic-lignin-degradation potentials were high in old-aged soils, but the total degradation potentials were age-independent, explaining that S. apetala age had no significant influences on the contribution of plant-carbon to blue carbon. We propose that for introduced mangroves, newly-fallen leaves decomposed, releasing nutrient-rich organic matter (low molecular weight) that favors growth of r-strategists, which rapidly consume carbon to fuel growth, increasing the contribution of microbial-carbon to blue carbon. In contrast, lignin-rich native mangrove leaves shape microbial communities dominated by K-strategists, which grow slowly and store assimilated-carbon in cells, ultimately promoting the contribution of plant-carbon to the remarkable accumulation of blue carbon. Our study provides new insights into the molecular mechanisms of microbial community responses during reforestation in mangrove ecosystems.