Soil Carbon, Nitrogen, and Phosphorus Stoichiometry and Fractions in Blue Carbon Ecosystems: Implications for Carbon Accumulation in Allochthonous-Dominated Habitats

Abstract

Blue carbon ecosystems (BCEs) including mangroves, saltmarshes, and seagrasses are highly efficient for organic carbon (OC) accumulation due to their unique ability to trap high rates of allochthonous substrates. It has been suggested that the magnitude of OC preservation is constrained by nitrogen (N) and phosphorus (P) limitation in response to climate and anthropogenic changes. However, little is known about the connection of soil OC with N−P and their forms in response to allochthonous inputs in BCEs. By analyzing soil OC, N, and P densities of BCEs from 797 sites globally, we find that, in China, where allochthonous OC provides 50− 75% of total OC, soil C/P and N/P ratios are 4-to 8-fold lower than their global means, and 23%, 29%, and 20% of buried OC, N, and P are oxidation-resistant fractions that linked with minerals. We estimate that the OC stocks in China should double over the next 40 years under high allochthonous inputs and elevated N/P ratio scenarios during BCE restoration. Allochthonousdominated BCEs thus have the capacity to enhance refractory and mineral bound organic matter accumulation. Protection and restoration of such BCEs will provide long-term mitigating benefits against sea level rise and greenhouse gas emissions.

Microbial Necromass, Lignin, and Glycoproteins for Determining and Optimizing Blue Carbon Formation

“…Therefore, the accumulation of microbial necromass and plant lignin components tends to be divergent in grassland and agricultural ecosystems. ,, Nonetheless, both MNC and lignin contents and their contributions to the SOC pool decrease with salinity in coastal wetlands ( p < 0.01) (Figure S5). This may be due to the allochthonous environment of coastal wetlands, and allochthonous materials leave potential impacts on carbon-nutrient cycling by stoichiometry control . During these processes, the nutrient availability greatly influences microbial activities.…”

“…The results are consistent with the idea that bacterial necromass C is less recalcitrant and thus more degradable. 3,51 Therefore, the increased LAP activities contribute to the observed decrease in microbial necromass. The lignin phenol content increased with NAG activities and Fe SRO contents (p < 0.05) (Figure S5).…”

“…This may be due to the allochthonous environment of coastal wetlands, and allochthonous materials leave potential impacts on carbon-nutrient cycling by stoichiometry control. 3 During these processes, the nutrient availability greatly influences microbial activities. High-salinity sampling sites (S. salsa soils and mudflat soil) showed higher AP contents, lower N:P ratio, and microbial N limitation (Tables S2 and S3).…”

“…Coastal wetland ecosystems cover only 0.5% of the sea floor, yet they account for ∼50% of the C burial in the global ocean. , The sources of soil organic matter (SOM) in coastal wetlands are complex and can stem from both autochthonous (produced within the wetlands) and allochthonous (transported from the uplands and marines) sources . Coastal wetlands have specific soil conditions that differ from other terrestrial ecosystems, such as low oxygen, high salinity, fluctuating hydrological, and redox conditions. , With the projected 5% reduction in the areas of river delta by the end of the 21st century, coastal wetlands are expected to undergo seawater intrusion, altered hydrological conditions, increase in salinity levels, and changes in vegetation composition .…”

“…Moreover, the association of organic matter (OM) with reactive Fe minerals, which offers protection against microbial decomposition, ,, also introduces uncertainty to the fate of SOC. Anaerobic conditions favor the growth of certain microbial groups, such as sulfate and Fe-reducing bacteria, which can promote the reduction of Fe minerals. − Since allochthonous particle deposition and mineral protection act as key biogeochemical controls in the accumulation of SOM in coastal wetlands, further investigations are needed to determine whether redox fluctuations can undermine or promote the capacity of Fe minerals to protect SOM.…”