Carbon storage in seagrass soils: long-term nutrient history exceeds theeffects of near-term nutrient enrichment

[摘要] The carbon sequestration potential in coastal soils is linked to abovegroundand belowground plant productivity and biomass, which in turn, is directlyand indirectly influenced by nutrient input. We evaluated the influence oflong-term and near-term nutrient input on aboveground and belowground carbonaccumulation in seagrass beds, using a nutrient enrichment (nitrogen andphosphorus) experiment embedded within a naturally occurring, long-termgradient of phosphorus availability within Florida Bay (USA). We measuredorganic carbon stocks in soils and above- and belowground seagrass biomassafter 17 months of experimental nutrient addition. At the nutrient-limitedsites, phosphorus addition increased the carbon stock in aboveground seagrassbiomass by more than 300 %; belowground seagrass carbon stock increasedby 50–100 %. Soil carbon content slightly decreased ( ∼  10 %)in response to phosphorus addition. There was a strong but non-linearrelationship between soil carbon and Thalassia testudinum leafnitrogen : phosphorus (N : P) or belowground seagrass carbon stock. Whenseagrass leaf N : P exceeded an approximate threshold of 75 : 1, or whenbelowground seagrass carbon stock was less than 100 g m⁻², there wasless than 3 % organic carbon in the sediment. Despite the markeddifference in soil carbon between phosphorus-limited and phosphorus-repleteareas of Florida Bay, all areas of the bay had relatively high soil carbonstocks near or above the global median of 1.8 % organic carbon. Therelatively high carbon content in the soils indicates that seagrass beds haveextremely high carbon storage potential, even in nutrient-limited areas withlow biomass or productivity.

[学科分类] 地球化学与岩石