title: High salinity leads to accumulation of soil organic carbon in mangrove soil.
abstract: Although mangrove forests are one of the most well-known soil organic carbon (SOC) sinks, the mechanism underlying SOC accumulation is relatively unknown. High net primary production (NPP) along with the typical bottom-heavy biomass allocation and low soil respiration (SR) have been considered to be responsible for SOC accumulation. However, an emerging paradigm postulates that SR is severely underestimated because of the leakage of dissolved inorganic carbon (DIC) in groundwater. Here we propose a simple yet unique mechanism for SOC accumulation in mangrove soils. We conducted sequential extraction of water extractable organic matter (WEOM) from mangrove soils using ultrapure water and artificial seawater, respectively. A sharp increase in humic substances (HS) concentration was observed only in the case of ultrapure water, along with a decline in salinity. Extracted WEOM was colloidal, and ≤70% of it re-precipitated by the addition of artificial seawater. These results strongly suggest that HS is selectively flocculated and maintained in the mangrove soils because of high salinity. Because sea salts are a characteristic of any mangrove forest, high salinity may be one of mechanisms underlying SOC accumulation in mangrove soils.
authors.affiliation: Graduate School of Agricultural Science, Kobe University, 1 Rokkodai, Nada, Kobe, Hyogo 657-8501, Japan.
authors.forename: Morimaru
authors.initials: M
authors.lastname: Kida
authors.affiliation: Graduate School of Agricultural Science, Kobe University, 1 Rokkodai, Nada, Kobe, Hyogo 657-8501, Japan.
authors.forename: Mitsutoshi
authors.initials: M
authors.lastname: Tomotsune
authors.affiliation: School of Environmental Science, The University of Shiga Prefecture, 2500 Hassaka, Hikone, Shiga 522-8533, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Iimura
authors.affiliation: Faculty of Agriculture, University of the Ryukyus, 1 Senbaru, Nishihara, Nakagami, Okinawa 903-0213, Japan.
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Kinjo
authors.affiliation: River Basin Research Center, Gifu University, 1 Yanagito, Gifu, Gifu 501-1193, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Ohtsuka
authors.affiliation: Graduate School of Agricultural Science, Kobe University, 1 Rokkodai, Nada, Kobe, Hyogo 657-8501, Japan. Electronic address: fujitake@kobe-u.ac.jp.
authors.forename: Nobuhide
authors.initials: N
authors.lastname: Fujitake
mesh_terms: D018533:Biomass; D002244:Carbon / Q000737:chemistry*; D004553:Electric Conductivity; D006812:Humic Substances / Q000032:analysis*; D045483:Rivers; D054712:Salinity; D012492:Salts / Q000737:chemistry; D012623:Seawater / Q000737:chemistry*; D012987:Soil; D012989:Soil Pollutants / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis; D053833:Wetlands
chemical_list: D006812:Humic Substances; D012492:Salts; D012987:Soil; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D002244:Carbon
keywords: Aggregation; Blue carbon; Ecosystem; Flocculation; Humic substances; Salting out