Contrasting root length, nutrient content and carbon sequestration of seagrass growing in offshore carbonate and onshore terrigenous sediments in the South China Sea

Zhijian Jiang; Chunyu Zhao; Shuo Yu; Songlin Liu; Lijun Cui; Yunchao Wu; Yang Fang; Xiaoping Huang

doi:10.1016/j.scitotenv.2019.01.175

Contrasting root length, nutrient content and carbon sequestration of seagrass growing in offshore carbonate and onshore terrigenous sediments in the South China Sea

Sci Total Environ. 2019 Apr 20:662:151-159. doi: 10.1016/j.scitotenv.2019.01.175. Epub 2019 Jan 16.

Authors

Zhijian Jiang¹, Chunyu Zhao², Shuo Yu³, Songlin Liu¹, Lijun Cui², Yunchao Wu¹, Yang Fang², Xiaoping Huang⁴

Affiliations

¹ CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Guangzhou 510301, PR China.
² CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Guangzhou 510301, PR China; University of Chinese Academy of Sciences, Beijing 100049, PR China.
³ CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Guangzhou 510301, PR China; Fouth Institute of Oceanography, State Oceanic Administration, Beihai 53600, China.
⁴ CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Guangzhou 510301, PR China; University of Chinese Academy of Sciences, Beijing 100049, PR China. Electronic address: xphuang@scsio.ac.cn.

PMID: 30690350
DOI: 10.1016/j.scitotenv.2019.01.175

Abstract

Due to distinct human disturbances and sediment type, seagrasses growing in offshore carbonate and onshore terrigenous sediments may show contrasting characteristics. A comparison of seagrass morphology, nutrient content and sediment carbon pools was taken for seagrass beds inhabiting offshore carbonate sediments in Xuande Atoll and onshore terrigenous sediments in Hainan Island, South China Sea. Lower nitrogen (N) content was observed in the aboveground (1.1%-2.8%) and belowground (0.4%-1.5%) tissue of seagrasses in Xuande Atoll than in the same species (aboveground: 2.7%-3.6%; belowground: 1.2%-2.8%) in Hainan Island. Greater depletion of leaf δ¹⁵N of Thalassia hemprichii (T. hemprichii) and Halodule pinifolia (H. pinifolia) in Xuande Atoll indicated nitrogen fixation might be the major source of nitrogen in oligotrophic reef environments. The root lengths of the seagrass species in Xuande Atoll were longer than the same species in Hainan Island. Sediment inorganic carbon (SIC) was considerably higher than sediment organic carbon (SOC) in the carbonate sediment, while the opposite trend was found in the terrigenous sediments. The SOC stock in the carbonate and terrigenous sediments was 2.41 ± 0.78 Mg C ha^-1 and 2.20 ± 0.34 Mg C ha^-1 in the top 5 cm, respectively, while the corresponding SIC was 84.38 ± 21.65 Mg C ha^-1 and 1.27 ± 0.51 Mg C ha^-1, respectively. The average CO_{2 net sequestered} in the carbonate sediment in Xuande Atoll and the terrigenous sediment in Hainan Island were -48.22 ± -12.21 Mg C ha^-1 and 1.44 ± 0.03 Mg C ha^-1, respectively. This suggested seagrass sediment was a source of CO₂ during sediment production in the carbonate sediment but a sink of CO₂ in the terrigenous sediment. Thus, the N concentration in seagrass leaf, root length, sediment carbon composition and pools were contrasted between offshore carbonate sediments and onshore terrigenous sediments.

Keywords: Carbon sequestration; Carbonate sediment; Morphology; Nutrient; Seagrass; Terrigenous sediment.

MeSH terms

Alismatales / chemistry*
Alismatales / growth & development*
Carbon / analysis*
Carbon Sequestration*
China
Geologic Sediments / analysis*
Nutrients / analysis*
Oceans and Seas
Plant Roots / growth & development*

Substances

Carbon