Dynamics of nonstructural carbohydrates in seagrass Thalassia hemprichii and its response to shading
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Dynamics of nonstructural carbohydrates in seagrass Thalassia hemprichii and its response to shading JIANG Zhijian1,2 , HUANG Xiaoping1∗ , ZHANG Jingping1,2 1
Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China 2 Tropical Marine Biological Research Station in Hainan, Chinese Academy of Sciences, Sanya 572200, China Received 24 July 2012; accepted 3 February 2013 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2013
Abstract A field survey was performed to examine nonstructural carbohydrate (NSC) dynamics in seagrass Thalassia hemprichii at the Xincun Bay in southern China. An indoor experiment to investigate the response of NSC in T. hemprichii to shade was conducted. Belowground tissue of T. hemprichii was the dominant site of NSC reserves, and soluble sugar was the primary storage compound. The starch content of belowground tissue was lower in high intertidal areas than in low intertidal areas, indicating that the longer air exposure in high intertidal areas resulted in less NSC synthesis and less accumulation of NSC in T. hemprichii. The lowest level of soluble sugar and its proportion to NSC in belowground tissue were observed near the cage culture area, where the nutrient concentration in water and sediment was the highest; while the highest level of that was observed near the coastal shrimp farm, where salinity was the lowest. Soluble sugar in belowground tissue showed the following trend: summer>spring>winter>autumn. This corresponded to seasonal changes in the intensity of light. Leaf sugar accumulated during the autumn-winter period, providing a carbon and energy source for flower bud formation and seed germination. Short-term shading decreased NSC accumulation. Collectively, these results suggest that nutrient enrichment, freshwater discharge and exposure to air affect NSC dynamics in T. hemprichii. Light intensity, flower bud formation, and seed germination were all found to induce seasonal variations in NSC in T. hemprichii. Key words: Thalassia hemprichii, nonstructural carbohydrates, Xincun Bay, dynamics, shade Citation: Jiang Zhijian, Huang Xiaoping, Zhang Jingping. 2013. Dynamics of nonstructural carbohydrates in seagrass Thalassia hemprichii and its response to shading. Acta Oceanologica Sinica, 32(8): 61–67, doi: 10.1007/s13131-013-0342-0
1 Introduction Seagrass beds are important coastal ecosystems. They provide valuable ecological goods and services (Dennison, 2009). In recent years, about 2%–5% of seagrasses populations are lost each year (Duarte and Gattuso, 2010). This decline has been attributed to a wide variety of human and natural disturbances (Manzanera et al., 1998; Neckles et al., 2005; Burkholder et al., 2007; Waycott et al., 2007; Björk et al., 2008; Marbà and Duarte, 2010). The dynamics of nonstructural carbohydrate (NSC) reserves in particular play an important role in determining seagrass growth and its response to environmental disturbances (Touchett
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