To better understand seasonal variation in phytoplankton community structure in the East China Sea (ECS), 4 research cruises were carried out between August 2009 and June 2011 over the continental shelf. Phytoplankton community structure and ambient seawater physicochemical parameters were examined. The phytoplankton community in the ECS was mainly composed of diatoms and dinoflagellates, with 242 taxa in 70 genera of diatoms and 104 taxa in 26 genera of dinoflagellates. Several species of Chlorophyta, Chrysophyta, and Cyanophyta were also observed. Chain-forming diatoms were the most dominant phytoplankton group throughout the year, except in spring when dinoflagellates dominated in coastal waters. Monsoon-induced turbulence played a significant role in regulating the dominance of dinoflagellates among seasons, with calm water favoring the growth of dinoflagellates and turbulent water inhibiting them. Phytoplankton abundance was always higher in coastal than offshore waters, mainly determined by nutrient availability. A Prorocentrum dentatum bloom and a Chaetoceros debilis bloom were observed in the Yangtze River estuary in spring 2011 and fall 2010, respectively. The blooms differed greatly in community diversity and cell abundance distribution, potentially affecting organic carbon export. In general, 3 different hydrographic water systems (coastal water, shelf mixed water, and Kuroshio water) were identified from a temperature−salinity plot of the ECS, and phytoplankton abundance showed spatially and temporally different distribution patterns in these 3 water systems. The nutrient N:P ratio, but not the Si:N ratio, played a significant role in regulating the phytoplankton community structure and the formation of the spring coastal dinoflagellate bloom in the ECS.

13 C-labelled glucose was applied to arable (Broadbalk NPK) and permanent grassland (Woburn Grassland) soils to investigate the response of the soil microbial biomass (SMB) to carbon (C) applied at trace concentrations. Phospholipid fatty acids (PLFA) were used as biomarkers for G+ve (odd-chained and iso/anteiso FA) and G−ve bacteria (mono-unsaturated and cyclic FA), actinobacteria (10-methyl-branched FA), fungi (octadecadienoic acid) and general membrane lipids [16:0,18:0]. Gas chromatography-combustion-stable isotope ratio mass spectrometry (GC-C-IRMS) was used to determine the incorporation of 13 C into individual PLFA in two experiments: first, after application of a single concentration (15 μg C g −1 ) of 13 C-glucose over a time sequence (0, 8, 24, 48, 120 and 240 hours), and second after application at three concentrations (25, 83, 416 μg C g −1 soil after 120 hours). 13 C incorporation into PLFA over time was similar in both soils. However, in the permanent grassland soil, 13 C incorporation was increased in actinobacteria PLFA at 120 hours when [16:0,18:0] was reduced. At 240 hours, 13 C incorporation increased in [16:0,18:0] concurrently with a reduction in G+ve bacteria PLFA. Increasing glucose concentration caused different responses in the SMB of both soils. In the arable soil, all biomarker PLFA concentrations increased at all rates of application. In contrast, in the permanent grassland soil PLFA concentrations were similar to the control in all SMB groups, except G+ve bacteria after the greatest rate of application. However, the δ 13 C values of the same PLFA indicated that uptake of applied 13 C-glucose was proportional to the applied concentration in all groups of soil bacteria in both soils.

No abstract