Initiation of efficient C4 pathway in response to low ambient CO2 during the bloom period of a marine dinoflagellate.

Dinoflagellates are important primary producers and major causative agents of harmful algal blooms in the global ocean. Despite the great ecological significance, the photosynthetic carbon acquisition by dinoflagellates is still poorly understood. The pathways of photosynthetic carbon assimilation in a marine dinoflagellate Prorocentrum donghaiense under both in situ and laboratory-simulated bloom conditions were investigated using a combination of metaproteomics, qPCR, stable carbon isotope and targeted metabolomics approaches. A rapid consumption of dissolved CO2 to generate high biomass was observed as the bloom proceeded. The carbon assimilation genes and proteins including intracellular carbonic anhydrase 2, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase and RubisCO as well as their enzyme activities were all highly expressed at the low CO2 level, indicating that C4 photosynthetic pathway functioned in the blooming P. donghaiense cells. Furthermore, δ13 C values and content of C4 compound (malate) significantly increased with the decreasing CO2 concentration. The transition from C3 to C4 pathway minimizes the internal CO2 leakage and guarantees efficient carbon fixation at the low CO2 level. This study demonstrates the existence of C4 photosynthetic pathway in a marine dinoflagellate and reveals its important complementary role to assist carbon assimilation for cell proliferation during the bloom period.

[Identification of Nitrate Sources and the Fate of Nitrate in Downstream Areas: A Case Study in the Taizi River Basin].

A total of 14 samples were collected in May 2016(dry season)and August 2016 (wet season) in the downstream area of the Taizi River. △15 N-NO3- and △18 O-NO3- were determined using the azide method, and △18 O-H2O was determined using a CO2-H2O equilibration technique. To identify NO3- sources and transformations in the downstream area of Taizi River Basin, ion chromatography, Nessler's reagent spectrophotometry, the azide method, and CO2-H2O equilibration methods were utilized to determine the concentrations of NO3-, Cl-, NH4+-N, and isotopic compositions (△15 N and △18 O) of NO3- and the △18 O-H2O in surface water. The results showed that the NO3- was mainly derived from mixed sources. During the dry season, the nitrate in the surface water was derived from soil nitrogen, manure, and sewage in the upper reaches, and mainly derived from synthetic fertilizer, manure, and sewage in the middle and lower reaches of the Beisha River. The nitrate was mainly derived from manure and sewage in the Nansha River. The nitrate was mainly derived from soil nitrogen in the upper reaches, mainly derived from synthetic fertilizer, manure, and sewage in the middle reaches, and mainly derived from manure and sewage in the lower reaches of the Haicheng River. During the wet season, the nitrate sources in surface water were soil nitrogen, synthetic fertilizer, manure, and sewage in the Beisha River; synthetic fertilizer, manure, and sewage in the middle and lower reaches of the Haicheng River and the Nansha River; and soil nitrogen and synthetic fertilizer in the upper reaches of the Haicheng River. NO3- and NH4+-N concentrations decreased with increasing △15 N-NO3- from the dry season to the wet season, indicating that volatilization of NH4+-N and denitrification of NO3- might occur during the wet season. There is a slightly positive relationship between the reciprocal of the concentration of 1/ρ(NO3-) and △15 N-NO3- during the wet season, indicating that mixing processes occurred in surface water. The results will provide information on nitrate sources during seasonal variations in the plain areas.

Effects of GC temperature and carrier gas flow rate on on-line oxygen isotope measurement as studied by on-column CO injection.

Although deemed important to δ18 O measurement by on-line high-temperature conversion techniques, how the GC conditions affect δ18 O measurement is rarely examined adequately. We therefore directly injected different volumes of CO or CO-N2 mix onto the GC column by a six-port valve and examined the CO yield, CO peak shape, CO-N2 separation, and δ18 O value under different GC temperatures and carrier gas flow rates. The results show the CO peak area decreases when the carrier gas flow rate increases. The GC temperature has no effect on peak area. The peak width increases with the increase of CO injection volume but decreases with the increase of GC temperature and carrier gas flow rate. The peak intensity increases with the increase of GC temperature and CO injection volume but decreases with the increase of carrier gas flow rate. The peak separation time between N2 and CO decreases with an increase of GC temperature and carrier gas flow rate. δ18 O value decreases with the increase of CO injection volume (when half m/z 28 intensity is <3 V) and GC temperature but is insensitive to carrier gas flow rate. On average, the δ18 O value of the injected CO is about 1‰ higher than that of identical reference CO. The δ18 O distribution pattern of the injected CO is probably a combined result of ion source nonlinearity and preferential loss of C16 O or oxygen isotopic exchange between zeolite and CO. For practical application, a lower carrier gas flow rate is therefore recommended as it has the combined advantages of higher CO yield, better N2 -CO separation, lower He consumption, and insignificant effect on δ18 O value, while a higher-than-60 °C GC temperature and a larger-than-100 µl CO volume is also recommended. When no N2 peak is expected, a higher GC temperature is recommended, and vice versa. Copyright © 2015 John Wiley & Sons, Ltd.

[Spatial distribution of methane in surface water and sediment of Jiulongjiang estuary and the effect environment factors of it].

Distribution of methane in surface water and sediment of Jiulongjiang Estuary was investigated during July, 2009 through head-space method. The concentration of methane varies from 10.7 to 456.7 nmol x L(-1) in the surface water at 56 sampled stations, and supersaturates relative to equilibrium with atmospheric methane. The concentration of methane decreases rapidly from estuarine upside margin to the open coastal ocean, resulting from mixing between high CH4-containing fresh water and low CH4-containing seawater. The sediment cores are situated in the upper estuarine coast and seaward boundary along the estuarine salinity gradient, representing the freshwater, half-brackish and marine water environment. Distribution of methane in porewater is consistent with that of surface water, which decreases rapidly from B1, B2, B3 to B4 stations, from 2 212 micromol x L(-1) to 5 micromol x L(-1). The concentration of sulfate in porewater increases gradually from B1, B2, B3 to B4 stations, with average value of 0.13, 0.64, 5.3 and 16.3 mmol x L(-1) respectively. The trends of methane in surface water and porewater have illustrated a large amount of methane is generated via the process of organic matter degradation mediated by methanogens, moved across sediment-water interface, and entered to overlying water. In seaward boundary sediment with an abundance of sulphate in sediment, and sulphate in porewater inhibits the methanogenesis, the methane input from the sediment rapidly decreases. Depth profiles of methane in porewater B2 and B3 stations show an increase in concentration from 43 and 10 micromol x L(-1) near the sediment-water interface to about 1 051 and 57 micromol L(-1) at core end. According to the vertical profile of methane, total organic carbon (TOC) and sulfate trend, a large amount of methane is depleted via anoxic oxidation in methane-sulfate transition. The methane released from the low concentration of sulfate sediment intertidal wetland situated in upper estuarine could be the most important source in Jiulongjiang estuary.