The rapid growth of the economy in China has caused dramatic growth in the industrial and agricultural development in the Yellow River (YR) watershed. The hydrology of the YR has changed dramatically due to the climate changes and water management practices, which have resulted in a great variation in the fluxes of riverine nutrients carried by the YR. To study these changes dissolved nutrients in the YR were measured monthly at Lijin station in the downstream region of the YR from 2002 to 2004. This study provides detailed information on the nutrient status for the relevant studies in the lower YR and the Bohai Sea. The YR was enriched in nitrate (average 314 μmol·L⁻¹) with a lower concentration of dissolved silicate (average 131 μmol·L⁻¹) and relatively low dissolved phosphate (average 0.35 μmol·L⁻¹). Nutrient concentrations exhibited substantial seasonal and yearly variations. The annual fluxes of dissolved inorganic nitrogen, phosphate, and silicate in 2004 were 5.3, 2.5, and 4.2 times those in 2002, respectively, primarily due to the increase in river discharge. The relative contributions of nutrient inputs to nitrogen in the YR were: wastewater > fertilizer > atmospheric deposition > soil; while to phosphorus were: wastewater > fertilizer > soil > atmospheric deposition. The ratios of N, P and Si suggest that the YR at Lijin is strongly P-limited with respect to potential phytoplankton growth.

Diatoms comprise up to 40% of annual productivity in the modern ocean, and some stress factors may alter their physiology and survival. Here, we describe the morphological, biochemical and molecular responses that occur during metacaspase-mediated programmed cell death (PCD) in response to silicate limitation in the ubiquitous diatom Skeletonema marinoi. Transmission electron microscopy revealed that vacuolization occurred while the plasma membranes remained intact. Caspase 3-like activity, antioxidant gene expression, phosphatidylserine externalization and activated caspase-like expression were measured using in vivo staining. The results show that each was significantly increased under silicate limitation conditions. Using quantitative reverse transcription-PCR, we identified six distinct putative metacaspase proteins in S. marinoi, and we show that each contains a conserved caspase-like domain and is differentially expressed and that some of their expression profiles were correlated with PCD. Silicate limitation could trigger PCD in S. marinoi as well as an increase of antioxidant genes. PCD could be employed as a strategy to decrease silicate demand of the whole population and probably regulate the fate of S. marinoi.

Few studies have been published on the mechanisms of hypoxia response and tolerance in jellyfish, especially with respect to the regulatory mechanism at the molecular level. In this study, Aurelia sp.1, which is frequently found in Chinese coastal waters, was cultivated in a hypoxic system to determine the molecular mechanisms underlying its hypoxic response by studying the physiological activity, gene expression and metabolite contents in the prolyl hydroxylase domain (PHD)-hypoxia inducible factor (HIF) oxygen-sensing system. Physiological activity; the expression of PHD, HIF, ALDO (fructose-bisphosphate aldolase), PDK (pyruvate dehydrogenase kinase), and LDH (lactate dehydrogenase) genes; and the lactic acid content in medusae were significantly affected by hypoxia. The up-regulation of ALDO, PDK and LDH, which was directly or indirectly induced by HIF, mediated the transition from aerobic respiration to anaerobic glycolysis in the medusae. In polyps, there was a slight increase in the expression of HIF, PHD and ALDO, no obvious change in that of PDK and a slight decrease in that of LDH throughout the experiment; however, these changes were insufficient to induce the shift. This study provides a scientific basis for elucidating the regulatory mechanism underlying the PHD-HIF oxygen-sensing system in Aurelia sp.1.