Spatial and seasonal variations in phosphorus speciation along a river in a lowland catchment (Warnow, Germany).

Losses of phosphorus (P) from arable land lead to P enrichment in surface waters and thus to eutrophication. To gain deeper insights into riverine P processing and transport, the temporal and spatial changes of P compounds along the lowland river Warnow and its tributaries were investigated. Surface water samples were taken monthly between August 2016 and August 2017 and analyzed for the four P fractions: dissolved reactive (DRP), dissolved nonreactive (DNP), particulate reactive (PRP) and particulate nonreactive (PNP) phosphorus. P-composition differed between the courses of the upper Warnow and the impounded middle Warnow due to differences in their hydrological conditions. In the catchment of the upper course, riverine lakes were the sources of PNP and DRP during the summer and autumn. From the catchment of the middle course, mainly PRP and DRP had been introduced into the river. The negative relationship between PRP and the chlorophyll (Chla) concentration (rho = -0.43, p < 0.001) indicated that this P fraction is potentially bioavailable. During the rainy summer of 2017, substantially higher amounts of DRP occurred in the whole Warnow river. The potentially bioavailable P fractions (DRP, PRP, DNP) supported phytoplankton growth in the middle course, and the PNP loads increased with increasing biomass. Total phosphorus (TP) loads increased along the Warnow flow path, due to increasing discharge volume. The annual TP load of 40 t to the estuary was dominated by DRP (32%) and PNP (31%), with smaller contributions by PRP and DNP (19% and 18%, respectively). Our results demonstrate that detailed information on P fractions are helpful to understand P-cycling in rivers and its influence on eutrophication processes. This knowledge should be included in the development of effective management strategies for the improvement of water quality.

Stratification, nitrogen fixation, and cyanobacterial bloom stage regulate the planktonic food web structure.

Changes in the complexity of planktonic food webs may be expected in future aquatic systems due to increases in sea surface temperature and an enhanced stratification of the water column. Under these conditions, the growth of unpalatable, filamentous, N2 -fixing cyanobacterial blooms, and their effect on planktonic food webs will become increasingly important. The planktonic food web structure in aquatic ecosystems at times of filamentous cyanobacterial blooms is currently unresolved, with discordant lines of evidence suggesting that herbivores dominate the mesozooplankton or that mesozooplankton organisms are mainly carnivorous. Here, we use a set of proxies derived from amino acid nitrogen stable isotopes from two mesozooplankton size fractions to identify changes in the nitrogen source and the planktonic food web structure across different microplankton communities. A transition from herbivory to carnivory in mesozooplankton between more eutrophic, near-coastal sites and more oligotrophic, offshore sites was accompanied by an increasing diversity of microplankton communities with aging filamentous cyanobacterial blooms. Our analyses of 124 biotic and abiotic variables using multivariate statistics confirmed salinity as a major driver for the biomass distribution of non-N2 -fixing microplankton species such as dinoflagellates. However, we provide strong evidence that stratification, N2 fixation, and the stage of the cyanobacterial blooms regulated much of the microplankton diversity and the mean trophic position and size of the metabolic nitrogen pool in mesozooplankton. Our empirical, macroscale data set consistently unifies contrasting results of the dominant feeding mode in mesozooplankton during blooms of unpalatable, filamentous, N2 -fixing cyanobacteria by identifying the at times important role of heterotrophic microbial food webs. Thus, carnivory, rather than herbivory, dominates in mesozooplankton during aging and decaying cyanobacterial blooms with hitherto uncharacterized consequences for the biogeochemical functions of mesozooplankton.

Differences in the accumulation of phosphorus between vegetative cells and heterocysts in the cyanobacterium Nodularia spumigena.

The cyanobacterium Nodularia spumigena is a species that frequently forms blooms in the Baltic Sea. Accumulation of the vital nutrient phosphorus (P) apparently plays an important role in the ability of this and other cyanobacteria to grow even when dissolved inorganic phosphorus is depleted. However, until now, this has not been studied in N. spumigena at the cellular level. Therefore, in this study, phosphorus incorporation and distribution in cyanobacterial filaments over time was examined by scanning electron microscopy in combination with energy dispersive X-ray analysis (SEM/EDX) and nanoscale secondary ion mass spectrometry (NanoSIMS). Immediately after phosphate addition to a phosphorus-depleted population, the phosphate concentration decreased in the water while intracellular polyphosphate accumulated. Microscopically, phosphorus in form of polyphosphate granules was stored preferentially in vegetative cells, whereas heterocysts remained low in intracellular phosphorus. This information is an essential step towards understanding the phosphorus dynamics of this species and demonstrates that the division of tasks between vegetative cells and heterocysts is not restricted to nitrogen fixation.

Determinación de IL-l usando un sistema de proliferación de timocitos / Determination of IL-l with a timocite proliferative system

La interleukina-1 (IL-1) es un factor soluble producido por células accesorias que constituye la segunda señal necesaria para la activación de células T, dependientes de macrófagos. La determinación de la IL-1 constituye un importante aspecto al medir y estudiar la inmunorreactividad in vitro y la presencia de este factor en fluidos corporales. En el presente trabajo se describe el método de proliferación de timocitos como sistema de medición de la IL-1 adaptado a nuestras condiciones de laboratorio, siendo demostrado que es posible usar otras especies de ratones además de la C3H/Hed (no respondedores al LPS) si se trabaja en el rango propuesto de concentración de LPS; (100 ug ml-1 hasta 10-3 ug ml-1). Se presentan así mismo resultados de la valoración de otros aspectos que afectan la medición tales como: tipo y concentración de los mitógenos usados (Con A, PHA), edad de los animales, tipo y por ciento de suero añadido al cultivo, número de células y tiempo de los cultivos. Se discute la importancia de los inhibidores y las posibles fluctuaciones del test como sistema biológico

Determinación de IL-l usando un sistema de proliferación de timocitos / Determination of IL-l with a timocite proliferative system

La interleukina-1 (IL-1) es un factor soluble producido por células accesorias que constituye la segunda señal necesaria para la activación de células T, dependientes de macrófagos. La determinación de la IL-1 constituye un importante aspecto al medir y estudiar la inmunorreactividad in vitro y la presencia de este factor en fluidos corporales. En el presente trabajo se describe el método de proliferación de timocitos como sistema de medición de la IL-1 adaptado a nuestras condiciones de laboratorio, siendo demostrado que es posible usar otras especies de ratones además de la C3H/Hed (no respondedores al LPS) si se trabaja en el rango propuesto de concentración de LPS; (100 ug ml-1 hasta 10-3 ug ml-1). Se presentan así mismo resultados de la valoración de otros aspectos que afectan la medición tales como: tipo y concentración de los mitógenos usados (Con A, PHA), edad de los animales, tipo y por ciento de suero añadido al cultivo, número de células y tiempo de los cultivos. Se discute la importancia de los inhibidores y las posibles fluctuaciones del test como sistema biológico