The pathway of nitrogen assimilation in Datura stramonium L

A survey of the recent literature concerning the assimilation of nitrogen into plant metabolism has been presented. The pathway of nitrate-N assimilation into amino compounds by the leaves and roots of Datura stramonium at different nitrate feeding levels has been investigated using 15N tracer experimentation, enzyme inhibitor studies and enzymological assays. Leaves were fed via their xylem stream with potassium nitrate at -1 -1 two concentration levels: 200 pg. N. ml and 25 JJ8 N. ml , prior to experimentation. Nitrate-15N xylem stream and infiltration feeding experiments on Datura leaves indicate an apparent major routing of newly reduced 15N to glutamine at the high feeding 1 level (200 f8 N. ml-1) and to glutamate at the low feeding level (25 JJ8 N. ml-1). Of the other major soluble amino compounds, serine, glycine, aspartate and alanine were found to be important in the primary assimilation of newly reduced nitrogen. A pre-treatment of the leaves with 5 mM methionine sulphoximine, prior to nitrate-15N infiltration, completely suppressed nitrogen assimilation into amino compounds with the resultant accumulation of 15N in a large ammonia pool. Methionine sulphoximine also caused marked concentration changes in the free amino compound pools, suggesting that conditions of nitrogen stress had been induced. Glutamate dehydrogenase activity (NAD(P)H-dependent) was not inhibited by the methionine sulphoximine pretreatment. Xylem stream feeding of . 15 . ( 15 -1 glutamine- Nat two concentration levels 200 /18 N. ml an

Carbon amendment stimulates benthic nitrogen cycling during the bioremediation of particulate aquaculture waste

The treatment of organic wastes remains one of the key sustainability challenges facing the growing global aquaculture industry. Bioremediation systems based on coupled bioturbation-microbial processing offer a promising route for waste management. We present, for the first time, a combined biogeochemical-molecular analysis of the short-term performance of one such system that is designed to receive nitrogen-rich particulate aquaculture wastes. Using sea cucumbers (Holothuria scabra) as a model bioturbator we provide evidence that adjusting the waste CgN from 5g1 to 20g1 promoted a shift in nitrogen cycling pathways towards the dissimilatory nitrate reduction to ammonium (DNRA), resulting in net NH4+ efflux from the sediment. The carbon amended treatment exhibited an overall net N2 uptake, whereas the control receiving only aquaculture waste exhibited net N2 production, suggesting that carbon supplementation enhanced nitrogen fixation. The higher NH4+ efflux and N2 uptake was further supported by meta-genome predictions that indicate that organic-carbon addition stimulated DNRA over denitrification. These findings indicate that carbon addition may potentially result in greater retention of nitrogen within the system; however, longer-term trials are necessary to determine whether this nitrogen retention is translated into improved sea cucumber biomass yields. Whether this truly constitutes a remediation process is open for debate as there remains the risk that any increased nitrogen retention may be temporary, with any subsequent release potentially raising the eutrophication risk. Longer and larger-scale trials are required before this approach may be validated with the complexities of the in-system nitrogen cycle being fully understood

Suffocating phytoplankton, suffocating waters - red tides and anoxia

The dynamics of O2 depletion in exceptional dinoflagellate blooms, often referred to as red tides or harmful algal blooms (HABs), was investigated in St Helena Bay in the southern Benguela upwelling system in 2013. The transition to bloom decay and anoxia was examined through determination of O2-based productivity and respiration rates. Changes in O2 concentrations in relation to bloom metabolism were tracked by fast response optical sensors following incubation of red tide waters in large volume light-and-dark polycarbonate carboys. Concurrent measurements of nutrients and nutrient uptake rates served to assess the role of nutrient stressors in community metabolism and bloom mortality. The estimates of community productivity and respiration are among the highest values recorded. Nutrient concentrations were found to be low and were unlikely to meet the demands of the bloom as dictated by the rates of nutrient uptake. Ratios of community respiration to gross production were particularly high ranging from 0.6 – 0.73 and are considered to be a function of the inherently high cellular respiration rates of dinoflagellates. Nighttime community respiration was shown to be capable of removing as much as 17.34 ml O2 l-1 from surface waters. These exceptional rates of O2 utilization are likely in some cases to exceed the rate of O2 replenishment via air-water exchange thereby leading overnight to conditions of anoxia. These conditions of nighttime anoxia and nutrient starvation are likely triggers of cell death and bloom mortality further fueling the microbial foodweb and consumption of O2

In situ measurements and model estimates of NO3 and NH4 uptake by different phytoplankton size fractions in the southern Benguela upwelling system.

Bulk measurements can be made of phytoplankton standing stocks on a quasi-synoptic scale but it is more difficult to measure rates of production and nutrient uptake. We present a method to estimate nitrogen uptake rates in productive coastal environments. We use observed phytoplankton cell size distributions and ambient nitrogen concentrations to calculate uptake rates of nitrate, ammonium and total nitrogen by different size fractions of diverse phytoplankton communities in a coastal upwelling system. The data are disaggregated into size categories, uptake rates are calculated and these uptake rates are reaggregated to obtain bulk estimates. The calculations are applied to 72 natural assemblages for which nitrogen uptake rates and particle size distributions were measured textit in situ . The calculated values of total N uptake integrated across all size classes are similar to those of textit in situ bulk measurements (N slope=0.90), (NH _ 4 slope=0.96) indicating dependence of NH _ 4 and total N uptake on ambient N concentrations and cell size distributions of the phytoplankton assemblages. NO _ 3 uptake was less well explained by cell size and ambient concentrations, but regressions between measured and estimated rates were still significant. The results suggest that net nitrogen dynamics can be quantified at an assemblage scale using size dependencies of Michaelis-Menten uptake parameters. These methods can be applied to particle size distributions that have been routinely measured in eutrophic systems to estimate and subsequently analyse variability in nitrogen uptake

Implementation of geohab core reearch project-harnful algal blooms in upwelling systems

Ocean Sciences Meeting, March 2-7, 2008, Orlando, FloridaThe GEOHAB report on HABs in Upwelling Systems (GEOHAB, 2005) specified that GEOHAB would form a Subcommittee for the Upwelling Core Research Project, to work with scientists to ensure coordination of research using the same measurement protocols, sharing data, and contributing to model development. Four major eastern boundary current upwelling systems are represented—the Benguela, Iberian, California, and Humboldt Current—although other systems can be added. The Subcommittee developed 6 potential research projects as a priority for comparative studies including: 1. Effects of nutrients on HAB population dynamics in upwelling systems, 2. Climate and HABs in upwelling systems, 3. Genetic comparisons of HABs in upwelling systems, 4. Coastal morphology and its influence on HABs in upwelling systems, 5. Seeding strategies within upwelling systems and 6. The role of across-shelf and alongshore currents in the transport of HABs in upwelling systems. This presentation will provide an overview and rationale for the programme, and an update on progress towards a collaborative, comparative analysis of these major themes. GEOHAB 2005. Global Ecology and Oceanography of Harmful Algal Blooms, GEOHAB Core Research Project: HABs in Upwelling Systems. G. Pitcher, T. Moita, V. Trainer, R. Kudela, P. Figueras, T. Probyn (Eds.) IOC an SCOR, Paris and Baltimore. 82 pp.N

Harmful algal blooms in coastal upwelling systems

14 pages, 9 figuresThe California Current, Humboldt Current, Canary Current, Iberian Coastal System, and Benguela Current represent five Large Marine Ecosystems (LMEs) associated with eastern boundary upwelling regimes (Figure 1). LMEs are characterized by distinct bathymetry, hydrography, productivity, and trophically dependent populations. Most of the global ocean pollution, overexploitation, and coastal habitat alteration occurs within LME waters. The highly productive upwelling regimes account for a large fraction of global fisheries production (Figure 2), but similar to all other marine environments, are increasingly susceptible to the proliferation and negative effects of harmful algae (Figure 3). These impacts include human and marine organism illness and death due to direct toxic effects, environmental degradation due to, for example, increased biological oxygen demand, declining fisheries and growth of coastal communities, “nuisance” effects such as discoloration of the water, and more subtle changes to the ecology of these marine systemsR. Kudela was funded by NOAA ECOHAB and the National Science FoundationPeer reviewe