Relative Preference Index Research Articles

Evaluation of Cicer Milkvetch and Alfalfa Cultivars for Nutritive Value, Anti-Quality Factors and Animal Preference

Cicer milkvetch (CMV; Astragalus cicer L.) is an alternative non-bloat legume to managing alfalfa. A 2-yr study was conducted to compare three CMV cultivars (Oxley II, Oxley, and Veldt) to AC Grazeland alfalfa (ALF; check forage) for nutritive value and animal preference. Each yr, replicate samples (n = 4) of each forage type were harvested late summer and analyzed for nutrient profile. Oxley II had lower (p < 0.05) fiber content than AC Grazeland, while Oxley and Veldt were similar (p = 0.48) to AC Grazeland for neutral detergent fibre (NDF), acid detergent fibre (ADF) and starch. In contrast, Oxley II had higher (p < 0.05) net energy for gain (NEg) than AC Grazeland, and Oxley and Veldt were similar (p > 0.05) to AC Grazeland for NEg. All three CMV varieties had similar levels of total digestible nutrients (TDN) (63.6 ± 0.6%; p > 0.05), but had higher (p = 0.01) energy content than AC Grazeland alfalfa (54.9 ± 1.4% TDN). Selenium (Se) concentrations were similar (p > 0.05) among CVM cultivars and less than 1 mg/kg DM, and no swainsonine or nitrotoxins were detected in the CMV cultivars. The Oxley II CMV tended (p = 0.06) to have a higher (139) relative feed value (RFV) compared to AC Grazeland (94), while Oxley and Veldt had moderate RFV values (128). Dry matter intake of Oxley II, Veldt, and Oxley CMV was 4, 18, and 28% greater than AC Grazeland, respectively. Based on the relative preference index (ratio of forage DMI to AC Grazeland alfalfa DMI), forage types are ranked as follows: AC Grazeland (1.0) < Veldt (1.2) < Oxley (1.4) < Oxley II (1.7). Study results suggest that CMV cultivars harvested late summer, maintained higher forage quality with greater preference compared to alfalfa.

Combined Effects of Experimental Warming and Eutrophication on Phytoplankton Dynamics and Nitrogen Uptake

Shallow lakes are highly vulnerable to damages caused by human activities and warming trends. To assess whether and how community structures of phytoplankton and nitrogen uptake respond to the combined effects of elevated temperature and eutrophication, we performed a mesocosm experiment in field by combining a 4.5 °C increase in temperature and the addition of phosphorus. Our results demonstrated that the combination of rising temperatures and phosphorus loading stimulated the maximum biomass built up by the phytoplankton community, and changed the phytoplankton community by significantly increasing the number of Chlorophyta and Cyanophyta, and decreasing that of Cryptophyta. We also examined the effects of climate warming and eutrophication on phytoplankton nitrogen uptake and dynamics using 15N tracer techniques. The addition of phosphorus slightly increased the phytoplankton nitrate uptake velocity and relative preference index, but decreased the nitrate uptake turnover time. Warming relatively increased the ammonium uptake velocity and the relative preference index, but decreased the ammonium turnover time. In kinetic studies, NH4+ exhibited a higher maximum uptake rate (Vmax) and a lower half-saturation constant (Ks) than NO3− substrates due to temperature elevation and the addition of phosphorus. Hence, warming and eutrophication increased the capacity of phytoplankton for NH4+ uptake and their affinity at low substrate concentrations. Thus, the combined effects of climate warming and phosphorus nutrient availability may increase the prevalence of Chlorophyta and Cyanophyta, and change the nitrogen cycling of aquatic ecosystems.

Microzooplankton Grazing and Phytoplankton Growth in a Chinese Lake

Microzooplankton plays an important role in controlling the standing crop of phytoplankton and primary production. However, research on microzooplankton grazing has mainly focused on the ocean and only rarely on eutrophic lakes. In this study we investigated plankton community structures, microzooplankton grazing rates (m), and phytoplankton growth rates (mu) in order to explore microzooplankton grazing in 2 eutrophic sub-lakes of West Lake, Hangzhou, China (Waihu and Xilihu). Results showed that Pseudanabaena sp. was dominant in Waihu without submerged macrophytes, and the larger phytoplankton (> 2 mu m) biomass was higher than the picophytoplankton (< 2 mu m) biomass. However, Xilihu with macrophytes growing was mainly composed of diatoms and green algae, and there was no significant difference between larger phytoplankton and picophytoplankton biomass. Furthermore, in West Lake, the values of m (ranging from 1.58 similar to 3.33/d) and mu (ranged from 1.38 similar to 3.05/d) were higher than those in the ocean. The higher m, mu, and relative preference index (RPI) for picophytoplankton in Waihu indicated that microzooplankton had a significant size-selective grazing on picophytoplankton. However, no significant size-selection was found in Xilihu. These different responses of plankton in Waihu and Xilihu might explain why larger phytoplankton occupy a dominant position in eutrophic lakes.

Spatial variation of nitrogen uptake rates in the largest brackish water lagoon of Asia (Chilika, India)

Inland and coastal water bodies around the world are susceptible to eutrophication due to inputs of anthropogenic nutrients, such as nitrogen (N) and phosphorus (P). Studies related to quantification of uptake rates of these nutrients and the factors governing these rates are limited in tropical aquatic systems, leading to inadequate understanding of N and carbon (C) cycling in these environments. Here, we report the rates of dissolved inorganic N (DIN) uptake and N2 fixation along with N isotopic composition of particulate organic matter (δ15NPOM) in Asia's largest brackish water lagoon (Chilika, India). The experiments were carried out at sixteen different locations in the lagoon where NO3− and NH4+ uptake rates varied from 0.004 to 1.42 μmol N L−1h−1 (average ∼ 0.51 ± 0.51 μmol N L−1h−1) and 0.19–1.76 μmol N L−1h−1 (average ∼ 1.11 ± 0.43 μmol N L−1h−1), respectively. In general, NH4+ was preferred substrate in the lagoon as depicted from relative preference index (RPINH4+ >1). Despite higher DIN concentrations, the lagoon showed diazotrophic activity as evidenced by considerable N2 fixation rates at majority of stations. Preliminary calculations of the lagoon-wide N budgeting indicate N2 fixation and atmospheric deposition to be significant sources of new N to the lagoon. δ15NPOM in the lagoon ranged from 1.34 to 8.31‰ (average ∼ 3.99 ± 1.68‰) indicating contributions from marine and terrestrial sources along with N2 fixation to the organic matter pool.

A fuzzy multi-criteria group decision making based on ranking interval type-2 fuzzy variables and an application to transportation mode selection problem

In this paper, we propose a fuzzy multi-criteria group decision-making method based on ranking interval type-2 fuzzy variables. First, we present a ranking method developed by relative preference index which we define using generalized credibility measure to rank interval type-2 fuzzy variables. Then, based on the proposed ranking method, we develop a new method to solve fuzzy multi-criteria group decision-making (FMCGDM) problems where linguistic ratings of the alternatives and the criteria weights are represented by interval type-2 fuzzy variables. The proposed FMCGDM method is applied to a transportation mode selection problem to find most preferable mode among available modes based on some selection criteria. The proposed method is simple in computation and important as it uses interval type-2 fuzzy variables which are more reasonable and sensible to represent linguistic terms rather than by type-1 fuzzy variables. A numerical experiment has been done to illustrate the proposed method.

Seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in the southern South China Sea under the influence of the East Asian monsoon

Abstract. To examine seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in oligotrophic tropical waters under the influence of seasonal reversing monsoon, dilution experiments were conducted during the summer of 2009 (21 May to 9 June) and winter 2010 (9 to 18 November) in the southern South China Sea (SSCS). The results showed that environmental variables, phytoplankton biomass, phytoplankton growth rate (μ), microzooplankton grazing rate (m), and correlationship (coupling) between the μ and m, rather than the microzooplankton grazing impact on phytoplankton (m/μ) significantly varied between the two seasons. Higher relative preference index (RPI) for the larger-sized (&gt; 3 μm) phytoplankton than pico-phytoplankton (&lt; 3 μm), indicating significant size-selective grazing by microzooplankton on the larger-sized phytoplankton, were also observed. The μ and m were significantly correlated with seawater salinity and temperature, and phytoplankton biomass, which indicated that salient seasonal variations in the phytoplankton growth and microzooplankton grazing in the SSCS were closely related to the environmental variables under the influence of the East Asian monsoon. We propose that intermittent arrivals of the northeast winter monsoon could lead to the low μ and m, and the decoupling between the μ and m in the SSCS, through influencing nutrient supply to the surface water, and inducing surface seawater salinity decrease. The low m/μ (&lt; 50 % on average) indicates low remineralization of organic matter mediated by microzooplankton and mismatch between the μ and m, and thus probably accounts for part of the high vertical biogenic particle fluxes in the prevailing periods of the monsoons in the SSCS. The size-selective grazing suggests that microzooplankton grazing partially contributes to the pico-phytoplankton dominance in the oligotrophic tropical waters such as that of the SSCS.

Biofilm growth and nitrogen uptake responses to increases in nitrate and ammonium availability

Nitrate (NO3 −) and ammonium (NH4 +) are the two major dissolved inorganic nitrogen (DIN) species available in streams. Human activities increase stream DIN concentrations and modify the NO3 −:NH4 + ratio. However, few studies have examined biofilm responses to enrichment of both DIN species. We examined biofilm responses to variation in ambient concentrations and enrichments in either NO3 − or NH4 +. We incubated nutrient diffusing substrata (NDS) bioassays with three treatments (DIN-free, +NO3 − and +NH4 +) in five streams. Biomass-specific uptake rates (U spec ) of NO3 − and NH4 + were then measured using in situ additions of 15N-labeled NO3 − and NH4 +. Biomass (estimated from changes in carbon content) and algal accrual rates, as well as U spec -NO3 − of biofilms in DIN-free treatments varied among the streams in which the NDS had been incubated. Higher ambient DIN concentrations were only correlated with enhanced biofilm growth rates. U spec -NO3 − was one order of magnitude greater and more variable than U spec -NH4 +, however similar relative preference index (RPI) suggested that biofilms did not show a clear preference for either DIN species. Biofilm growth and DIN uptake in DIN-amended NDS (i.e., +NO3 − and +NH4 +) were consistently lower than in DIN-free NDS (i.e., control). Lower values in controls with respect to amended NDS were consistently more pronounced for algal accrual rates and U spec -NO3 − and for the +NH4 + than for the +NO3 − treatments. In particular, enrichment with NH4 + reduced biofilm U spec -NO3 − uptake, which has important implications for N cycling in high NH4 + streams.

Inorganic nitrogen uptake kinetics of sugarcane (Saccharum spp.) varieties under in vitro conditions with varying N supply

An in vitro system was established for the characterisation of inorganic nitrogen uptake by sugarcane plantlets of variety NCo376. After multiplication and rooting, plantlets (0.27–0.3 g fresh mass) were placed on N-free medium for 4 days, and then supplied with 2–20 mM N as NO3 −-N only, NH4 +-N only or NO3 −-N + NH4 +-N (as 1:1). With few exceptions, on all the tested N media, the in vitro plants always had a higher Vmax for NH4 +-N (28.69–66.51 μmol g−1 h−1) than for NO3 −-N uptake (10.24–30.19 μmol g−1 h−1) and the Km indicated a higher affinity for NO3 −-N (0.02–7.38 mM) than for NH4 +-N (0.06–9.15 mM). When N was applied as 4 and 20 mM to varieties N12, N19 and N36, the interaction between variety, N form and concentration resulted in differences in the Vmax and Km. The high N-use efficient varieties (N12 and N19), as determined in previous pot and field trials, behaved similarly under all tested conditions and displayed a lower Vmax and Km than the low N-use efficient ones (NCo376 and N36). Based on this finding, it was suggested that the N-use efficient designation (from pot and field trials) may not be ascribed solely to N uptake. Assessment of the relative preference index (RPI) for NO3 −-N and NH4 +-N uptake revealed that, at present, the RPI has no application in sugarcane due to its preferential uptake of NH4 +-N.

Fodder Potential and Acceptability of Selected Tree Leaves by Goats

Fodder potential and acceptability of foliages of six selected trees, Afzelia africana, Daniellia oliveri, Acacia seyal, Entada africana, Pterocarpus erinaceus and Securnega virosa, by 12 Red Sokoto bucks (9.8±0.36 kg BW) was determined using cafeteria method in a completely randomized design. Whereas DM, ash, cellulose, NDF, ADF and condensed tannins (CT) were highest in Entada africana, OM, non-fibrous carbohydrate (NFC) and ADL were lowest in the forage. Crude protein and ether extract (EE), and total carbohydrate and phytate were highest and lowest, respectively, in Afzelia africana. Hemicellulose was lowest in Securunega virosa. Intake of DM (g/d and % BW) and relative preference index (RPI) were significantly (P<0.05) lower for Entada africana compared to other tree fodders. Preference ranking followed this order: Afzelia africana > Securunega virosa > Acacia seyal > Daniellia oliveri > Pterocapus erinaceus > Entada africana. The OM digestibility, digestible organic matter and metabolizable energy (ME) were similar (P>0.05) among tree leaves, while ME intake varied significantly (P<0.05). Relative preference index was negatively correlated to DM (r=-0.23, P=0.656), NDF (r= -0.59, P=0.214), ADF (r=-0.34, P=0.505) and phytate (r=-0.09, P=0.865) but positively related to CP (r=0.41, P=0.425), EE (r=0.69, P=0.131) and OM (r=0.53, P=0.283). The CT had a significant negative relationship (r=-0.96, P<0.002) with RPI. Results show that all browse plants are potentially valuable for dry season feeding and as protein and energy supplements.

Stocking Rate and Fuels Reduction Effects on Beef Cattle Diet Composition and Quality

An experiment was conducted to evaluate the influence of forest fuels reduction on diet quality, botanical composition, relative preference, and foraging efficiency of beef cattle grazing at different stocking rates. A split plot factorial design was used, with whole plots (3 ha) being fuel reduced or no treatment (control), and split plots (1 ha) within whole plots were grazed to three levels of forage utilization; (low) 3 heifers·ha−1, (moderate) 6 heifers·ha−1, (high) 9 heifers·ha−1, with a 48-h grazing duration. Grazing treatments were applied in August of 2005 and 2006. Cattle diet composition and masticate samples were collected during 20-min grazing bouts using six ruminally cannulated cows in each experimental unit. Relative preference indices indicated a strong preference for grass regardless of treatment and stocking rate. Grass consumption was lower in control pastures (P<0.05) and tended (P<0.095) to decrease with increased stocking rates. Shrub use was higher in control pastures displaying a quadratic effect (P<0.05) due to stocking, whereas shrub use increased with stocking rate across all treatments. Cattle grazing control pastures consumed diets higher in crude protein compared to cattle grazing treated pastures (P<0.05). In vitro dry matter digestibility values were lower (P<0.05) in control sites and tended (P=0.10) to decrease with increased stocking rates. In both control and treated pastures, bites per minute and grams consumed per minute declined (P=0.003) with increased stocking, indicating foraging efficiency of cattle decreases with increased stocking rates. Our data indicated cattle grazing late season grand fir habitat types have a strong preference for grasses regardless of treatment or stocking rate. However, as stocking rate increased in both control and treated pastures, grass consumption decreased, shrub consumption increased, and foraging efficiency decreased.

Does Nature and Persistence of Substrate at a Mesohabitat Scale Matter for Chironomidae Assemblages? a Study of Two Perennial Mountain Streams in Patagonia, Argentina

Chironomid substrate—specific associations regarding the nature (organic—inorganic) and stability (stable—unstable) of different habitats were investigated at two low order Patagonian streams, during high and low water periods. Nant y Fall and Glyn rivers were visited twice (October 2007 and March 2008) and seven different habitat types were identified. A total of 60 samples were collected using a Surber sampler (0.09 m -2 and 250 µm) and a set of 23 environmental descriptors including physicochemical parameters and different fractions of particulate organic matter were assessed. 35 Chironomidae taxa were recorded with Orthocladiinae (20), Chironominae (7), and Podonominae (4) being the most well—represented subfamilies. Paratrichocladius sp. 1, Parapsectrocladius sp. 2, Parametriocnemus sp. 1, Pseudochironomus sp., and Rheotanytarsus sp. were the most abundant taxa. According to the relative preference index, at least 14 taxa showed strong affinity for a particular substrate. The structurally complex macrophyte Myriophyllum quitense supported 11 taxa compared with only five taxa found on the less complex Isoetes savatieri. Generally, stable substrates (boulders, cobbles, and rooted plants) supported significantly higher chironomids richness, abundance, and diversity than unstable ones (gravel—sand). Canonical correspondence analysis revealed that detritus (leaves, seeds, and biomass), macrophyte biomass, and secondarily hydraulic variables had high explanatory power on chironomids species composition and structure. This work suggests that more complex substrates showing persistence in the temporal dimension supported a diverse array of chironomids, meaning that the maintenance of natural habitat heterogeneity is essential for the community. Land—use practices having significant effects on ecological stream attributes such as increased turbidity, sediment deposition, and runoff patterns will alter assemblages. Understanding environmental associations of the Chironomidae assemblage at the habitat scale is significant for conservation purposes and for the management of low order streams in Patagonia.

Host instar preference and functional response of Aphidius transcaspicus, a parasitoid of mealy aphids (Hyalopterus species)

Aphidiustranscaspicus Telenga (Hymenoptera: Braconidae: Aphidiinae) has been selected for use as a biological control agent against Hyalopteruspruni Geoffroy (Hemiptera: Aphididae) in prune orchards in California. In this study we focus on the host instar preference and functional response of A. transcaspicus. Host instar preference was determined using laboratory arenas by allowing female parasitoids to attack aphids on field-collected leaves of Prunus domestica L. supporting a natural range of H. pruni instars. A relative preference index indicated that A. transcaspicus was 1.4 times more likely to attack intermediate instars (2–4) than 1st or adult instars. The functional response of A. transcaspicus to H. pruni density was determined on enclosed P. domestica shoots in a prune orchard. The functional response to host density was linear (Type I) at the lowest aphid densities, and the asymptotic number of aphids attacked at higher aphid densities was 64.3 ± 6.7 aphids day−1.

Regenerated primary production dominates in a periodically upwelling shelf ecosystem, northeast New Zealand

We present the first field measured primary production values for an intermittently upwelling shelf ecosystem in the Hauraki Gulf, northeast New Zealand. Phytoplankton uptake rates of 13C and 15N were used to determine the relative importance of new (15NO3− ) versus regenerated nutrients (15NH4+ and 15N-urea) to productivity, and to test the hypothesis that the upwelling system supports high export of organic material, acting as a net sink for CO2. From early spring to early summer (1996–1997), deep NO3−-rich waters upwelled onto the shelf and into the inner gulf, producing a short-lived low-level predominantly NO3−-fuelled bloom (surface chlorophyll-a (chl-a) >1.0mgm−3) in early spring. From late spring onwards, mixed layer NO3− concentrations were depleted to often lower levels than NH4+ and urea (∼0.1mmolm−3), with mid-water chl-a maxima associated with the top of the nitracline fuelled predominantly by regenerated nutrients. By late summer, upwelling had ceased, with intrusions of low-nutrient subtropical oceanic surface water producing oligotrophic conditions. NH4+ and urea uptake nearly always exceeded NO3− uptake throughout the euphotic zone, even within the nitracline, with relative preference index (RPI) estimates giving RPIUrea>RPINH4+>RPINO3−, and low uptake f ratios (generally f<0.3), supporting the physiological preference of phytoplankton for reduced forms of nitrogen. Despite periods of upwelling producing relatively high levels of integrated NO3− (typically 25–150mmolNO3−m−2) across the shelf from early spring to early summer, the highest integrated total production (1266mgCm−2d−1) and specific uptake rates of C/chl-a were obtained in late summer. In the inner gulf and on the mid-shelf, these higher late summer production rates coincided with low integrated chl-a biomass and NO3− inventories. There was no correlation of chl-a with C uptake in either surface waters (r2=0.0115), or in the euphotic zone (r2=0.0232) for the compiled data set, raising potential issues of using chl-a data in this region for modelling primary production. Caveats and problems associated with using the new production paradigm, f ratios and e ratios to calculate carbon export from highly dynamic coastal systems are discussed. Contrary to our hypothesis of NO3−-fuelled production in this upwelling system through the spring-to-summer transition, we found relatively high primary production levels were supported by regenerated nutrients most likely derived from the breakdown of NO3− sourced in the nitracline. The resulting pattern of persistent low nutrient uptake f ratios (f<0.3), punctuated only by a brief episode of new production in early spring (f=0.53, outer shelf), resulted in new production accounting for 10–20% of total inorganic nitrogen production, producing low organic material export. In situ oxidation was the primary fate of carbon on the northeast New Zealand continental shelf, where 80–90% of the carbon fixed by phytoplankton was remineralised in the euphotic zone.

Potential habitatsversusfunctional habitats in a lowland braided river (Córdoba, Argentina)

The benthic community of a braided reach of a lowland river was studied with the aim to identify functional habitats through the assessment of potential habitats. Functional habitats were defined considering physical and biological characteristics. Three reaches of the Chocancharava River (Cordoba, Argentina) were selected and six potential habitats were sampled during high and low water periods. Hydraulic and environmental variables were also registered in each sampling occasion. Taxonomic composition, macroinvertebrate abundance, richness, diversity and evenness were estimated for each identified functional habitat. TWINSPAN analysis was applied separately for two data sets (high water and low water period). This analysis showed that samples of the low water period were mainly grouped in relation to three habitats units: vegetated habitats, unvegetated habitats and habitats related to bars. These three habitats were considered functional habitats. The whole biological and environmental data sets were ordinated by Canonical Correspondence Analysis (CCA) showing a significant relationship between benthic assemblages and environmental variables. This analysis grouped samples in relation to the functional habitats identified by TWINSPAN and indicated that the most influential environmental variables explaining the ordination were: current velocity, depth, substrate size and cover percent of rooted emergent macrophytes. Faunal composition determined by CCA for each functional habitat was in agreement with the results obtained by the Relative Preference Index (RPI). Factorial ANOVAs showed that abundance, taxonomic richness, diversity and evenness were different among the functional habitats and that the community attributes were influenced by the effect of the hydrological period and habitat. As the functional habitat approach provides useful tools in management and river rehabilitation the use of this methodology may allow to develop more appropriate restoration strategies to be applied in altered lowland reaches.

Performance and dietary preferences of white-tailed deer grazing chicory, birdsfoot trefoil or alfalfa in north central Alberta.

Little information exists on the performance of deer on alternative forage species in northern temperate environments during summer and fall, the period of inherent maximum growth in deer. In performance and choice experiments, we compared live weight gain (g/kg(0.75)/day), absolute [kg/ha dry matter (DM)] and relative (% DM) herbage utilization, relative preference index (RPI) as well as plant community visitation of white-tailed deer grazing alfalfa (Medicago sativa), birdsfoot trefoil (Lotus corniculatus) or chicory (Cichorium intybus) in north central Alberta, Canada. Herbage phytomass and quality was also measured on the grazed pastures. Alfalfa had higher dry matter yields and crude protein concentrations than chicory and trefoil. Chicory had lower neutral detergent fiber concentrations than the other forages. Tannin concentrations were greatest in birds foot trefoil (nearly 55 g/kg DM), well above those in the other forages (<5 g/kg DM). Live weight gain was similar among deer feeding within the paddocks seeded to birds foot trefoil and chicory, and more than two times higher (p < 0.05) than deer feeding in paddocks seeded to alfalfa. Deer spent more grazing time (about 40%) on chicory pastures than on alfalfa and birds foot trefoil pastures. RPI values were greatest for birds foot trefoil at 2.11, intermediate for chicory at 1.40, and lowest for alfalfa at <0.60. Absolute herbage utilization remained similar (p > 0.05) among the three forage species. In contrast, relative herbage utilization was greater from birds foot trefoil (52% DM) than chicory (40% DM) or alfalfa (25% DM). These results suggest that the use of alfalfa with other alternative forages may prove beneficial to deer production, rather than using alfalfa pasture alone.

CHARACTERIZATION OF SELECTED SPECIATED ORGANIC COMPOUNDS ASSOCIATED WITH PARTICULATE MATTER IN AMBIENT AIR OF THE OUTSKIRTS OF ROME

The organic fraction of airborne particulate matter includes a wide variety of organic compounds, but the present research focus is on Polycyclic Aromatic Hydrocarbons (PAHs) and their nitrated derivatives (nitro-PAHs) because of the well-known health risk associated with these organics. In order to identify and assess the sources of hydrocarbon inputs into the environment n-alkanes content and the relative carbon preference index were utilized. Special consideration was given to nitro-PAHs. The aim of this work was to demonstrate the presence in atmosphere of nitro-PAHs not usually studied, which may be responsible for part of the high direct-acting mutagenic activity of unknown origin observed for the airborne particulate material. Of the 38 particulate-associated nitro-PAH compounds measured, 21 were described for the first time and 17 were detected in real samples, although those 21 nitro-PAHs were reported as positional isomers of corresponding PAHs, with the position of the NO2 group not determined.

Nitrogen ecophysiology of intertidal seaweeds from New Zealand: N uptake, storage and utilisation in relation to shore position and season

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 264:31-48 (2003) - doi:10.3354/meps264031 Nitrogen ecophysiology of intertidal seaweeds from New Zealand: N uptake, storage and utilisation in relation to shore position and season J. C. Phillips1,2,*, C. L. Hurd1 1Department of Botany, University of Otago, PO Box 56, Dunedin, New Zealand 2Present address: CSIRO Marine Research, Private Bag No. 5, Wembley, Western Australia 6913, Australia *Email: julia.phillips@csiro.au ABSTRACT: The nitrogen ecophysiology of 4 intertidal seaweeds (Stictosiphonia arbuscula, Apophlaea lyallii, Scytothamnus australis, Xiphophora gladiata) from southeastern New Zealand is described in terms of N status, N uptake rates and N utilisation. The species growing in the highest shore position had large internal NO3- and NH4+ pools. For all species, tissue NH4+ pools were greater than tissue NO3- pools. Total tissue N was directly related to shore position with high intertidal species having highest tissue N, while the opposite trend was observed for C:N ratios. The ability to take up inorganic (NO3-, NH4+) and organic (urea) N when one or all N forms were present in the culture medium was measured using time-course uptake experiments at initial concentrations of 5 and 30 µM. Nitrate uptake did not vary over time for any of the species. S. arbuscula and S. australis exhibited a surge phase of NH4+ uptake at both concentrations. Urea uptake at 5 µM was generally low and consistent over time; uptake at 30 µM was highly variable. All species were capable of simultaneous uptake of all N forms. The relative importance of each N form to overall N nutrition indicated that NH4+ was an important N source in winter for all species. Urea was an important N source in summer, contributing 27 to 33% to the total N acquisition for most species. A relative preference index indicated that in winter N sources were utilised in the order NH4+ > NO3- > urea, while in summer the order was NH4+ = NO3- > urea. Estimates of the amount of N that each species could acquire during a tidal cycle indicated that the high intertidal S. arbuscula had the greatest capacity for N acquisition, regardless of season. KEY WORDS: Macroalgae · Intertidal seaweed · Nitrogen uptake · Nitrate · Ammonium · Urea · Season · Zonation · New Zealand Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 264. Online publication date: December 15, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Phytoplankton of the Swan–Canning Estuary: a comparison of nitrogen uptake by different bloom assemblages

AbstractSpring chlorophyte‐, summer dinophyte‐ and autumn cryptophyte‐dominated phytoplankton blooms occurring in the upper reaches of the Swan–Canning Estuary have been studied to compare species composition and diurnal distribution and to determine preferential uptake rates for different nitrogen sources. Species distribution patterns over diurnal cycles showed dinophyte and cryptophyte species exhibiting diurnal vertical migration patterns which changed over a three‐week bloom period. The dinophyte and cryptophyte behaviour appeared to be related to measured changes in ambient nitrogen profiles over the course of the bloom. Chlorophyte species were not shown to be strongly migratory over diurnal periods. Absolute uptake rates (ρ, approximating Pmax) for nitrogen, in the form of 15NO3−, 15NH4+ or 15N‐urea, were compared between seasonal bloom assemblages and ranged between 0·02 and 12 µg N l−1 h−1 (NO3 0·02–7; NH4 0·4–9; urea 0·1–12 µg N l−1 h−1). Specific uptake rates (ν) ranged between 2 and 1770 ng N µg Chla−1 h−1 (NO3 2–290; NH4 19–1770; urea 6–1730 ng N µg Chla−1 h−1). Relative preference indices (RPI) for NO3 (new N) vs. NH4 (recycled N) were calculated to determine whether allochthonous or autochthonous nitrogen sources were implicated in supporting these blooms. Results indicated no physiological preference at any depth for NO3 or NH4 during spring and autumn, and for summer surface assemblages. There was a strong preference for NH4 (RPI ∼ 0·95) at mid and bottom depths during summer. Ambient NH4 uptake rates were compared with changes in ambient NH4 profiles to determine the importance of measuring fluxes against absolute parameter measurements in understanding the nitrogen dynamics supporting phytoplankton growth.From flux measurements it was found that apparent reappearance rates for NH4 ranging between 1% and 1030% of absolute uptake rates occurred during summer, with decreases equivalent to 100% of ambient uptake rate occurring at depth at night. Nutrient profiling alone, in the absence of knowledge of nutrient fluxes, was insufficient in assessing possible nutrient control over phytoplankton growth and biomass maintenance. Within this system there is the potential for phytoplankton growth and bloom maintenance to occur supported solely by recycling of NH4. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Utilization of nitrogen and carbon by phytoplankton in Moreton Bay, Australia

Water samples were collected within river mouths, at river plume sites and at well flushed ocean-influenced sites within Moreton Bay, a shallow subtropical embayment in south-eastern Queensland. Rates of inorganic nitrogen (NH+4 and NO-3) and carbon uptake were determined across temporal and spatial scales by use of 15N and 14C incorporation. Phytoplankton productivity, measured as CO2 uptake, was highest at the river mouths. Rates of NH+4 uptake exceeded rates of NO-3 uptake at all sites at all times. Relative preference indices demonstrated a consistent preference by phytoplankton for NH+4 uptake, and NH+4 uptake rates were higher at ocean-influenced sites than at river-mouth sites. Inorganic nutrient and chlorophyll a concentrations were highest at river mouths; however, the greatest NH+4 uptake occurred at the ocean-influenced sites, reflecting a greater dependence on ‘recycled’ N than on ‘new’ N. Biomass-independent NH+4 uptake increased with increasing water temperature; however, NO-3 uptake increased with decreasing water temperature, reflecting the lower temperature optimum for nitrate reductase. The range of NH+4 and NO-3 uptake rates was greater than ranges reported for other coastal waters, reflecting the strong temporal and spatial gradients within Moreton Bay. This trend of strong gradients in C and N dynamics from oligotrophic to river-influenced waters with seasonal flows is likely to exist in many tropical and subtropical coastal waters of Australia.

Nitrogen assimilation and the f-ratio in the northwestern Indian Ocean during an intermonsoon period

Rates of nitrogen assimilation by phytoplankton were measured at 13 stations along a transect in the northwestern Indian Ocean, from the Gulf of Oman, southwards to approximately 8°N, during November and December 1994. Nitrate (NO 3), ammonium (NH 4) and urea assimilation were measured using simulated in situ 15N incubation techniques. These measurements were supported by simultaneous rate measurements of primary production using 14C incubation techniques and detailed vertical distributions of temperature and chlorophyll concentrations. Euphotic zone integrated nitrogen assimilation rates varied between 1.1 and 23.6 mmol N m -2 day -1, with generally higher rates occurring at the northern and southern ends of the transect. At the majority of stations ammonium was the preferred nitrogen substrate assimilated; the average integrated assimilation rate of ammonium being 3.7 mmol N m -2 day -1 compared to 1.6 and 1.8 mmol N m -2 day -1 for urea and nitrate respectively. This general preference is reflected in the low f-ratios, which were ⩽0.52 for all stations and in the relative preference indices (RPI) values which were consistently >1 for ammonium and <1 for nitrate. A further examination of the data has lead to an apparent partitioning of the northwestern Indian Ocean into 2 regions; a region north of 17°30′N and a region south of this, to about 8°N. This division is based on: (i) the relationship between the f-ratio and ambient nitrate levels; (ii) nitrogen assimilation and primary production and (iii) the biomass distribution. It is suggested that this partitioning should be investigated further with the development of biogeochemical provinces in mind and the estimation of f-ratios on much larger, horizontal scales.