The effects of interspecific competition on Diaptomus leptopus in a montane lake: an experimental field study

1983 ◽  
Vol 61 (10) ◽  
pp. 2273-2287 ◽  
Author(s):  
Roberta Jill Olenick
Keyword(s):  
Field Experiments ◽  
Calanoid Copepod ◽  
Interspecific Interactions ◽  
Low Density ◽  
Zooplankton Species ◽  
Respiration Rates ◽  
Survival And Reproduction ◽  
High Concentrations ◽  
Daphnia Rosea ◽  
Standard Density

Despite high densities in an upstream lake, the calanoid copepod Diaptomus leptopus is extremely scarce in oligotrophic montane Eunice Lake, British Columbia. Field experiments tested the hypothesis that competition from zooplankton resident in Eunice Lake prevents immigrant D. leptopus from colonizing.Experiments in 1979 exposed a standard density of D. leptopus to all Eunice Lake zooplankton species at lake densities (control) and at reduced densities (low density), and to all Eunice Lake species except one of Daphnia rosea (Daphnia removal), Diaptomus kenai (kenai removal), or Diaptomus tyrrelli (tyrrelli removal). Improved D. leptopus performance in noncontrol treatments was evidence for competition in controls. Performance measures included density, survival, and reproduction. Similar and poor performances of D. leptopus in control, Daphnia-removal, and kenai-removal treatments plus high concentrations of D. leptopus nauplii in the tyrrelli-removal treatment suggested that only D. tyrrelli competed with D. leptopus. However, similarity between tyrrelli-removal and low-density treatments in D. leptopus naupliar concentrations confounded competition from D. tyrrelli with diffuse competition from several Eunice Lake species combined. Experiments in 1980, designed to separate these effects, provided no evidence of interspecific interactions. Cool 1980 temperatures presumably reduced competition for algal foods by lowering zooplankton respiration rates.

scholarly journals Context-dependent dynamics lead to the assembly of functionally distinct pitcher-plant microbiomes

2019 ◽  
Author(s):  
Leonora S. Bittleston ◽  
Matti Gralka ◽  
Gabriel E. Leventhal ◽  
Itzhak Mizrahi ◽  
Otto X. Cordero
Keyword(s):  
Resource Use ◽  
Bacterial Communities ◽  
Niche Construction ◽  
Interspecific Interactions ◽  
Sarracenia Purpurea ◽  
Strongly Correlated ◽  
Pitcher Plant ◽  
Respiration Rates ◽  
Active Debate ◽  
And Function

AbstractNiche construction through interspecific interactions can condition future community states on past ones. However, the extent to which such history dependency can steer communities towards functionally different states remains a subject of active debate. Using bacterial communities collected from wild pitchers of the carnivorous pitcher plant, Sarracenia purpurea, we tested the effects of history on composition and function across communities assembled in synthetic pitcher plant microcosms. We found that the diversity of assembled communities was determined by the diversity of the system at early, pre-assembly stages. Species composition was also contingent on early community states, not only because of differences in the species pool, but also because the same species had different dynamics in different community contexts. Importantly, compositional differences were proportional to differences in function, as profiles of resource use were strongly correlated with composition, despite convergence in respiration rates. Early differences in community structure can thus propagate to mature communities, conditioning their functional repertoire.

Weed population responses to weed control practices. II. Residual effects on weed populations, control, andGlycine maxyield

Weed Science ◽  
1999 ◽  
Vol 47 (4) ◽  
pp. 423-426 ◽  
Author(s):  
Douglas D. Buhler
Keyword(s):  
Weed Control ◽  
Field Experiments ◽  
High Density ◽  
Residual Effects ◽  
Low Density ◽  
Mechanical Control ◽  
Population Responses ◽  
Setaria Faberi ◽  
History Of ◽  
Broadleaf Species

Weed populations, weed control with imazethapyr, andGlycine maxyields were affected by a 4-yr history of different weed control practices. A range of chemical and mechanical practices were applied in separate field experiments initiated under high and low weed densities. In the high-density experiment, plots kept weed free for 4 yr averaged 24Setaria faberiplants m−2compared with 200 to 600 plants m−2with the various weed control treatments. In plots with a history of mechanical control, weeds not controlled by imazethapyr reducedG. maxyield by 340 kg ha−1compared with plots that were kept weed free during the same period. In the low-density experiment, weed control history had less effect on weed densities. For example,S. faberidensities ranged from 19 plants m−2for the weed-free plots to 195 plants m−2with mechanical control. Weed control history had little effect on weed control with imazethapyr orG. maxyields in imazethapyr-treated plots. While weed-free conditions for 4 yr greatly reduced weed densities, imazethapyr application still increasedG. maxyields 22% in the low-density experiment and 51% in the high-density experiment. Differences in densities of individual annual broadleaf species also developed in response to weed control history in both experiments.

scholarly journals Pro-Degradant Activity of Naturally Occurring Compounds on Polyethylene in Accelerate Weathering Conditions

Materials ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 195 ◽  
Author(s):  
Nadka Tzankova Dintcheva ◽  
Delia Gennaro ◽  
Rosalia Teresi ◽  
Marilena Baiamonte
Keyword(s):  
Thin Films ◽  
Thermal Analysis ◽  
Vitamin E ◽  
Light Exposure ◽  
Low Density Polyethylene ◽  
Accelerated Weathering ◽  
Low Density ◽  
Naturally Occurring ◽  
Accelerate Weathering ◽  
High Concentrations

In this work, naturally occurring compounds, such as Vitamin E (VE) and Ferulic Acid (FA), at high concentrations, have been considered as pro-degradant agents for Low Density Polyethylene (PE). However, all obtained results using the naturally occurring molecules as pro-oxidant agents for PE have been compared with the results achieved using a classical pro-oxidant agent, such as calcium stearate (Ca stearate) and with neat PE. The preliminary characterization, through rheological, mechanical and thermal analysis, of the PE-based systems highlights that the used naturally occurring molecules are able to exert a slight plasticizing action on PE and subsequently the PE rigidity and crystallinity slightly decrease, while the ductility increases. To assess the pro-degradant activity of the considered naturally occurring compounds, thin films of neat PE and PE-based systems containing 2 and 3 wt.% Ca stearate, VE and FA have been produced and subjected to accelerated weathering upon UVB light exposure. All obtained results point out that the VE and FA, at these high concentrations, exert a clear pro-oxidant activity in PE and this pro-oxidant activity is very similar to that exerted by Ca stearate. Moreover, the VE and FA at high concentrations can be considered as suitable eco-friendly pro-degradant additives for PE, also in order to control the polyolefin degradation times.

scholarly journals First-Principles Design of Refractory High Entropy Alloy VMoNbTaW

Entropy ◽  
2018 ◽  
Vol 20 (12) ◽  
pp. 965 ◽  
Author(s):  
Shumin Zheng ◽  
Shaoqing Wang
Keyword(s):  
Elastic Properties ◽  
First Principles ◽  
High Entropy Alloy ◽  
Low Density ◽  
High Entropy ◽  
System A ◽  
Small Influence ◽  
High Concentrations ◽  
General Guidance ◽  
Selection Of

The elastic properties of seventy different compositions were calculated to optimize the composition of a V–Mo–Nb–Ta–W system. A new model called maximum entropy approach (MaxEnt) was adopted. The influence of each element was discussed. Molybdenum (Mo) and tungsten (W) are key elements for the maintenance of elastic properties. The V–Mo–Nb–Ta–W system has relatively high values of C44, bulk modulus (B), shear modulus (G), and Young’s modulus (E), with high concentrations of Mo + W. Element W is brittle and has high density. Thus, low-density Mo can substitute part of W. Vanadium (V) has low density and plays an important role in decreasing the brittleness of the V–Mo–Nb–Ta–W system. Niobium (Nb) and tantalum (Ta) have relatively small influence on elastic properties. Furthermore, the calculated results can be used as a general guidance for the selection of a V–Mo–Nb–Ta–W system.

scholarly journals Planting Density Induced Changes in Cotton Biomass Yield, Fiber Quality, and Phosphorus Distribution under Beta Growth Model

Agronomy ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 500 ◽  
Author(s):  
Aziz Khan ◽  
Xiangjun Kong ◽  
Ullah Najeeb ◽  
Jie Zheng ◽  
Daniel Kean Yuen Tan ◽  
...  
Keyword(s):  
Field Experiments ◽  
Biomass Yield ◽  
Accumulation Rate ◽  
Fiber Quality ◽  
Phosphorus Uptake ◽  
Biomass Accumulation ◽  
Planting Density ◽  
Maximum Height ◽  
Low Density ◽  
Moderate Density

High input costs combined with multiple management and material inputs have threatened cotton productivity. We hypothesize that this problem can be addressed by a single fertilization at flowering with late sowing in a moderately populated plant stand. Field experiments were conducted to evaluate the cotton biomass accumulation, phosphorus dynamics, and fiber quality under three planting densities (low, 3 × 104; moderate, 6 × 104; and dense, 9 × 104 ha−1) and two cultivars (Zhongmian-16 and J-4B). High planting density had 6.2 and 12.6% larger stems and fruiting nodes m−2, while low density produced a 37.5 and 59.4% maximum height node ratio. Moderate density produced 26.4–15.5%, 24.7–12.6%, and 10.5–13.6% higher biomass accumulation rate at the peak bloom, boll set, and plant removal stages over low and high density in both years, respectively. J-4B produced a higher reproductive organs biomass yield when compared with Zhongmian-16 in both years. This higher biomass formation was due to both the higher average (0.8 VT kg·ha−1·d−1) and maximum (1.0 VM kg·ha−1·d−1) reproductive organ phosphorus uptake, respectively. Plants with low density had 5.3–18.5%, 9.5–15%, and 7.8–12.8% greater length, strength, and micronaire values over moderate and dense plants, respectively. Conclusively, moderate density with J-4B is a promising option for improved biomass, phosphorus acquisition, and fiber quality under a short season.

Purple Nutsedge Control with Allyl Isothiocyanate under Virtually Impermeable Film Mulch

2014 ◽  
Vol 28 (1) ◽  
pp. 200-205 ◽  
Author(s):  
Sanjeev K. Bangarwa ◽  
Jason K. Norsworthy
Keyword(s):  
Methyl Bromide ◽  
Field Experiments ◽  
Standard Treatment ◽  
Allyl Isothiocyanate ◽  
Low Density Polyethylene ◽  
Vegetable Production ◽  
Low Density ◽  
Purple Nutsedge ◽  
Treated Soil ◽  
Polyethylene Mulch

Nutsedge control is challenging in commercial vegetable production in the absence of methyl bromide, and therefore, an effective alternative is needed. This study investigated allyl isothiocyanate (ITC) as a methyl bromide alternative for purple nutsedge control under polyethylene-mulch. Greenhouse experiments were conducted to compare the retention of allyl ITC in treated soil (3,000 nmol g−1) under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches. Field experiments were conducted to evaluate the effectiveness of allyl ITC (6 rates: 0, 15, 75, 150, 750, 1500 kg ai ha−1) under VIF mulch against purple nutsedge. Additionally, a standard treatment of methyl bromide+chloropicrin (67 : 33%) at 390 kg ai ha−1under LDPE mulch was included for comparison. In the greenhouse experiment, the predicted half-life of allyl ITC under LDPE and VIF mulch was 0.15 and 0.59 d, respectively. In the field experiment, it was predicted that allyl ITC at 1,240 and 1,097 kg ha−1under VIF mulch is required to control purple nutsedge shoot and tubers equivalent to methyl bromide + chloropicrin at 4 wk after treatment (WAT). It is concluded that allyl ITC under VIF mulch would need to be applied at 2.8 to 3.2 times the standard treatment of methyl bromide + chloropicrin under LDPE mulch for commercially acceptable purple nutsedge control.

A buoyancy mechanism found in cranchid squid

1969 ◽  
Vol 174 (1036) ◽  
pp. 271-279 ◽  
Keyword(s):  
Ammonium Chloride ◽  
Sea Water ◽  
Coelomic Fluid ◽  
Low Density ◽  
Additional Species ◽  
High Concentrations ◽  
Neutrally Buoyant ◽  
Very High

Three species of cranchid squid have been studied at sea and found to be nearly neutrally buoyant in sea water. They each possess a very large coelom filled with a fluid whose density is low in comparison with sea water and this gives a lift sufficient to balance the denser tissues of the animal. This coelomic fluid is nearly iso-osmotic with sea water and its relatively low density arises because it is principally a solution of ammonium chloride in water. The fluid is acid and the significance of this is discussed. Two additional species of cranchid squid whose buoyancies were not measured were also shown to have very high concentrations of ammonium chloride in their coeloms and it seems likely that this buoyancy mechanism is used by all the Cranchidae.

Nitrogen concentrations in field-grown spring barley: an examination of the usefulness of expressing concentrations on the basis of tissue water

1985 ◽  
Vol 105 (2) ◽  
pp. 397-406 ◽  
Author(s):  
R. A. Leigh ◽  
A. B. Johnston
Keyword(s):  
Dry Matter ◽  
Field Experiments ◽  
Spring Barley ◽  
Farmyard Manure ◽  
Limiting Factors ◽  
Stem Tissue ◽  
Tissue Water ◽  
Nitrogen Concentrations ◽  
The Difference ◽  
High Concentrations

SUMMARYA study was made of growth and N concentrations of field-grown crops of spring barley (Hordeum vulgare L. cv. Georgie or Triumph). Nitrogen concentrations were calculated on the basis of both dry matter and tissue water because previous research had indicated that K concentrations expressed on the basis of tissue water were better for assessing the K status of crops. The aim was to see whether this was also the case for N.When supplies of P and K were adequate, the addition of N fertilizer stimulated growth in all crops except when sufficient N was already supplied as farmyard manure. Percentage N in dry matter declined as plants grew and was higher in plants given N than in plants grown without N, although the difference diminished with time. Nitrogen concentrations calculated on the basis of tissue water were very similar for both N-sufficient and N-deficient crops despite large differences in growth rates. Nitrogen concentrations in tissue water also declined but only until anthesis, thereafter they increased. This pre-anthesis decline was due to the increase in the amount of stem tissue which had lower N concentrations in tissue water than leaves. Similarly the post-anthesis increase in N concentrations was due to the development of the ears which had high concentrations of N in tissue water.The effects of deficiencies of P or K or water on N concentrations in tissue water of the cultivars Georgie or Julia were studied also in field experiments at Rothamsted. Lack of P and K inhibited growth of crops given 144 kg N/ha. Crops grown without N grew more slowly than those given N but their growth was not further inhibited by lack of P or K. Deficiencies of either P or K increased N concentrations calculated on the basis of tissue water in crops given 144 kg N/ha but not in crops grown without N. The increase in concentration was not due to changes in the proportions of leaves and stems but to real increases in N concentrations in leaves, stems and ears. Drought decreased growth and also resulted in higher N concentrations in tissue water.In the absence of other limiting factors, N concentrations expressed on the basis of tissue water were very similar for both N-sufficient and N-deficient crops. They increased only when growth was limited by factors other than N. The implications of this for the control of N concentrations by crops is discussed.It is concluded that N concentrations expressed on the basis of tissue water are unlikely to be useful for determining the N requirements of barley. Percentage N in dry matter might be more useful for this purpose.

scholarly journals Induced expression of manganese superoxide dismutase by non-toxic concentrations of oxidized low-density lipoprotein (oxLDL) protects against oxLDL-mediated cytotoxicity

2003 ◽  
Vol 374 (2) ◽  
pp. 505-511 ◽  
Author(s):  
Vladimir A. SHATROV ◽  
Bernhard BRÜNE
Keyword(s):  
Superoxide Dismutase ◽  
Nadph Oxidase ◽  
Manganese Superoxide Dismutase ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density ◽  
Oxidized Low Density Lipoprotein ◽  
Manganese Superoxide ◽  
Low Concentrations ◽  
High Concentrations

Oxidized low-density lipoprotein (oxLDL) affects macrophages and plays a critical role in the development of atherosclerosis. In the present paper, we demonstrate that high concentrations of oxLDL provoked apoptosis of human Mono-Mac-6 cells, which was blocked by diphenylene-iodonium (DPI), an inhibitor of flavin-containing enzymes, such as NADPH oxidase, suggesting the involvement of reactive oxygen species (ROS). Importantly, pre-treatment of cells with low concentrations of oxLDL prevented apoptosis in response to high concentrations of oxLDL by up-regulating manganese superoxide dismutase (MnSOD). DPI prevented expression of MnSOD by oxLDL, whereas inhibitors of cytochrome P450 (methoxalen) or xanthine oxidase (allopurinol) did not, thus pointing to a role of NADPH-oxidase-derived ROS in oxLDL-induced MnSOD expression. Transfection of cells with MnSOD antisense, but not scrambled antisense, oligonucleotides significantly attenuated oxLDL-mediated MnSOD expression and hindered cytoprotective effects of non-toxic oxLDL concentrations. Our findings suggest that up-regulation of MnSOD by low concentrations of oxLDL is critical for protection towards oxLDL-mediated cytotoxicity.

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