scholarly journals Spatial and temporal distribution of phytoplankton in Lake Skadar

2012 ◽  
Vol 64 (2) ◽  
pp. 585-595 ◽  
Author(s):  
Jelena Rakocevic
Keyword(s):  
Spatial Heterogeneity ◽  
Phytoplankton Community ◽  
General Pattern ◽  
Seasonal Succession ◽  
Temporal Distribution ◽  
Late Summer ◽  
Early Summer ◽  
Quantitative Composition ◽  
Autumn And Winter ◽  
Lake Skadar

Phytoplankton seasonal succession and spatial heterogeneity were studied in Lake Skadar from February to December 2004. A total of 167 taxa from 6 algal divisions were observed, with Bacillariophyta being best represented (52.8%). The general pattern of phytoplankton seasonal succession in Lake Skadar was: Bacillariophyta in the spring, Chlorophyta in early summer, Cyanobacteria and Chlorophyta in late summer and Bacillariophyta and Chlorophyta in autumn and winter. Distinct spatial heterogeneity was observed. The central, open part of the lake (pelagic zone) was characterized by dominant euplanktonic species, mostly diatoms, whereas the western and northwestern parts (more isolated and shallower) had higher abundance of greens and blue-greens and a higher percentage of resuspended benthic-epiphytic forms in the phytoplankton community. Comparison with former phytoplankton data showed distinct differences in terms of the qualitative and quantitative composition of the phytoplankton community of Lake Skadar, which indicates lake deterioration.

scholarly journals A biodiversity hotspot for Microgastrinae (Hymenoptera, Braconidae) in North America: annotated species checklist for Ottawa, Canada

ZooKeys ◽  
2016 ◽  
Vol 633 ◽  
pp. 1-93 ◽  
Author(s):  
Jose Fernandez-Triana ◽  
Caroline Boudreault ◽  
Joel Buffam ◽  
Ronald Maclean
Keyword(s):  
North America ◽  
General Pattern ◽  
Late Summer ◽  
The United States ◽  
Early Summer ◽  
Individual Species ◽  
Early Fall ◽  
Two Peaks ◽  
Annotated Checklist ◽  
First Time

Microgastrinae wasps (Hymenoptera, Braconidae) from the city of Ottawa and its surroundings (a 50-km radius circle, ~7,800 km2) were studied based on 1,928 specimens collected between 1894 and 2010, and housed in the Canadian National Collection of Insects. A total of 158 species from 21 genera were identified, which is by far the highest number of species ever recorded for a locality in North America. An annotated checklist of species is provided.Choerasparasitellae(Bouché, 1834) andPholetesornanus(Reinhard, 1880) are recorded for the first time in the Nearctic (previously only known from the Palearctic region),Cotesiadepressa(Viereck, 1912) is recorded for the first time in Canada (previously only known from the United States), andCotesiahemileucae(Riley, 1881) andProtapantelesphlyctaeniae(Muesebeck, 1929) are recorded for the first time in the province of Ontario. In Ottawa the most diverse genera areCotesia,Apanteles,Microplitis,Pholetesor,Microgaster, andDolichogenidea, altogether comprising 77% of the species found in the area. A total of 73 species (46%) were represented by only one or two specimens, suggesting that the inventory for Ottawa is still relatively incomplete. Seasonal distribution showed several peaks of activity, in spring, summer, and early fall. That general pattern varied for individual species, with some showing a single peak of abundance either in the summer or towards the end of the season, others species attaining two peaks, in late spring and late summer, or in early summer and early fall, and yet others attaining up to three different peaks, in spring, summer and fall. At least 72 of the Microgastrinae species from Ottawa have been previously associated with 554 species of Lepidoptera as hosts – but those historical literature records are not always reliable and in many cases are based on data from areas beyond Ottawa. Thus, our knowledge of the associations between the 158 species of microgastrine parasitoids and the caterpillars of the 2,064 species of Lepidoptera recorded from Ottawa is still very incomplete.

scholarly journals Seasonal development of iron limitation in the sub-Antarctic zone

2018 ◽  
Vol 15 (14) ◽  
pp. 4647-4660 ◽  
Author(s):  
Thomas J. Ryan-Keogh ◽  
Sandy J. Thomalla ◽  
Thato N. Mtshali ◽  
Natasha R. van Horsten ◽  
Hazel J. Little
Keyword(s):  
Phytoplankton Community ◽  
Late Summer ◽  
Growing Season ◽  
Early Summer ◽  
Seasonal Development ◽  
Iron Availability ◽  
Iron Supply ◽  
Incubation Experiments ◽  
The Mean ◽  
Iron Addition

Abstract. The seasonal and sub-seasonal dynamics of iron availability within the sub-Antarctic zone (SAZ; ∼40–45∘ S) play an important role in the distribution, biomass and productivity of the phytoplankton community. The variability in iron availability is due to an interplay between winter entrainment, diapycnal diffusion, storm-driven entrainment, atmospheric deposition, iron scavenging and iron recycling processes. Biological observations utilizing grow-out iron addition incubation experiments were performed at different stages of the seasonal cycle within the SAZ to determine whether iron availability at the time of sampling was sufficient to meet biological demands at different times of the growing season. Here we demonstrate that at the beginning of the growing season, there is sufficient iron to meet the demands of the phytoplankton community, but that as the growing season develops the mean iron concentrations in the mixed layer decrease and are insufficient to meet biological demand. Phytoplankton increase their photosynthetic efficiency and net growth rates following iron addition from midsummer to late summer, with no differences determined during early summer, suggestive of seasonal iron depletion and an insufficient resupply of iron to meet biological demand. The result of this is residual macronutrients at the end of the growing season and the prevalence of the high-nutrient low-chlorophyll (HNLC) condition. We conclude that despite the prolonged growing season characteristic of the SAZ, which can extend into late summer/early autumn, results nonetheless suggest that iron supply mechanisms are insufficient to maintain potential maximal growth and productivity throughout the season.

Nitrogen fertilization enhances cold tolerance of red spruce seedlings

1989 ◽  
Vol 19 (8) ◽  
pp. 1037-1043 ◽  
Author(s):  
D. H. DeHayes ◽  
M. A. Ingle ◽  
C. E. Waite
Keyword(s):  
Cold Tolerance ◽  
N Uptake ◽  
Late Summer ◽  
N Deposition ◽  
Early Summer ◽  
Red Spruce ◽  
Atmospheric N Deposition ◽  
N Application ◽  
Cold Tolerant ◽  
Autumn And Winter

Red spruce (Picearubens Sarg.) seedlings were treated with one of four concentrations of NH4NO3 (0, 300, 1500, and 3000 kg N•ha−1•year−1) applied to the soil, with and without triple superphosphate, during early, mid-, or late summer. Laboratory freezing assessments indicated that cold tolerance of treated seedlings generally increased with increasing nitrogen (N) uptake, with the exception of the highest N treatment. Seedlings receiving 1500 kg N•ha−1•year−1 were most cold tolerant on most sample dates. In general, these seedlings were hardier than those receiving 300 kg N•ha−1•year−1, which were hardier than unfertilized control seedlings. Seedlings receiving supplemental N also acclimated to cold more rapidly in autumn and deacclimated more slowly in spring than unfertilized controls. Supplemental phosphorus (P) had no influence on cold tolerance, and there was no evidence of a N × P interaction. Significant differences in cold tolerance associated with time of N application (early, mid-, and late summer) were detected in autumn and winter, but not in spring. In general, seedlings receiving N in mid- or late summer were as hardy or hardier than seedlings fertilized in early summer, regardless of the concentration of fertilizer. Significant interactions between N and timing of treatments occurred primarily because N applied in early summer resulted in only a slight increase in cold tolerance, whereas mid- and late summer N application resulted in a substantial increase in cold tolerance. Combined results suggest that it is highly unlikely that either the amount or timing of atmospheric N deposition is responsible for the winter injury frequently observed in red spruce.

scholarly journals Seasonal development of iron limitation in the sub-Antarctic zone

2018 ◽  
Author(s):  
Thomas J. Ryan-Keogh ◽  
Sandy J. Thomalla ◽  
Thato N. Mtshali ◽  
Natasha R. van Horsten ◽  
Hazel Little
Keyword(s):  
Phytoplankton Community ◽  
Late Summer ◽  
Growing Season ◽  
Early Summer ◽  
Seasonal Development ◽  
Iron Availability ◽  
Iron Supply ◽  
Incubation Experiments ◽  
High Nutrient ◽  
Iron Addition

Abstract. The seasonal and sub-seasonal dynamics of iron availability within the sub-Antarctic zone (SAZ, ~ 40–45° S) play an important role in the distribution, biomass and productivity of the phytoplankton community. The variability in iron availability is due to an interplay between winter entrainment, diapycnal diffusion, storm-driven entrainment, iron scavenging and iron recycling processes. Biological observations utilising grow-out iron addition incubation experiments were performed at different stages of the seasonal cycle within the SAZ to determine the importance of these supply mechanisms. Here we demonstrate that at the beginning of the growing season there is sufficient iron to meet the demands of the phytoplankton community, but as the growing season develops the supply mechanisms fail to meet this demand. Phytoplankton increase their photosynthetic efficiency and net growth rates following iron addition from mid to late summer, with no differences determined during early summer; suggestive of seasonal iron depletion and low iron resupply. The result of which is residual macronutrients at the end of the growing season, and the prevalence of the high-nutrient low-chlorophyll (HNLC) condition. We conclude that despite the prolonged growing season characteristic of the sub-Antarctic zone, which can extend into late summer/early autumn, the results suggest that the iron supply mechanisms are insufficient to maintain potential maximal growth and productivity throughout the season.

Growth and carcass characteristics of crossbred and straightbred Hereford steers. I. Post-weaning growth

1981 ◽  
Vol 32 (1) ◽  
pp. 161 ◽  
Author(s):  
JM Thompson ◽  
R Barlow ◽  
B Johnston ◽  
PJ Nicholls
Keyword(s):  
Growth Rate ◽  
Slow Growth ◽  
Carcass Characteristics ◽  
Late Summer ◽  
Coastal Environment ◽  
Early Summer ◽  
Significant Difference ◽  
The Mean ◽  
The Difference ◽  
Autumn And Winter

Post-weaning growth characteristics were examined in 28 Hereford, 27 Brahman x Hereford, 23 Simmental x Hereford and 26 Friesian x Hereford steers which were grazed on pasture in a central coastal environment at Paterson, N.S.W. Sixty-seven steers from a 1973 calving were allocated to three groups to be slaughtered when the mean liveweights of the Herefords were approximately 270, 370 and 470 kg. Thirty-seven steers from a 1974 calving were allocated to two groups to be slaughtered when the average liveweights of the Herefords were 470 and 570 kg. Average daily liveweight gains of the crossbred steers were greater (average 19%) than the Hereford steers from weaning to the four slaughter weights (P < 0.05). Of the crossbreds, the Brahman cross steers grew faster than the Simmental cross steers (P < O.05), although the difference was not significant at the highest slaughter weight. The growth advantage of the crossbreds was mainly realized in the periods of slow growth (mean growth rate of 320 g/day) during the late summer, autumn and winter months. During these periods the Brahman cross steers grew faster than the Herefords by an average of 89% (P < 0.05) and the Simmental and Friesian cross steers grew 39% faster than the Herefords (P < 0.05). In the periods of fast growth (mean growth rate of 667 g/day), during the spring and early summer months, there was no significant difference between the sire breeds in growth rate (P > 0.05).

scholarly journals Modal shift in North Atlantic seasonality during the last deglaciation

2020 ◽  
Vol 16 (1) ◽  
pp. 265-282
Author(s):  
Geert-Jan A. Brummer ◽  
Brett Metcalfe ◽  
Wouter Feldmeijer ◽  
Maarten A. Prins ◽  
Jasmijn van 't Hoff ◽  
...  
Keyword(s):  
North Atlantic ◽  
Sediment Cores ◽  
Seasonal Succession ◽  
Late Summer ◽  
Polar Front ◽  
Early Summer ◽  
Last Deglaciation ◽  
Modal Shift ◽  
The Holocene ◽  
The Last Deglaciation

Abstract. Changeover from a glacial to an interglacial climate is considered as transitional between two stable modes. Palaeoceanographic reconstructions using the polar foraminifera Neogloboquadrina pachyderma highlight the retreat of the Polar Front during the last deglaciation in terms of both its decreasing abundance and stable oxygen isotope values (δ18O) in sediment cores. While conventional isotope analysis of pooled N. pachyderma and G. bulloides shells shows a warming trend concurrent with the retreating ice, new single-shell measurements reveal that this trend is composed of two isotopically different populations that are morphologically indistinguishable. Using modern time series as analogues for interpreting downcore data, glacial productivity in the mid-North Atlantic appears limited to a single maximum in late summer, followed by the melting of drifting icebergs and winter sea ice. Despite collapsing ice sheets and global warming during the deglaciation, a second “warm” population of N. pachyderma appears in a bimodal seasonal succession, separated by the subpolar G. bulloides. This represents a shift in the timing of the main plankton bloom from late to early summer in a “deglacial” intermediate mode that persisted from the glacial maximum until the start of the Holocene. When seawater temperatures exceeded the threshold values, first the “cold” (glacial) then the “warm” (deglacial) populations of N. pachyderma disappeared, whilst G. bulloides with a greater tolerance to higher temperatures persisted throughout the Holocene to the present day in the midlatitude North Atlantic. Single-specimen δ18O of polar N. pachyderma reveals a steeper rate of ocean warming during the last deglaciation than appears from conventional pooled δ18O average values.

SEASONAL CHANGES IN THE GERMINATION RESPONSES OF FALL PANICUM TO TEMPERATURE AND LIGHT

1983 ◽  
Vol 63 (4) ◽  
pp. 973-979 ◽  
Author(s):  
JERRY M. BASKIN ◽  
CAROL C. BASKIN
Keyword(s):  
Late Summer ◽  
Early Spring ◽  
Early Summer ◽  
Temperature Cycle ◽  
Late Autumn ◽  
Fine Mesh ◽  
Temperature Regimes ◽  
June July ◽  
Panicum Dichotomiflorum ◽  
Autumn And Winter

Seeds of fall panicum (Panicum dichotomiflorum Michx.) were buried in fine-mesh nylon bags in soil and exposed to the annual temperature cycle. Fresh seeds and seeds exhumed after 1–15 mo were tested in light and darkness at five temperature regimes simulating those in the field from early spring through late autumn. Freshly matured seeds were dormant, but they came out of dormancy during late autumn and winter. Thus, by spring (April) seeds germinated to near 100% in light at 20/10, 25/15, 30/15 and 35/20 °C. However, except at 35/20 °C during June, July and August, the majority of the seeds required light for germination. In the field, germination does not begin until April when temperatures come within the range of those required for germination. Seeds retained the ability to germinate to a high percentage at 30/15 and 35/20 °C throughout the summer, but they lost this ability at 20/10 °C in early summer and at 25/15 °C in late summer. Thus, seeds stop germinating in early autumn when diurnal field temperatures decrease below about 20–25 °C maximum and 10–15 °C minimum. In autumn, seeds lost the ability to germinate even at the high temperatures, but they regained it by the following January.Key words: Germination, dormancy, after-ripening, fall panicum, summer annual, buried seeds

The effects of cutting frequency on yield of Hunter River lucerne grown at wide and close spacing in the Mediterranean climate of South Australia

1970 ◽  
Vol 10 (46) ◽  
pp. 582 ◽  
Author(s):  
GJ Leach
Keyword(s):  
South Australia ◽  
Late Summer ◽  
Ground Level ◽  
Early Summer ◽  
Late Spring ◽  
Sowing Time ◽  
Wide Spacing ◽  
Close Spacing ◽  
Number Of Stems ◽  
Autumn And Winter

Hunter River lucerne, sown in April, June, and August, was planted out at 60 cm X 60 cm or 20 cm X 20 cm spacings on a red brown earth soil. Plants were cut 2.5 cm above ground level every six to eight weeks (standard cutting), or twice as often (frequent cutting), for two years : the yield of dry matter and number of stems per plant were measured at each cut. Yields were smallest in late summer and autumn, and largest in late spring and early summer. Treatments generally had little effect on the seasonal growth rhythm. Frequent cutting nearly always decreased yields. The relative decrease was greatest when standard cut plants were growing most rapidly in late spring, and it was also greater with wide spacing than close spacing. Wide-spaced plants yielded more per plant, and less per unit area, than close-spaced plants, except in late summer. Sowing time influenced yield only until the middle of the first summer. Number of stems per plant, and the mean weight of each stem, were both smallest in autumn and winter, and largest in spring and early summer. Frequent cutting slightly, and increasingly, decreased stem numbers relative to the number present with standard cutting during the experiment. The number of stems per plant was largest, and generally increased throughout, at wide spacing, whereas at close spacing maximum stem numbers were attained in the establishment year. Weight per stem showed greater seasonal variation than numbers. Low winter yields and low yields with frequent cutting could both be largely attributed to the small stem weights. Some implications of these results for lucerne management, and breeding for yield improvement, are discussed.

scholarly journals Modal shift in North Atlantic seasonality during the last deglaciation

2019 ◽  
Author(s):  
Geert-Jan A. Brummer ◽  
Brett Metcalfe ◽  
Wouter Feldmeijer ◽  
Maarten A. Prins ◽  
Jasmijn van 't Hoff ◽  
...  
Keyword(s):  
North Atlantic ◽  
Sediment Cores ◽  
Isotope Analysis ◽  
Seasonal Succession ◽  
Late Summer ◽  
Polar Front ◽  
Early Summer ◽  
Last Deglaciation ◽  
Modal Shift ◽  
The Last Deglaciation

Abstract. Change-over from a glacial to an interglacial climate is considered as transitional between two stable modes. Palaeoceanographic reconstructions using the polar foraminifera Neogloboquadrina pachyderma highlight the retreat of the polar front during the last deglaciation in terms of both its decreasing abundance and stable oxygen isotope values (δ18O) in sediment cores. While conventional isotope analysis of pooled N. pachyderma shells show a warming trend concurrent with the retreating ice, new single shell measurements reveal that this trend is composed of two isotopically different populations that are morphologically indistinguishable. Using modern time-series as analogues for interpreting down-core data, glacial productivity in the mid North Atlantic appears limited to a single maximum in late summer, followed by the melting of drifting icebergs and winter sea ice. Despite collapsing ice sheets and global warming during the deglaciation, a second warm population of N. pachyderma appears in a bimodal seasonal succession separated by the subpolar G. bulloides. This represents a shift in the timing of the main plankton bloom from late to early summer in a deglacial intermediate mode that persisted for ca. 10,000 years until the last deglaciation ended. When seawater temperatures exceeded the threshold values, first the cold (glacial) then the warm (deglacial) population of N. pachyderma disappeared, whilst G. bulloides with a greater tolerance to higher temperatures persisted throughout the Holocene to the present day in the mid-latitude North Atlantic. Single specimen δ18O of polar N. pachyderma reveal a steeper rate of ocean warming during the last deglaciation than appears from conventional pooled δ18O average values.

Effects of Dried Distillers’ Grains Cube Supplementation for Steers Grazing Introduced Pastures on Animal Performance and Forage Production

2021 ◽  
Vol 99 (Supplement_2) ◽  
pp. 12-13
Author(s):  
Jordan Adams ◽  
Rodney Farris ◽  
Scott Clawson ◽  
Earl Ward ◽  
Paul Beck
Keyword(s):  
Festuca Arundinacea ◽  
Statistical Power ◽  
Cynodon Dactylon ◽  
Animal Health ◽  
Late Summer ◽  
Early Summer ◽  
Distillers Grains ◽  
Forage Production ◽  
Trenbolone Acetate ◽  
Dried Distillers Grains

Abstract We evaluated the effects of supplementing dried distillers’ grains cubes (DDGS) and re-implantation of steers (n = 149; BW = 238 ± 13.8 kg) grazing tall fescue (Festuca arundinacea)/bermudagrass (Cynodon dactylon) pastures (n = 9 pastures, 7.2 ± 2.90 ha) from 14 April to 17 September 2020 (n = 155 d) in a split-plot design on steer performance and forage production. Main plot supplemental treatments (n = 3 pastures/treatment) included 1) Fertilized Control (FC), no supplementation on fertilized pastures (112 kg N/ha); 2) Fertilized Supplement (FS), supplemental DDGS fed at 2.9 kg 3-d/wk on fertilized pastures; and 3) Supplement (S), supplemented DDGS at 0.75% BW/d on unfertilized pastures prorated for 5-d/wk feeding. Steers were previously implanted during receiving with 40 mg trenbolone acetate and 8 mg estradiol (REV-G; Revalor G, Merck Animal Health). On July 7, steers in each pasture were randomly assigned to one of three re-implant treatments: 1) no re-implant; 2) REV-G; or 3) 200 mg progesterone and 20 mg estradiol (Synovex S, Zoetis Animal Health). Steers in FS and S gained more (P &lt; 0.01) than FC throughout the trial and final BW was greater (P &lt; 0.01) for FS and S compared with FC. Unexpectedly, re-implanting had no effect on ADG (P = 0.57) or BW (P = 0.34), but statistical power may be lacking. Supplemental efficiency was greater in the late summer for FS (P = 0.05) compared to S. Fertilizing pastures in FS and FC did not affect biomass (P = 0.39), however, CP was increased (P = 0.01) and acid and neutral detergent fibers tended to decrease (P = 0.06) relative to S in the early summer (April, May, June, and July), but did not differ in late summer (August and September). Based upon our analysis, DDGS is a suitable supplement and can replace N fertilizer for steers grazing introduced pastures.

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